power conversion from milliamps to amps at ultra-high efficiency
TRANSCRIPT
AN54-1
Application Note 54
March 1993
Power Conversion from Milliamps to Amps at Ultra-HighEfficiency (Up to 95%)
and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.Burst Mode is a trademark of Linear Technology Corporation.
Dimitry Goder
Randy Flatness
INTRODUCTION
High efficiency is frequently the main goal for powersupplies in portable computers and hand-held equipment.Efficient converters are necessary in these applications tominimize power drain on the input source (batteries, etc.)and heat buildup in the power components, allowing forsmaller, lighter, and longer-lived systems. Power conver-sion efficiency must be in the 90% range in order to meetthese goals. This application note features power supplycircuits that satisfy these design requirements and attainhigh efficiency over a wide operating range.
The recent development of the LTC®1142, LTC1143,LTC1147, LTC1148, and LTC1149 makes ultra-high effi-ciency conversion possible. In addition, the LTC1148,LTC1149, and LTC1142 are synchronous switching regu-lators, achieving high efficiency conversion at outputcurrents in excess of 10A. These controllers feature a
current mode architecture that has automatic BurstModeTM operation at low currents. This technology makes90% efficiencies possible at output currents as low as10mA, maximizing battery life while a product is in sleepor standby mode.
These ultra-high efficiency converters also implementconstant off-time architecture, fully synchronous switch-ing and low dropout regulation. All these features makethis series of converters a really excellent choice for a vastvariety of applications.
Achieving high efficiency is one of the primary goals ofswitching regulator design. Every application circuit shownin this note includes detailed efficiency graphs. Almost all ofthe magnetic parts used in the circuits are standard prod-ucts, available off-the-shelf from various manufacturers.
Application Note 54
AN54-2
TABLE OF CONTENTSBuckLTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology ................................................................ Figure 1 AN54-3LTC1148: (5V-14V to 5V/2A) Buck Converter .................................................................................................................. Figure 2 AN54-4LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology...................................... Figure 3 AN54-5LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ............................................................. Figure 4 AN54-6LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology ............................................................. Figure 5 AN54-7LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter ..................................................................................... Figure 6 AN54-8LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter .................................................................................... Figure 7 AN54-9LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter ........................................................................................... Figure 8 AN54-10LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs ................ Figure 9 AN54-11LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter ....................................................................................... Figure 10 AN54-12LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter ........................................................................................ Figure 11 AN54-13LTC1149: (16VRMS to 13.8/10A) Buck Converter ........................................................................................................... Figure 12 AN54-14LTC1149: (32VRMS to 27.6V/5A) Buck Converter ........................................................................................................... Figure 13 AN54-15LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology .............................................................. Figure 14 AN54-16LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ........................................................... Figure 15 AN54-17LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology .......................................................... Figure 16 AN54-18LTC1148: (10V-14V to 5V/10A) High Current Buck Convert .......................................................................................... Figure 17 AN54-19LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter ................................................................... Figure 18 AN54-20LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter ................................................................. Figure 19 AN54-21LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter ............................................................... Figure 20 AN54-22LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter ................................................................................ Figure 26 AN54-28LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter ................................................................................ Figure 27 AN54-29LTC1148HV-3.3 (4V-18V to 3.3V/1A) High Voltage Buck Converter .............................................................................. Figure 28 AN54-30LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter ............................................................................... Figure 29 AN54-31LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter ...................................................... Figure 30 AN54-32LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter ............................ Figure 31 AN54-34Single LTC1149: Dual Output Buck Converter ............................................................................................................... Figure 35 AN54-38LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter ................................................................................ Figure 36 AN54-39LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter ......................................................................... Figure 37 AN54-40
Buck-Boost and Inverting TopologiesLTC1148: (4V-14V to 5V/1A) SEPIC Converter .............................................................................................................. Figure 21 AN54-23LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter ................................................................................. Figure 22 AN54-24LTC1148: (4V-10V to – 5V/1A) Positive-to-Negative Converter ...................................................................................... Figure 23 AN54-25LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter .............................................................................................. Figure 24 AN54-26
BoostLTC1148: (2V-5V to 5V/1A) Boost Converter ................................................................................................................. Figure 25 AN54-27
Battery Charging CircuitsLTC1148: High Efficiency Charger Circuit ...................................................................................................................... Figure 32 AN54-35LTC1148: High Voltage Charger Circuit ......................................................................................................................... Figure 33 AN54-36LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger ......................................... Figure 34 AN54-37
Appendix ATopics of Common Interest ........................................................................................................................................................... AN54-40
Appendix BSuggested Manufacturers ............................................................................................................................................................. AN54-42
AN54-3
Application Note 54
LTC1148: (5V-14V to 5V/1A) Buck Converter withSurface Mount Technology
A basic LTC1148 application is shown in Figure 1A. This isa conventional step-down converter that provides 5V out-put at 1A maximum output current. All the componentsused are surface mounted and no heat sink is required.During Q1 on-time, inductor L1's current is sensed by R2and monitored by an internal current sensing comparator.To filter out noise from the current sense waveform, C6 isadded to the circuit. When the current ramp reaches apreset value, Q1 is turned off, and a clamp diode D1 startsconducting for a short period of time, until the internalcontrol logic senses that Q1 is completely off. ThenNDRIVE output goes high turning Q2 on, which shorts outD1. This provides synchronous rectification and signifi-cantly reduces conduction losses during Q1’s off-time.
This regulator has a constant off-time defined by the timingcapacitor C5. To control the output, on-time is varied,
changing the operating frequency and therefore, the dutycycle. If the input voltage is reduced, frequency decreaseskeeping output voltage at the same level. Q1’s on-timestretches to infinity with low input voltage, providing 100%duty cycle and very low dropout. Under dropout condi-tions, the output voltage follows the input, less any resis-tive losses in Q1, L1 and R2.
Under conditions of light output currents, the regulatorenters Burst Mode operation to ensure high efficiency.Continuous operation is interrupted by an internal voltagesensing comparator with built-in hysteresis. in this modeboth Q1 and Q2 are turned off and the comparator monitorsdecreasing output voltage. When the output capacitordischarges below a fixed threshold, operation resumes fora short period of time bringing the output voltage back tonormal. Then the regulator shuts down again conservingquiescent current. Under Burst Mode operation the outputripple is typically 50mV as set by the hysteresis in thecomparator.
Kool Mµ is a registered trademark of Magnetics, Inc.
Figure 1A. LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology
AN54 • F01AC1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V
ITH
CT
SGND PGND
LTC1148-5
VINPDRIVE
SENSE +
SENSE –
NDRIVE
+
C6 0.01µF
+
VIN 5V TO 14V
C1 1µF
R1 1k
C4 3300pF X7R
C5 390pF NPO
10
4
1
8
7
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
C3 22µF × 2 25V
100µH
R2 0.1Ω
5V 1A
C7 220µF 10V
3
11
12
SHUTDOWN
6
C2 0.1µF
+
L1
1
2
4
3
R2 KRL SP-1/2-A1-0R100J Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ® CORE
ALL OTHER CAPACITORS ARE CERAMIC
QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 200mA
Application Note 54
AN54-4
Figure 1B shows efficiency versus output current for threedifferent input voltages. Generally speaking, efficiencydrops as a function of input voltage due to gate chargelosses and LTC1148 DC bias current. The curves convergeat maximum output current as these losses become lesssignificant.
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 1
AN54 • F01B
60
VIN = 6V
VIN = 10V
VIN = 14V
Figure 1B. LTC1148: (5V-14V to 5V/1A) Buck ConverterMeasured Efficiency
Figure 2A. LTC1148: (5V-14V to 5V/2A) Buck Converter
AN54 • F02A
C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL- 1-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE (THROUGH HOLE)
ALL OTHER CAPACITORS ARE CERAMIC
ITH
CT
LTC1148-5
VIN
SENSE +
SENSE –
+
C6 0.01µF
+
VIN 5V TO 14V C1
1µF
R1 1k
C4 3300pF X7R
C5 470pF NPO
10
4
1
8
7
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
C3 22µF × 3 25V
L1 62µH
R2 0.05Ω
5V 2A
C7 220µF × 2 10V
QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 400mA
3
11
12
SHUTDOWN
6
C2 0.1µF
+
SGND PGND
PDRIVE
NDRIVE
LTC1148: (5V-14V to 5V/2A) Buck Converter
A step-down regulator with 2A output current capability isshown in Figure 2A. To provide higher output power levelsthe sense resistor value is decreased, thus increasing thecurrent limit. This also increases maximum allowableripple current in the inductor, so its value can be reduced.Note that timing capacitor C5 is changed to optimizeperformance for a standard inductor value. In this FigureC7 consists of two parallel capacitors ensuring minimumcapacitance requirement for all conditions. A circuit boardhas been laid out for this circuit and has subsequentlybeen thoroughly tested under full operating conditionsand optimized for mass production requirements. A Ger-ber file for the board is available upon request.
AN54-5
Application Note 54
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 2
AN54 • F02B
60
VIN = 6V
VIN = 10V
VIN = 14V
1
Figure 2B. LTC1148: (5V-14V to 5V/2A) Buck ConverterMeasured Efficiency
LTC1148: (5V-14V to 5V/2A) High Frequency BuckConverter with Surface Mount Technology
Figure 3A presents essentially the same circuit as Figure2A, but implementing changes to operate at a higherfrequency. Timing capacitor C5 is reduced to achievehigher switching rate. This approach allows the use of asmaller value inductor with surface mount technology,resulting in a more compact design.
C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX33-4 DCR = 0.06Ω Kool Mµ CORE
ALL OTHER CAPACITORS ARE CERAMIC
ITH
CT
LTC1148-5
VIN
SENSE +
SENSE –
+
C6 0.01µF
+
VIN 5V TO 14V
C1 1µF
R1 1k
C4 3300pF X7R
C5 220pF NPO
10
4
1
8
7
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
C3 22µF × 3 25V
33µH
R2 0.05Ω
5V 2A
C7 220µF × 2 10V
QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 400mA
3
11
12
SHUTDOWN
6
C2 0.1µF
+
L1
1
2
4
3
AN54 • F03A
SGND PGND
PDRIVE
NDRIVE
Figure 3A. LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology
Application Note 54
AN54-6
Figure 4A. LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology
Let us compare efficiency graphs in Figures 2B and 3B.Gate charge losses are directly proportional to operatingfrequency, and as a result the efficiency of Figure 3A is
decreased. However, the effect is most noticeable at highinput voltages and low currents. At maximum load I2Rlosses dominate so that the regulator performance variesonly slightly. These two circuits illustrate the fact that bestoverall efficiency is reached at moderate frequencies. Theyrepresent a nice example of compromising between regu-lator compactness and efficiency.
AN54 • F04A
C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SP-1/2-A1-0R100J Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE ALL OTHER CAPACITORS ARE CERAMIC
ITH
CT
LTC1148-3.3
VIN
SENSE +
SENSE –
+
C6 0.01µF
+
VIN 4V TO 14V C1
1µF
R1 1k
C4 3300pF X7R
C5 560pF NPO
10
4
1
8
7
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
C3 22µF × 2 25V
100µH
R2 0.1Ω
3.3V 1A
C7 220µF 10V
QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 250mA
3
11
12
SHUTDOWN
6
C2 0.1µF
+
L1
1
2
4
3
SGND PGND
PDRIVE
NDRIVE
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 1
AN54 • F03B
60
VIN = 6V
VIN = 10V
VIN = 14V
2
Figure 3B. LTC1148: (5V-14V to 5V/2A) High FrequencyBuck Converter Measured Efficiency
LTC1148: (4V-14V to 3.3V) Buck Converters withSurface Mount Technology
Figures 4A and 5A show application circuits for theLTC1148-3.3 which provides a fixed 3.3V output. Thecircuits deliver 1A and 2A output currents, and use exactlythe same circuit configuration and component values asFigures 1A and 2A. Even though the LTC1148 can achievelow dropout, the minimum input voltage is limited to 4V tomeet requirements for power MOSFET gate drive, and toensure proper operation of the LTC1148 internal circuitry.
AN54-7
Application Note 54
Low output voltage causes efficiency degradation at lightloads when the chip’s DC supply current and gate chargecurrent play major parts in total losses. Figures 4B and
Figure 5A. LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology
5B illustrate this point as the efficiency falls off below10mA output current. High input voltage compounds theproblem.
Figure 4B. LTC1148: (4V-14V to 3.3V/1A) Buck ConverterMeasured Efficiency
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 1
AN54 • F04B
60
VIN = 5V
VIN = 10V
VIN = 14V
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 2
AN54 • F05B
60
1
VIN = 5V
VIN = 10V
VIN = 14V
Figure 5B. LTC1148: (4V-14V to 3.3V/2A) Buck ConverterMeasured Efficiency
AN54 • F05A
C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE (THROUGH HOLE)
ALL OTHER CAPACITORS ARE CERAMIC
ITH
CT
LTC1148-3.3
VIN
SENSE +
SENSE –
+
C6 0.01µF
+
VIN 4V TO 14V C1
1µF
R1 1k
C4 3300pF X7R
C5 470pF NPO
10
4
1
8
7
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
C3 22µF × 3 25V
L1 50µH
R2 0.05Ω
3.3V 2A
C7 220µF × 2 10V
QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 450mA
3
11
12
SHUTDOWN
6
C2 0.1µF
+
SGND PGND
PDRIVE
NDRIVE
Application Note 54
AN54-8
LTC1148: (5V to 3.3V/5A) High EfficiencyStep-Down Converter
Many new microprocessor designs require 3.3V, yet theyare used in systems where 5V is the primary source ofpower. A high efficiency 5V to 3.3V converter is drawn inFigure 6A. It supplies up to 5A load using only surfacemount components. Two P-channel MOSFETs are con-nected in parallel to decrease their conduction losses.Efficiency at 5V input is 90%; this means only 1.6W is lost.The lost power is distributed between RSENSE, L1 and thepower MOSFETs, thus no heat sinking is required. OUTPUT CURRENT (A)
EFFI
CIEN
CY (%
)
100
90
80
700.001 0.1 1 10
AN54 • F06B
0.01
Figure 6B. LTC1148: (5V to 3.3V/5A)Buck Converter Measured Efficiency
Figure 6A. LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter
0V = NORMAL >2V = SHUTDOWN
Q1 Si9433DY
Q2 Si9433DY
+ C1 1µF
C2 0.1µF
C7 0.01µF
L1 5µH
R2 0.02Ω
VOUT 3.3V 5A
+
VIN 5V
C5 150pF NPO
C4 3300pF
R1 470Ω + C6
220µF 10V × 3
C3 33µF 6.3V × 2
D1 MBRS140T3
AN54 • F06A
Q3 Si9410DY
ITH
CT
SGND PGND
LTC1148-3.3
VINPDRIVE
SENSE +
SENSE –
NDRIVE
SHUTDOWN10
4
1
8
7
14
3
11
12
6
C1 TANTALUM C3 PANASONIC ECG-COJB330 C6 AVX (Ta) TPSE227K01R0080 ESR = 0.080Ω IRMS = 1.285A Q1, Q2 SILICONIX PMOS BVDSS = 12V DCRON = 0.075Ω Qg = 60nC Q3 SILICONIX NMOS BVDSS = 30V DCRON = 0.050Ω Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL MP-2A-C1-0R020J Pd = 3W L1 COILTRONICS CTX02-12483-1
AN54-9
Application Note 54
LTC1148: (5V to 3.5V/3A) High EfficiencyStep-Down Converter
Some processors require 3.5V or other intermediate volt-age derived from a 5V supply. A good solution for them isthe circuit in Figure 7A. An adjustable version of theLTC1148 allows precise output voltage adjustment, whilepreserving efficiencies of 95%. The output voltage is setby resistors R3 and R4.
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
65
600.01 0.1
AN54 • F07B
1 4
Figure 7B. LTC1148: (5V to 3.5V/3A)Measured Efficiency
Q1 Si9433DY
AN54• F07A
C6, 0.01µF
C2 0.1µF
VOUT 3.5V 3A
SHUTDOWN100pF
C6 100µF 10V × 3
C3 22µF 25V × 2
R4 10k 1%
L1 10µH
LTC1148
+
C4 3300pF
X7R
1
2
3
4
5
6
7
14
13
12
11
10
9
8
PDRIVE
NC
VIN
CT
INT VCC
ITH
SENSE–
NDRIVE
NC
PGND
SGND
SHUTDOWN
ADJ
SENSE+
C3 AVX (Ta) TPSD226M025R0200 ESR = 0.20Ω IRMS = 0.866A C6 AVX (Ta) TPSD107M01R0100 ESR = 0.10Ω IRMS = 1.225A Q1 SILICONIX PMOS BVDSS = 12V DCRON = 0.110Ω Qg = 20nC Q2 SILICONIX NMOS BVDSS = 30V DCRON = 0.05Ω Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL SL-C1-1/2-0R033J Pd = 1/2W L1 COILTRONICS CTX10-4 DCR = 0.038Ω Kool Mµ CORE
+
R3 18.2k 1%
R2 0.033Ω
D1 MBRS130T3
R1 510Ω
Q2 Si9410DY
VOUT = 1.25V (1 + R3/R4)
+
VIN 5V+
C5 180pF
NPO
Figure 7A. LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter
Application Note 54
AN54-10
LTC1149: (10V-48V to 5V/2A) High VoltageBuck Converter
Previous circuits can accept inputs up to 14V. If higherinput voltage is required the LTC1149 can be used. This ICis designed for inputs of up to 48V. A basic step-downapplication circuit is shown in Figure 8A. It operates in thesame fashion as the circuit in Figure 1A and provides5V/2A output. However, different MOSFETs are used sincethey must withstand 48V between source and drain. Highcurrent efficiency exceeds 92% over wide range of inputvoltages. Since the control and drive circuitry are powereddirectly from the input line, DC bias current and gatecharge current result in slightly lower efficiency at lightand moderate loads due to high input voltage (relative toLTC1148). This characteristic is eliminated in the circuit ofFigure 11A. A circuit board has been laid out for this circuitand has subsequently been thoroughly tested under full
operating conditions and optimized for mass productionrequirements. A Gerber file for the board is available uponrequest.
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 2
AN54 • F08B
60
1
VIN = 12V
VIN = 48V
VIN = 36V
VIN = 24V
Figure 8B. LTC1149: (10V-48V to 5V/2A) High VoltageBuck Converter Measured Efficiency
AN54 • F08A
C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA22OM ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC Q2 IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE
ALL OTHER CAPACITORS ARE CERAMIC
VCC
VCC
CAP
SD1
SD2
ITH
CT
LTC1149-5
PGATE
VIN
SENSE +
SENSE –
NGATE
D1 1N4148
+
C9 0.01µF
+
VIN 10V TO 48V C1
0.1µF
+ C4 1µF
C5 0.1µF
C6 0.068µF
Z5U
R1 1k
C7 3300pF X7R
C8 680pF NPO
3
5
16 10
15
7
6
1 4
9
8
13
C3 0.047µF Z5U
Q1 IRFU9024
Q2 IRFU024
D2 MBR160
C2 330µF 63V
L1 62µH
R2 0.05Ω
5V 2A
C10 220µF × 2 10V
QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA
2
11
12
14
SGND PGND
PDRIVE
RGND
Figure 8A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter
AN54-11
Application Note 54
LTC1149: (10V-48V to 5V/2A) High Voltage BuckConverter with Large P-Channel and N-ChannelMOSFETs
Figure 9A is similar to Figure 8A with much larger MOSFETs(TO220 package). These transistors have lower RDS(ON)which reduces their I2R losses by roughly a factor of 2.However, the efficiency improves (compared to Figure8B) only at 2A output current with minimum input voltage.Under other conditions higher gate capacitance causesincreased gate charge current leading to higher driverloss. Also for high input voltages (roughly greater than24V), transition losses play a significant part. These lossesare proportional to the reverse transfer capacitance CRSS,maximum output current, and the square of input voltage.Larger CRSS for the oversized P-channel MOSFET causesan efficiency drop (especially for higher input voltages).
Remember, the “best” MOSFET selection depends on theparticular application.
Figure 9B. LTC1149: (10V-48V to 5V/2A) Measured Efficiencywith Large P-Channel and N-Channel MOSFETs
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 2
AN54 • F09B
60
1
VIN = 12V
VIN = 48V
VIN = 24V
VIN = 36V
AN54 • F09A
C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC Q2 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE ALL OTHER CAPACITORS ARE CERAMIC
VCC
VCC
CAP
SD1
SD2
ITH
CT
LTC1149-5
VIN
SENSE +
SENSE –
D1 1N4148
+
C9 0.01µF
+
VIN 10V TO 48V
C1 0.1µF
+ C4 1µF
R1 1k
C7 3300pF X7R
C8 680pF NPO
3
5
16 10
15
7
6
1 4
9
8
13
C3 0.047µF Z5U
Q1 IRF9Z34
Q2 IRFZ34
D2 MBR160
C2 330µF 63V
L1 62µH
R2 0.05Ω
5V 2A
C10 220µF × 2 10V
QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 560mA
2
11
12
14
PGATE
NGATESGND PGND
PDRIVE
RGND
C5 0.1µF
C6 0.068µF
Z5U
Figure 9A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs
Application Note 54
AN54-12
LTC1149: (10V-48V to 3.3V/2A) High VoltageBuck Converter
If 3.3V has to be generated efficiently from a high voltageinput, use the circuit of Figure 10A. It copies the configu-ration presented in Figure 8A but uses the LTC1149-3.3regulator to provide a precise 3.3V output. In spite ofthe high input and low output voltages, efficiency stillreaches 92%.
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 2
AN54 • F10B
60
1
VIN = 48V
VIN = 12V
VIN = 36V
VIN = 24V
Figure 10B. LTC1149: (10V-48V to 3.3V/2A) High VoltageBuck Converter Measured Efficiency
Figure 10A. LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter
AN54 • F10A
C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC Q2 IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE
ALL OTHER CAPACITORS ARE CERAMIC
VCC
VCC
CAP
SD1
SD2
ITH
CT
LTC1149-3.3
VIN
SENSE +
SENSE –
D1 1N4148
+
C9 0.01µF
+
VIN 10V TO 48V C1
0.1µF
+ C4 1µF
C5 0.1µF
C6 0.068µF
Z5U
R1 1k
C7 3300pF X7R
C8 470pF NPO
3
5
16 10
15
7
6
1 4
9
8
13
C3 0.047µF Z5U
Q1 IRFU9024
Q2 IRFU024
D2 MBR160
C2 330µF 63V
L1 50µH
R2 0.05Ω
3.3V 2A
C10 220µF 10V
QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA
2
11
12
14
PGATE
NGATESGND PGND
PDRIVE
RGND
AN54-13
Application Note 54
AN54 • F11A
C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC Q2 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE
ALL OTHER CAPACITORS ARE CERAMIC
VCC
VCC
CAP
SD2
ITH
CT
LTC1149
VIN
SENSE+VFB
SENSE–
D1 1N4148
+
C9 0.01µF
D4 1N4148
+
VIN 10V TO 48V C1
0.1µF
+ C4 1µF
R1 1k
Q3 2N3904
Q4 2N3906
33k
10k 33k
D3 5.1V
432k 1%
49.9k 1%C7
3300pF X7R
C8 200pF NPO
3
5
16
15
7
6
1 4
9
10
8
13
C3 0.047µF Z5U
Q1 IRF9Z34
Q2 IRFZ34
D2 MBR160
C2 330µF 63V
L1 62µH
R2 0.05Ω
VOUT 12V 2A
C10 220µF × 2 10V
QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 560mA
2
11
12
14
PGATE
NGATESGND PGND
PDRIVE
RGND
C5 0.1µF
C6 0.068µF
Z5U
10k
Figure 11A. LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter
LTC1149: (10V-48V to 12V/2A) High VoltageBuck Converter
The LTC1149 contains an internal 10V low dropout linearregulator to provide power to the control circuitry. Itactually means that the DC bias current as well as the gatecharge current come directly from the input line, causingslight efficiency degradation, especially for high inputvoltages (additional power is dissipated by the internalregulator). A solution for this problem is presented inFigure 11A. When the output level reaches about 5V, ZenerD3 starts conducting and saturates Q3, which in turnswitches Q4 on. Now VCC pins 3 and 5 are powered directlyfrom the output. Losses caused by DC current and gatecharge current are significantly reduced allowing im-proved efficiency at high input voltage.
The regulator output must be set up for an output voltageless than 14.5V to provide a margin for the LTC1149 pin5 absolute maximum rating of 16V. It should also be
observed that Q4 turns on when the output is less than 10V(the internal regulator output) and stays on or off under allconditions.
Figure 11B. LTC1149: (10V-48V to 5V/2A) MeasuredEfficiency with Large P-Channel and N-ChannelMOSFETs
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
65
600.01 0.1
AN54 • F11B
1 10
VIN = 15V
VIN = 48V
VIN = 36V
Application Note 54
AN54-14
LTC1149: High Power Buck Converters
Figures 12A and 13A are examples of high power (morethan 100W) converters that use the LT1149. The regula-tors are powered from the full wave rectified output of a16VRMS to 32VRMS transformer. Input capacitance is verybulky, but it has to ensure that ripple valleys do not dipbelow the minimum regulator input requirement. Thecircuit in Figure 13A has additional gate driver circuitswhich are required to improve MOSFET switching times.Overall efficiency goes as high as 98%! Remember, atthese output current levels layout becomes extremelyimportant, and all the recommendations from the LTC1149data sheet must be closely followed.
COUT, 1500µF 25V, × 2
PGATE
VIN
VCC
PDRIVE
VCC
CT
ITH
SENSE–
CAP
SD2
RGND
NGATE
PGND
SGND
VFB
SENSE+
SHUTDOWN (NORMALLY GND)
100pF
VIN 16VRMS RECTIFIED
+
+
10µF
0.33µF
0.33µF
R2 205k
100Ω
LTC1149
100Ω
3300pFCT
270pF
470Ω
RS 0.0082Ω
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
Q1 RFG60P06E
Q2 IRFZ44
D2 MBR380
D1 1N4148
AN54 • F12A
OUTPUT GROUND CONNECTION
L 33µH
1.5µF 63V WIMA
1µF WIMA
33k
VOUT 13.8V 10A
1000pF
COUT PANASONIC HFQ SERIES D2 MOTOROLA SCHOTTKY Q1 HARRIS PMOS BV DSS = 60V RDSON = 0.03Ω
0.22µF CIN
20000µF 35V
+
R1 20.5k 1%
Figure 12A. LTC1149: (16VRMS to 13.8V/10A) Buck Converter
OUTPUT CURRENT (A)0.01
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
650.1 1 10
AN54 • F12B
Figure 12B. LTC1149: (16VRMS to 13.8V/10A)Buck Converter Measured Efficiency
AN54-15
Application Note 54
COUT, 1000µF 35V
PGATE
VIN
VCC
PDRIVE
VCC
CT
ITH
SENSE–
CAP
SD2
RGND
NGATE
PGND
SGND
VFB
SENSE+
SHUTDOWN (NORMALLY GND)
100pF
VIN 32VRMS RECTIFIED
+
+
10µF
0.33µF
MPSW06
MPSA56
PDRIVE BUFFER
NDRIVE BUFFER
0.33µF
R2 432k
100Ω
LTC1149
100Ω
3300pFCT
150pF
470Ω
RS 0.016Ω
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
Q1 SMP40P06
Q2 IRFZ34
D2 MBR380
AN54 • F13A
OUTPUT GROUND CONNECTION
L 62µH
1N4148
D1 1N4148
1.5µF 63V WIMA
1µF WIMA
33k
VOUT 27.6V 5A
1000pF
0.22µF
CIN 5000µF 75V
+
R1 20.5k 1%
MPSA56
COUT PANASONIC HFQ SERIES D2 MOTOROLA SCHOTTKY Q1 SILICONIX PMOS BV DSS = 60V RDSON = 0.045Ω
Figure 13A. LTC1149: (32VRMS to 27.6V/5A) Buck Converter
OUTPUT CURRENT (A)0.01
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
650.1 1 10
AN54 • F13B
Figure 13B. LTC1149: (32VRMS to 27.6V/5A) Buck Converter Measured Efficiency
Application Note 54
AN54-16
LTC1147: (5V-14V to 5V/1A) Buck Converter withSurface Mount Technology
The LTC1147 (Figure 14A) is a great way to implement ahigh efficiency regulator using a minimum number ofexternal components and occupying the least board space.This regulator provides many advantages of the LTC1148including constant off-time configuration, low dropoutregulation and Bust Mode operation, comes in a smallerpackage and does not require the N-channel MOSFET. Theonly sacrifice made is synchronous rectification whichdegrades the efficiency of this circuit up to three percent-age points. Compare efficiency graphs in Figures 1B and14B! Since the clamp diode D1 conducts all the timeduring the off-time, a larger diode (MBRD330) is used forthis circuit. The LTC1147 is an excellent choice where theoutput current is less than 1A, and where the input voltageis less than twice the output voltage.
Figure 14B. LTC1147: (5V-14V to 5V/1A)Buck Converter Measured Efficiency
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 1
AN54 • F14B
60
VIN = 6V
VIN = 10V
VIN = 14V
AN54 • F14A
C2 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C5 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL SP-1/2-A1-0R100J Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE
ALL OTHER CAPACITORS ARE CERAMIC
ITH
CT
GND
LTC1147-5
VIN
SENSE +
SENSE –
+
C5 0.001µF
+
VIN 5V TO 14V
R1 1k
C3 3300pF X7R
C4 390pF NPO
2
8
5
4
Q1 Si9430DY
D1 MBRD330
C2 22µF x 2 25V
100µH
R2 0.1Ω
5V 1A
C6 220µF 10V
QUIESCENT CURRENT = 190µA TRANSITION CURRENT (Burst Mode OPERATION/ CONTINUOUS OPERATION) = 170mA
1
7
SHUTDOWN6
+
L1
1
2
4
3
C1 0.1µF
3
PDRIVE
Figure 14A. LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology
AN54-17
Application Note 54
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 1
AN54 • F15B
60
VIN = 5V
VIN = 10V
VIN = 14V
Figure 15B. LTC1147: (4V-14V to 3.3V/1A)Buck Converter Measured Efficiency
LTC1147: (4V-14V to 3.3V/1A) Buck Converter withSurface Mount Technology
Figure 15A shows another compact circuit with theLTC1147 series. It generates 3.3V/1A output using thesame configuration as in the previous example. Despitethe lack of synchronous rectification, efficiency approaches95% with 5V input.
AN54 • F15A
C2 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C6 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX BVDSS = 20V DCRON = 0.100Ω CRSS = 400pF Qg = 50nC D1 MOTOROLA R2 KRL SP-1/2-A1-0R100 Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE
ITH
CT
GND
LTC1147-3.3
VINPDRIVE
SENSE +
SENSE –
+
C5 0.001µF
+
VIN 4V TO 14V
R1 1k
C3 3300pF X7R
C4 560pF NPO
2
8
5
4
Q1 Si9430DY
D1 MBRD330
C2 22µF × 2 25V
100µH
R2 0.1Ω
3.3V 1A
C6 220µF 10V
QUIESCENT CURRENT = 170µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 170mA
1
7
SHUTDOWN6
+
L1
1
2
4
3
C1 0.1µF
3
Figure 15A. LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology
Application Note 54
AN54-18
LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter withSurface Mount Technology
One more application circuit with LTC1147 is presented inFigure 16A. It is optimized for 5V to 3.3V conversion withinput voltages of 4V to 8V (limited by the P-channelMOSFET). A circuit board has been laid out for this circuitand has subsequently been thoroughly tested under fulloperating conditions and optimized for mass productionrequirements. A Gerber file for the board is available uponrequest.
AN54 • F16A
C1 AVX TPSD476M016R0150 TANTALUM 47µF 16V C6 AVX TPSD107M010R0100 TANTALUM 100µF 10V D1 MOTOROLA MBRS130LT3 BVR = 30V L1 SUMIDA CDR74B-100LC 10 µH Q1 SILICONIX PMOS Si9433 R2 IRC LRC-LR2010-01-R068-F
ALL OTHER CAPACITORS CERAMIC
ITH
CT
GND
LTC1147-3.3
VINPDRIVE
SENSE +
SENSE –
+
C5 0.01µF
+
VIN 4V TO 8V
0V = NORMAL ≥ 2V = SHUTDOWN
R1 1k
C3 3300pF
C4 120pF
2
8
5
4
D1 MBRS130LT3
C1 47µF 16V
R2 0.068Ω
VOUT 3.3V 1.5A
C6 100µF 10V
1
7
SHUTDOWN6
L1 10µH
C2 0.1µF
3
Q1 P-CH
Si9433DY
Figure 16A. LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
65
600.01 0.1 1
AN54 • F16B
LTC1147-3.3 SUMIDA CDR74B
VIN = 5V
LTC1147-3.3 SUMIDA CD54
VIN = 5V
2
Figure 16B. LTC1147: (4V-8V to 3.3/1.5A)Buck Converter Measured Efficiency
AN54-19
Application Note 54
LTC1148: (10V-14V to 5V/10A) High CurrentBuck Converter
Due to differences in physical structure between N- and P-channel MOSFETs, the former are usually more costeffective, more available, and provide better internal pa-rameters for the same size. This is especially importantwhen high output currents are required. With 5A to 10Aoutput currents the use of N-channel MOSFETs in place ofP-channel is the most preferable solution. An implemen-tation of this idea is presented in Figure 17A.
A special Q4 gate drive circuit that uses a bootstrappingtechnique is added to provide required gate drive. Whenpin 1 goes high it turns Q3 on, providing a path for fast Q4gate capacitance discharge. With Q3 off, Q1 and Q2saturate each other feeding positive voltage to Q4’s gate.As a result Q4 turns on, and the positive pulse at its sourceis AC coupled through C6 supplying bootstrapped VCC forthe gate drive “SCR.” The external driver circuit contains
only inexpensive, readily available small-signal transis-tors, yet allows the use of all N-channel MOSFETs. Effi-ciency reaches 96% (see Figure 17B).
OUTPUT CURRENT (A)0.1
50
EFFI
CIEN
CY (%
)
70
80
90
100
1 10
AN54 • F17B
60
VIN = 10V
VIN = 14V
Figure 17A. LTC1148: (10V-14V to 5V/10A) High Current Buck Converter
Figure 17B. LTC1148: (10V-14V to 5V/10A) High CurrentBuck Converter Measured Efficiency
Q4 IRFZ44
AN54 • F17A
C1 (Ta) C7 UNITED CHEMI-CON (Al) LXF35VB272M16 X 40 ESR = 0.018Ω IRMS = 2.900A C8 NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A Q4, Q5 IR NMOS BVDSS = 60V DCRON = 0.028Ω CRSS = 310pF Qg = 69nC D1, D2 MOTOROLA SILICON VBR = 75V D3 MOTOROLA SCHOTTKY VBR = 30V
ITH
CT
SGND PGND
LTC1148-5
VINPDRIVE
SENSE +
SENSE –
NDRIVE
C5 0.001µF
+
VIN 10V TO 14V
C1 1µF
R4 1k
C3 3300pF X7R
C4 820pF NPO
10
4
1
8
7
14
Q5 IRFZ44
D3 1N5818
C6 0.47µF
R8 0.01Ω
5V 10A
C8 2200µF × 3 16V
3
11
12
SHUTDOWN
6
C2 0.1µF
+
Q3 VN2222LL
D1 1N4148
R1 20k
Q1 2N3906
Q2 2N2222
+ C7 2700µF × 2 35V
R6 100
D2 1N4148
R3 220
L1
33µH
R7 22k
R2 220
R5 100
R8 KRL NP-2A-C1-0R010J Pd = 3W L1 COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE
ALL OTHER CAPACITORS ARE CERAMIC
QUIESCENT CURRENT = 22mA
Application Note 54
AN54-20
Two resistors are placed in series with the current sensepins. This significantly improves circuit noise immunitywhich is of great importance when switching high current.R7, connected between pin 7 and ground, disables BurstMode operation so that the regulator operates continuously.
LTC1149: (12V-36V to 5V/5A) High Current, HighVoltage Buck Converter
Figure 18A shows a high current, high voltage buckconverter. The LTC1149 is used to accommodate the inputvoltage requirement. As in Figure 17A the top N-channelMOSFET is driven by an external circuit which inverts thechip’s P-drive output and uses bootstrapping to providepositive gate-source voltage. The peak-to-peak gate volt-age is defined by the DC portion of the gate driver VCC.Therefore, not to exceed maximum gate voltage for theMOSFET, D1’s anode is connected to internal 10V regula-tor output. In this application PDRIVE pin 4 is used because
an output referenced to ground is required. PGATE pin 1provides the same drive signal referenced to VCC.
Figure 18B. LTC1149: (12V-36V to 5V/5A) High Current, HighVoltage Buck Converter Measured Efficiency
OUTPUT CURRENT (A)0.1
50
EFFI
CIEN
CY (%
)
70
80
90
100
1 5
AN54 • F18B
60
VIN = 12V
VIN = 24V
VIN = 36V
Figure 18A. LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter
Q4 MTP30N06EL
AN54 • F18A
C6 0.001µF
+
C7 0.22µF
R7 0.02Ω
5V 5A
C9 220µF × 2 10V
Q3 VN2222LL
D1 1N4148
R2 10k
Q1 2N3906
Q2 2N2222
C8 1000µF 63V
D2 1N4148
R4 220Ω
L1
50µH
R3 220Ω
VCC
VCC
CAP
SD1
SD2
ITH
CT
LTC1149-5
PGATE
VIN
SENSE +
SENSE –
NGATE
VIN 12V TO 36V
C1 0.1µF
+ C2 1µF
C3 0.1µF
R1 1k
C4 3300pF
X7R
C5 820pF NPO
3
5
16
10
15
7
6
4
9
8
13
2
11
12
14
SGND PGND
PDRIVE
RGND
Q5 IRFZ34
D3 MBR160
C2 (Ta) C8 NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A C9 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 PNP BV CEO = 30V Q2 NPN BVCEO = 40V Q3 SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω Q4 MOTOROLA NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 40nC
R6 100Ω
R5 100Ω
+
1
Q5 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC D1, D2 SILICON VBR = 75V D3 MOTOROLA SCHOTTKY VBR = 60V R7 KRL NP-2A-C1-0R020J Pd = 3W L1 COILTRONICS CTX50-5-52 DCR = 0.021Ω #52 IRON POWDER CORE
ALL OTHER CAPACITORS ARE CERAMIC
AN54-21
Application Note 54
LTC1149: (12V-48V to 5V/10A) High Current, HighVoltage Buck Converter
The circuit in Figure 19A uses the same configuration butis designed to provide up to 10A output current. Besidesthe usual external component changes, the circuit useshigher current MOSFETs to improve efficiency at maxi-mum power levels. Efficiency at 5A output is severalpercentage points better than in the previous example(compare Figures 18B and 19B). R7 keeps the regulator incontinuous mode causing the rapid efficiency decrease atlighter loads.
Figure 19B. LTC1149: (12V-48V to 5V/10A) High Current,High Voltage Buck Converter Measured Efficiency
OUTPUT CURRENT (A)0.1
50
EFFI
CIEN
CY (%
)
70
80
90
100
1 10
AN54 • F19B
60
VIN = 12V
VIN = 48V
VIN = 36V
VIN = 24V
Q4 IRFZ34
AN54 • F19A
C6 0.001µF
+
C7 0.22µF
R8 0.01Ω
5V 10A
Q3 VN2222LL
D1 1N4148
R2 20k
Q1 2N3906
Q2 2N2222
C8 1000µF × 2 63V
D2 1N4148
R4 220Ω
L1
33µH
R3 220Ω
VCC
VCC
CAP
SD1
SD2
ITH
CT
LTC1149-5
PGATE
VIN
SENSE +
SENSE –
NGATE
VIN 12V TO 48V
C1 0.1µF
+ C2 1µF
C3 0.1µF
R1 1k
C4 3300pF
X7R
C5 820pF NPO
3
5
16
10
15
7
6
1
4
9
8
13
2
11
12
14
SGND PGND
PDRIVE
RGND
Q5 IRFZ44
D3 MBR160
C2 (Ta) C8 NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A C9 NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A Q1 PNP BVCEO = 30V Q2 NPN BVCEO = 40V Q3 SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω Q4 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC Q5 IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC
R6 100Ω
R5 100Ω
+
R7 22k
QUIESCENT CURRENT = 26mA
+
C9 220µF × 3 16V
D1, D2 SILICON VBR = 75V D3 MOTOROLA SCHOTTKY VBR = 60V R8 KRL NP-2A-C1-0R010J Pd = 3W L1 COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE
ALL OTHER CAPACITORS ARE CERAMIC
Figure 19A. LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter
Application Note 54
AN54-22
Figure 20A. LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter
9
8
Q4 IRFZ44
AN54 • F20A
C7 0.001µF
C7 0.22µF
24V 10A
C10 1000µF × 3 35V
Q3 VN2222LL
D1 IN4148
R3 20k
Q1 2N5087
Q2 MPS651
C8 1000µF × 2 63V
D2 1N4148
R2 5.1k
L1
50µH
VCC
VCC
CAP
SD2
ITH
CT
LTC1149
PGATE
VIN
VFB
SENSE +
NGATE
VIN 32V TO 48V
C1 0.1µF
+ C2 1µF
C3 0.1µF
R1 1k
C4 3300pF
X7R
C5 270pF NPO
3
5
16
15
7
6
4
10
13
2
11
12
14
SGND PGND
PDRIVE
RGND
Q5 IRFZ44
C2 (Ta) C9 NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A C10 NICHICON (Al) UPL1V102MRH ESR = 0.029Ω IRMS = 1.980A Q4, Q5 IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC Q1 PNP BVCEO = 50V Q2 NPN BVCEO = 60V D1, D2, D3, D4 SILICON VBR = 75V D5 MOTOROLA SCHOTTKY VBR = 60V R10 KRL NP-2A-C1-0R010J Pd = 3W L1 COILTRONICS CTX50-10-KM DCR = 0.010Ω Kool Mµ CORE
ALL OTHER CAPACITORS ARE CERAMIC
100Ω
R6 100Ω
+
SENSE –
1
C6 100pF
R8 220k 1%
R5 220Ω
D3 1N4148
R4 220Ω
D4 1N4148
R9 12k 1%
D5 MBR160
R10 0.01Ω
R7
VOUT = 1.25V (1 + R8/R9) QUIESCENT CURRENT = 26mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 1.5A
+
+
R11 39k
LTC1149: (32V-48V to 24V/10A) High Current, HighVoltage Buck Converter
If an output voltage other than 5V or 3.3V is required, anadjustable version of the regulator must be used. A 24V/10A example is shown in Figure 20A. The output voltageis set by resistors R8 and R9. The LTC1149 monitors VFB(pin 10) keeping it at 1.25V. Similar to the previous twocircuits, an external gate driver is added to switch theN-channel MOSFET Q2. To ensure consistent start-up ofthe bootstrapping circuitry, the driver is initially poweredby R2 and D2. (The main requirement at start-up is tosupply the driver with VCC that exceeds output targetvoltage.) After the switching starts, D1 an D3 power theexternal gate drive circuit.
OUTPUT CURRENT (mA)10
50
EFFI
CIEN
CY (%
)
70
80
90
100
100 1A 10A
AN54 • F20B
60
VIN = 32V
VIN = 45V
Figure 20B. LTC1149: (32V-48V to 24V/10A) High Current,High Voltage Buck Converter Measured Efficiency
AN54-23
Application Note 54
LT1148: (4V-14V to 5V/1A) SEPIC Converter
Figure 21A provides the function of a step-up and step-down converter without using a transformer. This topol-ogy is called a SEPIC converter. The P-channel transistorand L1 are arranged similarly to a buck-boost topologyproviding the boost part of the regulator. Pulses at Q2’sdrain (actually two paralleled devices) are coupled via C8to the buck portion that includes Q3 and L2. This circuitaccepts 4V to 14V input and provides a solid 5V output.Even though the schematic shows two inductors, theycarry the same current and can be wound on a single core.Such dual coils are readily available (see circuit parts list).This topology is acceptable for moderate loads only, as thecoupling capacitor C8 carries the full load current andmust be sized accordingly. When the sense resistor isplaced at ground potential, such as the case in this circuit,the off-time increases approximately 40%.
An adjustable version of the regulator is required when the
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 1
AN54 • F21B
60
VIN = 14V
VIN = 4V
VIN = 5V
VIN = 4V
VIN = 10V
VIN = 5V
current sense resistor is placed at ground. This allows toprovide different output voltages. D2 is included for foldbackshort-circuit protection. When VOUT equals zero (output isshorted) D2 clamps pin 6 and limits the output current.
Figure 21B. LTC1148: (4V-14V to 5V/1A)Buck-Boost Converter Measured Efficiency
Figure 21A. LTC1148: (4V-14V to 5V/1A) SEPIC Converter
AN54 • F21A
C6 0.1µF
VOUT 5V 1A
C10 220µF 10V
Q2 Si9430DY x 2
C7 100µF 20V
VIN 4V TO 14V C1
1µF
C2 0.1µF
R1 1k
C4 3300pF
X7R
C5 390pF NPO
5
10
6
4
1
9
8
7
D2 MBR0520L
14
3
11
12
D1 1N5818
C1 (Ta) C7 SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A C8, C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q2 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q3 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL NP-1A-C1-0R082J Pd = 1W L1 COILTRONICS CTX50-4P, CTX50-5P
ALL OTHER CAPACITORS ARE CERAMIC
+
R2 0.082Ω
TO VOUT
SHUTDOWN
ITH
CT
LTC1148
PDRIVE
VIN
SENSE +
NDRIVESGND PGND
VFB
SENSE –
INT VCC
C8 220µF 10V
L1 50µH
Q3 Si9410DY
R3 75k 1%
R4 25k 1%
+
C9 100pF
+ +
L2 50µH
VOUT = 1.25V (1 + R3/R4) QUIESCENT CURRENT = 200µA TRANSITION CURRENT (Burst Mode OPERATION/ CONTINUOUS OPERATION) = 250mA/VIN = 5V
Application Note 54
AN54-24
OUTPUT CURRENT (A)0.001
50
EFFI
CIEN
CY (%
)
70
80
90
100
0.01 0.1 0.5
AN54 • F22B
60
VIN = 14V VIN = 4V
VIN = 10V VIN = 5VLTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A)Split Supply Converter
Applications requiring a split supply can use the circuitpresented in Figure 22A. It contains the converter fromFigure 21A and adds a synchronous charge pump Q4 toprovide a –5V output. Q4 source is referenced to the –5Vline, and its gate drive is AC coupled via C11 and clampedby D3. The outputs exhibit excellent tracking with line andload changes. This is a great way to build a dual outputconverter without any transformer.
SENSE –
AN54 • F22A
C7 0.1µF C10
220µF 10V
Q2 Si9430DY
C8 100µF 20V
VIN 4V TO 14V C1
1µF
C2 0.1µF
R1 1k
C4 3300pF
X7R
C5 390pF NPO
5
10
6
4
1
8
7
9
14
3
11
12
D1 1N5818
C1 (Ta) C8 SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A C9, C10, C12 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q2 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q3, Q4 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1, D2 MOTOROLA SCHOTTKY VBR = 30V R2 KRL NP-1A-C1-0R082J Pd = 1W L1 COILTRONICS CTX50-4
+
R2 0.05Ω
VOUT
SHUTDOWN
ITH
CT
LTC1148
PDRIVE
VIN
SENSE +
NDRIVESGND PGND
VFB
INT VCC
C9 220µF 10V
L1 50µH
Q3 Si9410DY
R3 75k 1%
R4 25k 1%
C11 0.22µF
+ +
L2 50µH
VOUT = 1.25V (1 + R3/R4) QUIESCENT CURRENT = 250µA TRANSITION CURRENT (DIS/CONT) = 130mA/VIN = 5V
C6 100pF
R5 51k
D3 1N4148
C12 220µF 10V
–VOUT –5V 0.5A
+VOUT 5V 0.5A
+
+
Q4 Si9410DY
D2 1N5818
D4 MBR0520L
Figure 22A. LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter
Figure 22B. LTC1148: (4V-14V to 5V/0.5A, –5V/0.5A)Split Supply Converter Measured Efficiency
AN54-25
Application Note 54
LTC1148: (4V-10V to –5V/1A) Positive-to-NegativeConverter
Figure 23A shows a buck-boost converter using theLTC1148. This is an inverting topology, and it can inher-ently buck or boost the input voltage. Ground pins of thechip are referenced to the output line; no additional levelshifting circuit is required to drive the N-channel FET Q3(its source is referenced to – 5V as well). Now even withminimum input level, the circuit provides a solid 9V peak-to-peak MOSFET drive signal. However, so as not toexceed absolute maximum voltage at pin 3, the input lineis limited to 10V. If the circuit is required to accept a higherinput voltage, the LTC1148HV can be used instead. Q1 isadded to provide a logic level shutdown feature. If shut-down is not needed omit Q1 and R1, and short pin 10 topin 11.
Figure 23A. LTC1148: (4V-10V to –5V/1A) Positive-to-Negative Converter
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
65
600.01 0.1
AN54 • F23B
1 10
4V TO –5V/1A
10V TO –5V/1A
Figure 23B. LTC1148: (4V-10V to – 5V/1A)Positive-to-Negative Converter MeasuredEfficiency
SENSE –
AN54 • F23A
C5 0.01µF
C8 220µF × 2 10V
Q2 Si9430DY
C7 150µF × 2 16V
VIN 4V TO 10V
C1 1µF
C2 0.1µF
R2 1k
C3 6800pF
X7R
C4 560pF NPO
5
10
6
4
1
8
7
9 14
3
11
12
D1 1N5818
C1 (Ta) C7 SANYO (OS-CON) 16SA150M ESR = 0.035Ω IRMS = 2.280A C8 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q2 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q3 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL NP-1A-C1-0R050J L1 COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE
ALL OTHER CAPACITORS ARE CERAMIC
+
R2 0.05Ω
Q1 TP0610L
SHUTDOWN
ITH
CT
LTC1148
PDRIVE
VIN
SENSE +
NDRIVESGND PGND
VFB
INT VCC
L1 50µH
Q3 Si9410DY
R3 75k 1%
R4 25k 1%
+
VOUT = 1.25V (1 + R3/R4)
C6 200pF
– 5V 1A
+ R1 1M
SHUTDOWN
Application Note 54
AN54-26
LTC1148: (5V-12V to –15V/0.5A) Buck-BoostConverter
Figure 24A presents an inverting regulator designed toaccommodate higher output voltages. The LTC1148 can-not accept feedback directly from a negative output. Toregulate negative outputs, the feedback must be invertedand compared against 1.25V. This function is provided bya DC level shifting amplifier consisting of Q1 and associ-ated components. Resistor R4 provides amplifier negativefeedback, effectively cancelling variations in VCC, and Q2provides temperature compensation. The output voltageis set by resistors R4 and R5. As usual, with the senseresistor at ground potential, the off-time increases roughlyby 40%.
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
95
90
85
80
75
70
650.01 0.1 1
AN54 • F24B
5V TO –15V/0.5A
12V TO –15V/0.5A
Figure 24B. LTC1148: (5V-12V to –15V/0.5A)Buck-Boost Converter Measured Efficiency
AN54 • F24A
C8 0.01µF
C9 47µF 25V
Q3 Si9435DY × 2
C7 220µF 10V
C6 200pF
C5 6800pF
10
6
4
11
1
8
7
9
12
3
U1
D3 MBR735
R7 DALE LVR-3 0.033W L1 COILTRONICS CTX50-5-52 C7 SANYO OS-CON 105A220K C9, C10 SANYO OS-CON 255C47K
+
R7 0.033Ω
Q2 2N5210
Q1 2N5210
LTC1148
VIN
SHUTDOWN
ITH
CT
SGND
PDRIVE
SENSE+
SENSE–
VFB
PGND
L1 50µH
R4 49.9k 1%
+
+ C10 47µF 25V
C2 0.1µF
C3 1µF
C11 200pF
R6 1k
R3 56k
> 1.5V = SHUTDOWN
R5 634k 1%
VOUT –15V 0.5A
VIN 5V TO 12V
+
Figure 24A. LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter
AN54-27
Application Note 54
LTC1148: (2V-5V to 5V/1A) Boost Converter
Even though the LTC1148 is mainly used in step-downconverters, it can also show excellent performance in theboost configuration. A boost implementation is shown inFigure 25A. This is a two-cell to 5V converter that uses theLT1109 to provide 12V to power the main regulator chip(unfortunately, MOSFETs do not operate with only 2V at thegate). The LT1109 is a small micropower IC that requiresonly three external components and provides great effi-ciency. An N-channel transistor is used as the switch, andgeneral purpose MOSFETs Q1 and Q2 are used to form aninverting gate driver. When Q3 turns off, the voltage at itsdrain rises above VIN, and a Schottky diode D2 startsconducting. In a short period of time Q4 shorts it outproviding a synchronous rectification feature and increas-ing efficiency. If 12V is already available, the LT1109 can beomitted and the 12V line connected directly to pin 3.
Figure 25A. LTC1148: (2V-5V to 5V/1A) Boost Converter
Q1 TP0610L
SENSE –
AN54 • F25A
C6 0.001µF
C8 220µF × 2 10V
VIN 2V TO 5V
C1 100µF 10V
R2 1k
C4 6800pF
X7R
C5 390pF NPO
10
6
4
1
12V
8
7
9
14
3
11
12
D2 1N5818
C1 SANYO (OS-CON) 10SA100M ESR = 0.045Ω IRMS = 1.870A C3 (Ta) C8 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q3, Q4 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1, D2 MOTOROLA SCHOTTKY VBR = 30V
SHUTDOWN
ITH
CT
LT1109
PDRIVE
VIN
SENSE +
NDRIVESGND PGND
VFB
L1 33µH
Q2 VN2222LL
R3 75k 1%
+
C7 100pF
5V 1A
R1 0.05Ω
VIN
SENSE
GND
S/D7
3
1
4
8
D1 1N5818
SHUTDOWN
C2 0.1µF
C3 1µF
+
Q3 Si9410
L2 25µH
R4 25k 1%
Q4 Si9410
+
SW
LTC1148
VR1
R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX33-1 DCR = 0.220Ω Kool Mµ CORE L2 COILTRONICS CTX25-4
VOUT = 1.25V (1 + R3/R4)
Figure 25B. LTC1148: (2V-5V to 5V/1A)Boost Converter Measured Efficiency
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
650.01 0.1 1
AN54 • F25B
4V TO 5V/1A
2V TO 5V/1A
Application Note 54
AN54-28
LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)Dual Buck Converter
A circuit that provides dual 3.3V/5V output is shown inFigure 26A. It uses a dual LTC1143 regulator that com-bines two LTC1147, non-synchronous switching regula-tors. The efficiency was measured with only one outputloaded which provided worse results for low output cur-rent due to the presence of the second half’s quiescentcurrent. This circuit provides very simple means to powerdual voltage logic. It occupies small amount of boardspace and is very efficient! OUTPUT CURRENT (A)
0.001
EFFI
CIEN
CY (%
)
95
90
85
80
75
70
65
600.01 0.1
AN54 • F26B
1 10
14V TO 3.3V
8V TO 5V
8V TO 3.3V
14V TO 5V
Figure 26B. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)Dual Buck Converter Measured Efficiency
+
+ +
PDRIVE3
SENSE+ 3
SENSE– 3
GND3 GND5CT3 ITH3 ITH5 CT5
SENSE– 5
SENSE+ 5
PDRIVE5
VIN3 SHUTDOWN 5 VIN5
LTC1143
CT5 200pF
CT3 390pF
3 14 15 7 6 11
RC5 1k
CC3 3300pF
CC5 3300pF
RC3 1k
13 10 5
12
9
8
4
1
16
VOUT5 5V/2A
COUT5 220µF 10V × 2
RSENSE5 0.05Ω
L2 20µH
D2 MBRD330
RSENSE: KRL SL-1R050J L1, L2: COILTRONICS CTX20-4 CIN3, CIN5: AVX (Ta) TPSD226K025R0200 COUT3, COUT5: AVX (Ta) TPSE227K010R0080 Q1, Q2: SILICONIX PMOS Si9430DY
D1 MBRD330
0V = NORMAL >1.5V = SHUTDOWN
CIN5 22µF 25V × 2
CIN3 22µF 25V × 2 Q1
P-CH Si9430DY
COUT3 220µF 10V × 2
L1 20µH
RSENSE3 0.05ΩVOUT3
3.3V/2A
VIN 5.2V TO 14V
+
Q2 P-CH
Si9430DY
0.01µF 0.01µF
AN54 • F26A
0.22µF0.22µF
SHUTDOWN 32
Figure 26A. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter
AN54-29
Application Note 54
Figure 27B. LTC1148HV-5: (5.2V-18V to 5V/1A) HighVoltage Buck Converter Measured Efficiency
LTC1148HV-5: (5.2V-18V to 5V/1A) High VoltageBuck Converter
The standard LTC1148 input voltage is limited to 16Vabsolute maximum level, which is not sufficient in someapplications. Figure 27A shows a step-down regulatorusing the high voltage LTC1148HV. It contains the sameinternal functions but accepts up to 20V input (remember,MOSFET’s gates are usually rated at 20V maximum). As abuilding block it can be used in the same manner asLTC1148. Input tantalum capacitors now have to be ratedat 35V to ensure reliable operation under maximum inputvoltage.
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
65
60
550.01 0.1 1
AN54 • F27B
7V TO 5V
12V TO 5V
18V TO 5V
1
2
3
4
5
6
7
14
13
12
11
10
9
8
PDRIVE
NC
VIN
CT
INT VCC
ITH
SENSE–
NDRIVE
NC
PGND
SGND
SHUTDOWN
NC
SENSE+
LTC1148HV-5
+ 1µF
1000pF R1 0.1Ω
SHUTDOWN
L1 50µH
Q2, Si9410DY
D1 MBRS140T3
Q1 Si9430DY
+ CIN 10µF 35V × 2
VIN 5.2V TO 18V
+COUT 220µF 10V AVX
VOUT 5V/1A
CC 3300pF
RC 1k
CT 220pF
CIN COUT L1 R1 Q1 Q2
AVX (Ta) TPSD106K035R0300 AVX (Ta) TPSE227K010R0080 COILTRONICS CTX50-4 KRL SP-1/2-A1-0R100 SILICONIX PMOS Si9430DY SILICONIX NMOS Si9410DY
AN54 • F27A
Figure 27A. LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter
Application Note 54
AN54-30
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
65
600.01 0.1 1
AN54 • F28B
18V to 3.3V
4V to 3.3V
12V to 3.3V
Figure 28B. LTC1148HV-3.3: (4V-18V TO 3.3V/1A)High Voltage Buck Converter Measured Efficiency
LTC1148HV-3.3 (4V-18V to 3.3V/1A) High VoltageBuck Converter
Figure 28A: Here is a high voltage version of the circuitshown in Figure 4A with input voltage increased to 18V.
1
2
3
4
5
6
7
14
13
12
11
10
9
8
PDRIVE
NC
VIN
CT
INT VCC
ITH
SENSE–
NDRIVE
NC
PGND
SGND
SHUTDOWN
NC
SENSE+
LTC1148HV-3.3
+ 1µF
1000pF 0.1Ω
SHUTDOWN
L1 50µH
Q2, Si9410DY
D1 MBRS140T3
Q1 Si9430DY
+ CIN 22µF 35V × 2
VIN 4V TO 18V
+COUT 220µF 10V
VOUT 3.3V/1A
CC 3300pF
RC 1k
CT 270pF
CIN COUT L1 R1 Q1 Q2
AVX (Ta) TPSE226K035R0300 AVX (Ta) TPSE227K010R0080 COILTRONICS CTX50-4 Kool Mµ CORE IRC LR2010-01-R100-G SILICONIX PMOS Si9430DY SILICONIX NMOS Si9410DY
AN54 • F28A
Figure 28A. LTC1148HV-3.3: (4V-18V to 3.3V/1A)High Voltage Buck Converter
AN54-31
Application Note 54
LTC1148HV: (12.5V-18V to 12V/2A) High VoltageBuck Converter
Figure 29A is another application of the LTC1148HV whichis configured as a step-down converter to provide 12V/2Aoutput. With this low dropout regulator, the input can goas low as 12.5V and still produce a regulated output.Resistors R2 and R3 set the output voltage level.
OUTPUT CURRENT (A)0.001
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
65
600.01 0.1
AN54 • F29B
1 10
Figure 29B. LTC1148HV: (16V to 12V/2A) High VoltageBuck Converter Measured Efficiency
C1 (Ta) C7 SANYO (OS-CON) 16SA150M Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX47-5P
ITH
CT
LTC1148HV
VIN
SENSE +
SENSE –
+
C6 0.01µF
100pF
+
VIN 12.5V TO 18V
C1 1µF
R1 1k
C4 3300pF X7R
C5 150pF NPO
10
4
1
8
7
9
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
C3 22µF x 2 35V
47µH
R2 0.05Ω
432k 1%
12V 2A
C7 150µF × 3 16V
3
11
12
SHUTDOWN
6
C2 0.1µF
+
AN54 • F29A
SGND PGND
PDRIVE
VFB
NDRIVE
49.9k 1%
Figure 29A. LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter
Application Note 54
AN54-32
Figu
re 3
0A. L
TC11
42: (
6.5V
-14V
to 3
.3V/
2A, 5
V/2A
, 12V
/0.1
5A) T
riple
Out
put B
uck
Conv
erte
r
AN
54 •
F30
A
2SH
UTDO
WN3
25C T
327
I TH3
26IN
T V C
C3
16SH
UTDO
WN5
11C T
513
I TH5
12IN
TVCC
55
NC
4P G
ND3
22NC
23P D
RIVE
37
NC6
N DRI
VE3
1SE
NSE+ 3
28SE
NSE– 3
9P D
RIVE
521
NC20
N DRI
VE5
15SE
NSE+ 5
14SE
NSE– 5
8NC
18P G
ND5
19NC
S GND
3S G
ND5
V IN5
V IN3
173
2410
LTC1
142
C4
3300
pF R8
510Ω
C17
200p
F 50
V
C1
3300
pF
R7
510Ω
C16
390p
F 50
V
C14
1µF
50V
C15
1µF
50V
C19
1000
pF
R5
18k
SHDN
4NC
46
NC6
7NC
7
V OUT
ADJ
215
V IN
GND
LT11
21CS
8C1
0 20
pF
R3
649k
1% R4
29
4k
1%
Q1
VN70
02
1 2
3
38
C9
22µF
25
V
+
Q3
Si94
10DY
D2
MBR
S140
+C6
22
µF
25V
+C7
22
µF
25V
R2
100Ω R1
10
0Ω
R10
0.04
0Ω
+C2
0 22
0µF
10V
+C2
1 22
0µF
10V
109
87
12
34
D3
MBR
S140R6
22
C13
1000
pF
C5
0.1µ
F
30µH
, 2A
LPE-
6562
-A02
6
+C8
22
µF
35V
Q5
Si94
10DY
D1
MBR
S140
+C2
22
µF
25V
+C3
22
µF
25V
32
41
L1
33µH
2A
CT
X33-
4
+C1
1 10
0µF
10V
R9
0.05
0Ω
+C1
2 10
0µF
10V
+ –
+ –
12V
ENAB
LE
–VIN
SHUT
DOW
N (T
TL IN
PUT)
SHUT
DOW
N (T
TL IN
PUT)
+VIN
6.
5V T
O 14
VQ4
Si
9430
DY
Q2
Si94
30DY
4
0V =
12V
OFF
>3
V =
12V
ON
(6V
MAX
) DO
NOT
FLO
AT
C18
2200
pF
T16 51.
8T SHUT
DOW
N PI
NS 2
AND
16
MUS
T AC
TIVE
LY B
E DR
IVEN
EI
THER
HIG
H OR
LOW
AND
NOT
ALL
OWED
TO
FLOA
T.
+ –
3.3V
/2A
12V/
150m
A
C2, C
3, C
6, C
7, C
9 C1
1, C
12
C20,
C21
L1
AVX
(Ta)
TPS
D226
M02
5R02
00
AVX
(Ta)
TPS
D107
K010
R010
0 AV
X (T
a) T
PSE2
27M
010R
0100
CO
ILTR
ONIC
S CT
X33-
4
R9
R10
T1
IRC
LR25
12-R
050
IRC
LR25
12-R
040
DALE
, LPE
-656
2-AO
26
5V/2
A
AN54-33
Application Note 54
LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A)Triple Output Buck Converter
LTC1142 is a dual output synchronous switching regula-tor controller. Two independent controller blocks(LTC1148-based) simultaneously provide 3.3V and 5Voutputs. The circuit in Figure 30A shows an application ofthis IC; it generates triple output voltages with 12V forflash memory programming in addition to the usual logicpower levels. The 3.3V section is a regular buck convertercircuit, the 5V section contains an off-the-shelf trans-former T1 in place of the inductor. The secondary windingis used to boost the output level which is rectified andregulated by an LT1121 to provide a clean and stable 12Voutput. A turns ratio of 1:1.8 is used to ensure that theinput voltage to the LT1121 is high enough to keep theregulator out of dropout. With LTC1142 synchronousswitching, the auxiliary 12V output may be loaded withoutregard to the 5V primary output load as long as the loopremains in continuous operation mode. Continuous op-eration is ensured by R5 which inhibits Burst Modewhenever the 12V output is enabled (enable line goeshigh). Make sure that the enable lines are not floating andare driven by TTL level signals. A circuit board has beenlaid out for this circuit and has subsequently been thor-oughly tested under full operating conditions and opti-mized for mass production requirements. A Gerber file forthe board is available upon request.
OUTPUT CURRENT (A)0.001
60
EFFI
CIEN
CY (%
)
65
100
0.01 2.5
AN54 • F30B
0.1
80
1
90
70
75
85
95
LTC1142-3.3 VIN = 8V
LTC1142-5 VIN = 8V
Figure 30B. LTC1142:(6.5V-14V to 3.3V/2A, 5V/2A,12V/0.15A) Triple Output Buck ConverterMeasured Efficiency
Application Note 54
AN54-34
LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A)High Voltage Triple Output Buck Converter
Figure 31A shows the same configuration as Figure 30Ausing the high voltage LTC1142HV. Circuit operation isidentical, but now it can accept up to 18V at the input.
OUTPUT CURRENT (A)0.001
60
EFFI
CIEN
CY (%
)
65
100
0.01 2.5
AN54 • F30B
0.1
80
1
90
70
75
85
95
LTC1142-3.3 VIN = 8V
LTC1142-5 VIN = 8V
Figure 31B. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A,12V/0.15A) Measured Efficiency
Figure 31A. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter
+
+ +
1000pF
PDRIVE3
SENSE+3
SENSE –3
NDRIVE3
PGND3 SGND3 CT3 ITH3 ITH5 CT5 SGND5 PGND5
NDRIVE5
SENSE–5
SENSE+5
PDRIVE5
VIN3 SHUTDOWN 3 SHUTDOWN 5 VIN5
LTC1142HV
CT5 200pF
4 3 25 27 13 11 17 18
510Ω
3300pF 3300pFCT3 390pF
510Ω
1µF
224 16 10
9
15
14
20
23
1
28
6
VOUT5 5V/2A
C4 220µF
10V × 2
22µF 35V
RSENSE5 0.04Ω
1.8T 30µH
D2 MBRS140
Q3 Si9410DY
0V = NORMAL >1.5V = SHUTDOWN
1µF
C2 22µF 25V × 2
C1 22µF 25V × 2
VIN 6.5V TO 18V
Q4 Si9430DY
Q5 Si9410DY
D1 MBRS140
C3 100µF 10V × 2
L1 33µH
RSENSE3 0.05ΩVOUT3
3.3V/2A
AN54•F31A
+ +
Q2 Si9430DY
2000pF
C1, C2 C3, C4 L1 RSENSE3 RSENSE5 T1
AVX (Ta) TPS226K035R0300 AVX (Ta) TPSD227K010R0100 COILTRONICS CTX33-4 KRL SL-C1-1/2-0R050J KRL SL-C1-1/2-0R040J DALE LPE-6562-A026 PRIMARY: SECONDARY = 1:1.8
22Ω
R1 100Ω
T1
12V ENABLE 0V = 12V OFF >3V = 12V ON
(6V MAX)
1000pF
D3 MBRS140
R3 660k
R4 300k
20pF+
22µF 25V
12V/150mA
LT1121
VOUT
SHUTDOWN
VIN
ADJ
R2 100Ω
Q1 VN7002
R5 18k
+
GND
+
AN54-35
Application Note 54
LTC1148: High Efficiency Charger Circuit
The LTC1148 regulator can be used as a highly efficientbattery charging device. Figure 32 shows a circuit that isprogrammable for 1.3A fast charge or 100mA tricklecharge mode. During the fast charge interval, the resistordivider network (R4 and R5) forces the LTC1148 feedbackpin below 1.25V causing the regulator to operate at themaximum output current. Sense resistor R3 controls thecurrent at approximately 1.3A. When the batteries aredisconnected, the error amplifier sets the output voltage tobe 8.1V (for proper operation this voltage should exceed
maximum possible voltage across the battery pack). Di-ode D2 prevents the batteries from discharging throughthe divider network when the charger is shut down.
Dual rate charging is controlled by Q3 which selectsbetween fast and trickle charge. When the transistor turnson, R1 limits error amplifier output so that the currentlimiter starts operating at 100mA. If the trickle chargecurrent needs to be altered, adjust R1. With 1.3A outputcurrent, this charger is capable of efficiency in excess of90% which minimizes power dissipated in surface mountcomponents.
C1 (Ta) C3 AVX (Ta) TPSD226K025R0100 ESR = 0.100 I RMS = 0.775A C8 AVX (Ta) TPSE227M010R0100 ESR = 0.100I RMS = 1.149A Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W D1, D2 MOTOROLA SCHOTTKY VBR = 40V R3 KRL SP-1/2-A1-0R100J Pd = 0.75V L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE
ALL OTHER CAPACITORS ARE CERAMIC
VOUT = 1.25V • (1 + R4/R5) = 8.1V FAST CHARGE = 130mV/R3 = 1.3A TRICKLE CHARGE = 100mA EFFICIENCY > 90%
ITH
CT
LTC1148
VIN
SENSE +
SENSE –
+
C6 0.01µF
C7 100pF
+
VIN 8V TO 15V
C1 1µF
R2 1k
R1 51Ω
C4 3300pF X7R
C5 200pF NPO
10
0V = NORMAL > 1.5A = SHUTDOWN
4
1
8
7
9
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
D2 MBRS340T3
C3 22µF × 2 35V
R3 0.1Ω
R4 274k 1%
VOUT
C8 220µF 10V
3
11
12
Q3 VN2222LL
“1” TRICKLE CHARGE
SHUTDOWN
6
C2 0.1µF
+
L1 50µH1
2
4
3
AN54 • F32
SGND PGND
PDRIVE
VFB
NDRIVE
VBAT 4 CELLS
R5 49.9k 1%
Figure 32. LTC1148: High Efficiency Charger Circuit
Application Note 54
AN54-36
LTC1148: High Voltage Charger Circuit
Figure 33 is a variation of Figure 32. It is designed tocharge 6 cells and uses the LTC1148HV for higher inputvoltages. R4 value has been changed to provide 12.3Voutput when the battery is not connected.
C1 (Ta) C3 AVX (Ta) TPSD226K035R0200 ESR = 0.200 I RMS = 0.663A C8 AVX (Ta) TPSE107M016R0100 ESR = 0.100I RMS = 1.149A Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W D1, D2 MOTOROLA SCHOTTKY VBR = 40V R3 KRL SP-1/2-A1-0R100J Pd = 0.75V L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE
ALL OTHER CAPACITORS ARE CERAMIC
VOUT = 1.25V • (1 + R4/R5) = 12.3V FAST CHARGE = 120mV/R3 = 1.3A TRICKLE CHARGE = 100mA EFFICIENCY > 90%
ITH
CT
LTC1148HV
VIN
SENSE +
SENSE –
+
C6 0.01µF
C7 100pF
+
VIN 12V TO
18VC1 1µF
R2 1k
R1 51Ω
C4 3300pF X7R
C5 200pF NPO
10
0V = NORMAL > 1.5A = SHUTDOWN
4
1
8
7
9
14
Q1 Si9430DY
Q2 Si9410DY
D1 MBRS140T3
D2 MBRS340T3
C3 22µF × 2 35V
R3 0.1Ω
R4 442k 1%
VOUT
C8 100µF 16V × 2
3
11
12
Q3 VN2222LL
“1” TRICKLE CHARGE
SHUTDOWN
6
C2 0.1µF
+
L1 50µH1
2
4
3
AN54 • F33
SGND PGND
PDRIVE
VFB
NDRIVE
VBAT 6 CELLS
R5 49.9k 1%
Figure 33. LTC1148: High Voltage Charger Circuit
AN54-37
Application Note 54
LTC1142A: High Efficiency Power Supply Providing3.3V/2A with Built-In Battery Charger
Figure 34 implements a high efficiency step-down con-verter with a built-in battery charger using a single IC. Onesection of the dual LTC1142A is used to convert 4-cells to
3.3V/2A in a regular buck configuration. The other sectionis configured in the same way as the battery charger fromFigure 32. It is powered from a wall adapter and providesthe battery with fast or trickle charging rate. When theadapter is not connected, D3 prevents the battery fromdischarging through the R2/R1 divider network.
Figure 34. LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger
1000pF
+
++
1000pF
PDRIVE1
SENSE+1
SENSE–1
NDRIVE1
PGND1 SGND1 CT1 ITH1 ITH2 CT2 SGND2 PGND2
NDRIVE2
SENSE–2
VFB2VFB1
SENSE+2
PDRIVE2
VIN1 SHUTDOWN 1 SHUTDOWN 2 VIN2
LTC1142A
CT2 330pF
5 4 25 27 13 11 18 19
RC2 1k
RX 51Ω
CC1 3300pF
CC2 3300pF
CT1 200pF
RC1 1k
0.22µF
324 17
100pF 100pF
10
9
15
14
16
20
23
1
28
2
6
VOUT2 3.3V/2A
VBATT 4 CELLS NiCAD
COUT2 220µF 10V × 2
RSENSE2 0.05Ω
P-CH Si9433DY
L2 25µH
D2 MBRS140T3
N-CH Si9410DY
0.22µF
CIN2 22µF 25V × 2
CIN1 22µF 35V × 2 P-CH
Si9430DY
N-CH Si9410DY
D1 MBRS140T3
D3 MBRS340T3
COUT1 220µF
10V
L1 50µH
RSENSE1 0.1Ω
R2 274k
1%
R4 84.5k 1%
R3 51k 1%
R1 49.9k
1%
VIN 8V TO 18V
FROM WALL ADAPTER0V = CHARGE ON
>1.5V = CHARGE OFF0V = OUTPUT ON
>1.5V = 3.3V OUTPUT OFF
L1 L2 RSENSE1 RSENSE2
COILTRONICS CTX50-4 COILTRONICS CTX25-4 KRL SL-C1-1/2-1R100J KRL SL-C1-1/2-1R050J
FAST CHARGE = 130mV/RSENSE1 = 1.3A TRICKLE CHARGE = 130mV/RSENSE1 = 100mA AN54 • F34
+
“1” FOR TRICKLE CHARGE
VN2222LL
Application Note 54
AN54-38
LTC1149: Dual Output Buck Converter
The circuit shown in Figure 35A implements the mostelegant approach for dual output regulators that provide3.3V and 5V outputs. It uses a single LTC1149. Thesynchronous rectification feature of this chip is used toprovide excellent efficiency, as well as good cross regula-tion between the two outputs. Maximum output power ofthe converter is 17W, which may be drawn in any combi-nation between 3.3V and 5V outputs.
A regular buck regulator is used for producing 3.3V outputwith T1’s primary in place of the buck inductor. Thesecondary of T1 forms a boost winding for 5V output. Thetransformer is wound with a simple trifilar winding toensure that the primary is closely coupled to the second-ary. Superior cross regulation is achieved by the closeprimary-to-secondary coupling and by splitting voltagefeedback paths (resistors R1 and R2 provide feedbacksignals from both 3.3V and 5V outputs). Diodes D1, D2and capacitor C7 comprise a soft-start circuit that causesthe output voltage to increase slowly when the power isfirst applied to the circuit. This circuit prevents overshoot
at the 3.3V output. The transformer used in this exampleis a standard product (see the parts list). A circuit boardhas been laid out for this circuit and has subsequentlybeen thoroughly tested under full operating conditionsand optimized for mass production requirements. A Ger-ber file for the board is available upon request.
Figure 35A. Single LTC1149: Dual Output Buck Converter
VINS/D1/VFB
S/D2
CT
ITH
VO(REG)
VI(REG)
CAP
PGATE
PDRIVE
NGATE
SENSE+
SENSE–
RGNDPGND SGND
LTC1149
10
15
6
7
3
5
16
C12 56pF
C13 2.2µF
12 14 11
1
4
13
9
8
R5 24.9k 1%
R4 1k
C8 0.068µF
C3, C4, C15, C16 C5, C6, C8, C17 R3 T1
AVX (Ta) TPSE227M010R 49BCPA AVX (Ta) TPSE226M035R 49BCPA IRC LR512-01-R020F HURRICANE, HL-8700
C10 2200pF
C11 1000pF
2
C19 0.1µF
D3 BAS16
C9 0.047µF
C14 1000pF
D1 BAS16
C7 10µF
QP1 Si9435DY
R6 100Ω
R7 100Ω
C20 1µF
4 QP2 Si9435DY
+
1
43
6
TP1
•
••
5
2
T1 HL-8700
–VIN
VIN 6V TO
24V +C5 22µF
+C6 22µF
+C17 22µF
+C18 22µF
R1 102k 1%
4
R8 33k
D6 BAS16
QN1 Si9410DY
D4 MBRS140
QN2 Si9410DY
+C1 220µF +C2
220µF
+C15 220µF +C16
220µF
+C3 220µF
D2 BAS16
R2 124k 1%
+C4 220µF
– VOUT
3.3V OUT
5V OUT
BOLD LINES INDICATE HIGH CURRENT PATHS (SHORT LEADS)
R3 0.02Ω
D5 MBRS140
AN54 • F35A
11 T11 T
11 T
Figure 35B. LTC1149: Dual Output Buck ConverterMeasured Efficiency
TOTAL POWER OUTPUT0
80
EFFI
CIEN
CY (%
)
82
86
88
90
100
94
4 8 10 18
AN54 • F35B
84
96
98
92
2 6 12 14 16
VIN = 6V
VIN = 20V
VIN = 12V
AN54-39
Application Note 54
LTC1148: Constant Frequency Buck Converters
Finally, Figures 36A and 37A show circuits that completelysatisfy the demand in ultra-high efficiency convertersoperating synchronously with an external clock. The risingedge of the clock saturates Q3 pulling pin 4 below theinternal comparator threshold. The internal logic assumesthe end of the off-time, and turns Q1 on. Now the LTC1148operates as a conventional constant frequency currentmode controller and therefore requires slope compensa-tion. Q2 generates an artificial ramp signal that is superim-posed on the inductor current waveform sensed by theshunt R7. This is a standard technique to eliminatesubharmonic oscillation, a phenomenon that occurs un-der simultaneous conditions of fixed frequency and fixedamplitude of inductor current when the duty cycle exceeds50%. Subharmonic oscillations are not related to theclosed-loop transfer function.
Figure 36B. LTC1148: (8V-15V to 5V/2A)Constant Frequency Buck ConverterMeasured Efficiency
OUTPUT CURRENT (A)0.1
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
651 10
AN54 • F36B
VIN = 8V
VIN = 15V
AN54 • F36A
C8 1000pF
SLOPE COMPENSATION
Q1 Si9430DY
Q4 Si9410DY
C7 22µF 25V × 2
C9 220µF 10VC6
200pFC5
6800pF
10
6
4
11
1
8
7
14
12
3
U1
D3 MBR130T3
D2 1N4148
C7 AVX (Ta) TPSD226K025R0200 C9 AVX (Ta) TPSE227K010R0080 L1 COILTRONICS CTX15-4 R7 KRL SL-1-C1-0R040J PD = 1W
OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL. FOR APPLICATIONS WITH VIN > 2VOUT SLOPE COMPENSATION CAN BE DELETED.
+
Q2 2N2222
D1 1N4148
D4 1N4148
LTC1148-5
VIN
SHUTDOWN
ITH
CT
SGND
PDRIVE
SENSE+
SENSE–
NDRIVE
PGND
L1 15µH
R3 220Ω
R5 750Ω
R8 100Ω
R7 0.04Ω
R9 100Ω
R4 100Ω
C4 51pF
Q3 2N2222
R10 510k
+
+
C2 0.1µF
C3 1µF
C1 100pF
R6 1k
R1 30k
> 1.5V = SHUTDOWN
OSC IN 200kHz R2
5.1k
VOUT 5V 2A
VIN 8V TO 15V
Figure 36A. LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter
Application Note 54
AN54-40
If the input voltage always exceeds twice the output (dutycycle in this case would be less than 50%) the circuit insidethe dashed box can be omitted. Resistor R11 is added tothe circuit of disable Burst Mode operation ensuring truein-sync operation over the full range of output current. Thecircuitry is designed to be synchronized by a 200kHzclock to accommodate other external frequencies; nothingmore than component value changes is required. If theinput voltage goes beyond specified range, the controllerwill lose synchronization (it will still regulate, however).R10 increases input voltage pull-in range and can beomitted if it is not required. Values above 430k ensureproper start-up.
OUTPUT CURRENT (A)0.1
EFFI
CIEN
CY (%
)
100
95
90
85
80
75
70
651 10
AN54 • F37B
4.5V TO 3.3V/2A
6.5V TO 3.3V/2A
Figure 37B. LTC1148: (4.5V-6.5V to 3.3V/2A)Constant Frequency Buck ConverterMeasured Efficiency
Figure 37A. LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter
AN54 • F37A
C8 1000pF
SLOPE COMPENSATION
Q1 Si9430DY
Q4 Si9410DY
C7 22µF 25V × 2
C9 220µF 10VC6
150pFC5
3300pF
10
6
4
11
1
8
7
14
12
3
U1
D3 MBR130T3
D2 1N4148
C7 AVX (Ta) TPSD226K025R0200 C9 AVX (Ta) TPSE227K010R0080 L1 COILTRONICS CTX15-4 R7 KRL SL-1-C1-R040J PD = 1W
OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL.
+
Q2 2N2222
D1 1N4148
D4 1N4148
LTC1148-3.3
VIN
SHUTDOWN
ITH
CT
SGND
PDRIVE
SENSE+
SENSE–
NDRIVE
PGND
L1 15µH
R5 750Ω
R8 100Ω
R7 0.04Ω
R9 100Ω
R4 100Ω
C4 50pF
Q3 2N2222
R10 470k
+
+
C2 0.1µF
C3 1µF
C1 100pF
R6 100Ω
R1 20k
> 1.5V = SHUTDOWN
OSC IN 200kHz R2
2.2k
VOUT 3.3V 2A
VIN 4.5V TO 6.5V
R11 18k
AN54-41
Application Note 54
APPENDIX A
TOPICS OF COMMON INTEREST
Defeating Bust Mode Operation
Sometimes applications require Burst Mode operation tobe defeated. It might be useful in a high output currentcircuit which never operates at light loads. Ensuringcontinuous operation in this case usually improves thecircuit noise immunity and helps to eliminate audible noisefrom certain types of inductors when they are lighterloaded. The Burst Mode operation should be disabled if anoverwinding is used to provide boosted voltage, additionalto the main output (for example, see Figure 30A). Thisallows to draw power from the secondary with improvedcross-regulation, even if the primary output is not loaded.Defeating of Burst Mode operation should also be consid-ered when the fixed frequency circuits from Figures 36Aand 37A are used. With continuous operation these cir-cuits always operate fully synchronized to the externalclock.
Whatever the reason, Burst Mode operation can be sup-pressed with a simple external network which cancels the25mV minimum current comparator threshold. An exter-nal offset is put in series with the SENSE – pin to subtractfrom the built-in 25mV offset. An example of this tech-nique is shown in Figure A1.
LTC1148 FAMILY R2
100Ω
L 33µH
R1 100ΩR3
20k
SENSE+
100pF
SENSE–
RSENSE 0.05Ω VOUT
5V 2A
AN54 • FA01
Two 100Ω resistors are inserted in series with the leadsfrom the sense resistor. With the addition of R3, a currentis generated through R1 causing an offset of:
V VR
R ROFFSET OUT= ×+
11 3
If VOFFSET exceeds 25mV the minimum threshold will becancelled and Burst Mode operation is prevented fromoccurring. Since the offset voltage is constant, the maxi-mum load current is also decreased. Thus to get back tothe same output current, the sense resistor must be lower:
RmV
ISENSEMAX
= 75
Soft-Start Circuits
Right after the power-on, the regulator operates in a short-circuit condition while charging output capacitors. Withearlier voltage mode converters, this led to enormouscurrent transient at start-up. Soft-start circuits were usu-ally added to fix this problem. The LTC1148 seriesimplements current mode technique which inherentlyprovides current limiting and does not require any specialsoft-start circuits. Start-up current is limited to the short-circuit current value of 150mV/RSENSE.
Some applications might, however, require softer start. Ithelps to avoid output overshoot when the power is firstapplied to the circuit, and it also prevents the inputsupply’s overcurrent protection from latching, when theinput voltage increases slowly. Figures A2 and A3 providepossible solutions for soft-start. Capacitor C1 in Figure A2holds down ITH pin limiting the output current. C1 ischarged via R1, when the voltage across its terminalsexceeds DC level of ITH pin, D2 becomes reverse-biasedand the capacitor no longer has an effect on the circuitoperation. D1 provides discharge path for C1 when theinput voltage is removed. The soft-start time constant isdefined by R1 and C1.
In Figure A3, capacitor C1 holds down the SENSE– pinproviding additional offset to the current comparator. C1charges through D1 and R2, slowly increasing maximumoperating current. When C1 is fully charged D1 is reverse-biased and the capacitor no longer affects the operation.
Figure A1. Defeating Burst Mode
Application Note 54
AN54-42
D2 provides a discharge path for C1 when the outputvoltage disappears. The soft-start time constant is definedby R2 and C1.
LTC1148 FAMILY
R2 1k
D2 MBR0520L
VIN
ITH
C2 3300pF
C1 4.7µF
16V
VIN
AN54 • FA02
R1 22k
D1 1N4148
+
Figure A2. Soft-Start Circuit with ITH Pin Clamping
Figure A3. Soft-Start Circuit with Sense Pin Clamping
LTC1148 FAMILY R1
100Ω
L 33µH
R2 100Ω
SENSE+
C2 1000pF
D1 1N4148
D2 1N4148
C1 10µF 10V
SENSE–
RSENSE 0.05Ω VOUT
5V 2A
AN54 • FA03
+
Frequency Compensation
The LTC1148 family of regulators contains both voltageand current loops, which, together with external capaci-tors and inductors, require a pretty complex mathematicalapproach to frequency compensation. Operating pointchanges with input voltage and output current variationsadd complications and suggest a more practical empiricalmethod.
The simplest approach uses load step transient by switch-ing in an additional load resistor and simultaneouslymonitoring the output. Switching regulators take severalcycles to respond to a step in resistive load current. Whena load step occurs, output voltage shifts by an amountequal to ∆ILOAD × ESR, where ESR is the output capacitoreffective series resistance. Load current change also be-gins to charge or discharge output capacitor until theregulator loop adapts to the current change and returnsVOUT to its steady state value. If during this recovery timeVOUT has ringing, it indicates a stability problem, and thecapacitor at ITH pin should be increased.
A simple dynamic load circuit is shown in Figure A4 wherethe MOSFET Q1, driven by an external generator, switchesa load resistor R2 in and out. The generator should provide10V gate drive (not a TTL level). The drive signal frequencyis not critical. A good starting point is 500Hz and the loadchange from 50% to the full load.
Figure A4. Simple Dynamic Load
The LTC1148 series regulators provide a very stableoperation. The compensation values used in the circuits inthis note have been tested over the wide range of operatingconditions and proved to provide an adequate compensa-tion for most applications. Usually no stability testing, asdescribed above, is required.
LTC1148 FAMILY
GENERATOR IN (10VP-P)
Q1 IRFZ44
(HEAD SINK MAY BE REQUIRED)
R1 R2COUT
AN54 • FA04
100k
+
AN54-43
Application Note 54
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
APPENDIX B
SUGGESTED MANUFACTURERS
Linear Technology provides this list of manufacturers toget you started in your component selection process. Wemake no claims about any of these companies except thatthey provide components necessary in switching powersupplies. There are many more companies to choosefrom; for a more complete list refer to the PCIM Buyer’s
Guide. PCIM (Power Conversion & Intelligent Motion) ispublished by Intertec International Inc., 2472 EastmanAve., Bldg. 33-34, Ventura, California 93003-5774, (805)650-7070. PCIM is free to qualified applicants. Backissues, such as the Buyer’s Guide can be purchased.
Philips Components1440 W. Indian Town Rd.Jupiter, FL 33458(407) 744-4200Cer., Chip Capacitors
Murata Erie North America1900 W. College Ave.State College, PA 16801(814) 237-1431
Nichicon (America) Corporation927 East State ParkwaySchaumburg, IL 60173(708) 843-7500Aluminum Electrolytic
Sanyo Video Components (USA) Corp.2001 Sanyo Ave.San Diego, CA 92173(619) 661-6835Low ESR Filter Capacitors-Solid AluminumElectrolytic Capacitors (OS-CON)
Sprague678 Main St.P.O. Box 231Sanford, ME 04073(207) 324-4140Tantalum Capacitors
Current Sense ResistorsDale Electronics1122 23rd St.P.O.Box 609Columbus, NE 68602(402) 564-3131Resistors, Inductors, Xformers
IRC4222 South Staples St.Corpus Christi, TX 78411(512) 992-7900
KRL160 Bouchard St.Manchester, NH 03103(603) 668-3210
DiodesFuji/Collmer14368 Proton Rd.Dallas, TX 75244(214) 233-1589Low Current Schottkys
General Instruments10 Melville Park Rd.Melville, NY 11747(516) 847-3222
Motorola Inc.5005 E. McDowell Rd.P.O. Box 2953Phoenix, AZ 85062(602) 244-5768Diodes
Philips Components Disc. Prod. Div.100 Providence PikeSlatersville, RI 02876(401) 762-3800Discrete Semi Group
Ferrite BeadsFair-Rite Products Corp.1 Commerial RowP.O. Box JWallkill, NY 12589(914) 895-2055
Toshiba America Elec. Components9775 Toledo WayIrvine, CA 92718(714) 455-2000
Heat SinksAavid Engineering, Inc.One Kool Path Box 400Laconia, NH 03247(603) 528-3400
Int’l Electronic Research Group135 W. Magnolia Blvd.Burbank, CA 91502(213) 849-2481
BatteriesDuracellOEM Sales & MarketingBerkshire Industrial ParkBethel, CT 06801(800) 431-2656
Eveready Battery Co.Checkerboard SquareSt. Louis, MO 63164(314) 982-2000
Bipolar TransistorsMotorola Inc.3102 North 56th St.MS 56-126Phoenix, AZ 85018(800) 521-6274Full Line
Zetex87 Modular Ave.Commack, NY 11725(516) 543-7100High Gain Bipolar Switching Transistorsincluding Surface Mount Devices
CapacitorsAVX CorporationP.O. Box 867Myrtle Beach, SC 29578(803) 946-0690Tant., Cer., Surface Mount
Elpac1567 Reynolds Ave.Irvine, CA 92714Film Capacitors(714) 476-6070Film Capacitors
Intertechnical Group2269 Saw Mill River Rd., Bldg. 4CP.O. Box 217Elmsford, NY 10523(914) 347-2474Polycarbonate Film
Application Note 54
AN54-44 LINEAR TECHNOLOGY CORPORATION 1993
LT/GP 1094 5K REV A • PRINTED IN USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7487(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
Thermalloy2021 W. Valley View LaneDallas, TX 75234(214) 243-4321
Inductors and TransformersBeckman Industrial Corp.4200 Bonita PlaceFullerton, CA 92635(714) 447-2345Inductors, Xformers including SMT
Caddell-Burns258 East Second St.Mineola, NY 11501(516) 746-2310
Coilcraft1102 Silver Lake Rd.Cary, IL 60013(800) 322-2645
Coiltronics6000 Park of Commerce Blvd.Boca Raton, FL 33487(407) 241-7876Full Line including Surface Mount Inductors
Dale ElectronicsE. Highway 50P. O. Box 180Yankton, SD 57078(605) 665-9301Inductors, Xformers including SMT
Gowanda Electronics Corp.1 Industrial PlaceGowanda, NY 14070(716) 532-2234
Hurricane Electronics LabP.O. Box 1280Hurricane, UT 84737(801) 635-2003
Murata Erie North America2200 Lake Park DriveSmyrna, GA 30080(404) 436-1300
Renco60 E. Jefryn Blvd.Deerpark, NY 11729(516) 586-5566
Sumida Electronic5999 New Wilke Rd., Ste. 110Rolling Meadows, IL 60008(708) 956-0666
TDK Corp. of America1600 Feehanville Dr.Mount Prospect, IL 60056(708) 803-6100
Thermalloy2021 W. Valley View LaneDallas, TX 75234(214) 243-4321Power Sockets, Thermal Compounds,and Adhesives Thermally ConductiveInsulators, Mounting Kits
Power MOSFETsInternational Rectifier Corp.233 Kansas St.El Segundo, CA 90245(310) 322-3331
Motorola Inc.5005 E. McDowell Rd.Phoenix, AZ 85008(602) 244-3576
Siliconix2201 Laurelwood Rd.Santa Clara, CA 96056(800) 554-5565
ResistorsMicro-Ohm Corp.1088 Hamilton Rd.Duarte, CA 91010(818) 357-5377
Thermo Disc1981 Port City Blvd.Muskegon, MI 49443(616) 777-2602
RCD Components, Inc.520 East Industrial Park Dr.Manchester, NH 03109(603) 669-0054
Caddock Electronics1717 Chicago Ave.Riverside, CA 92507-2364(909) 788-1700
WireBelden Wire & CableP.O. BOX 1980Richmond, IN 47375(317) 983-5200
Toko America Incorporated1250 Feehanville Dr.Mount Propsect, IL 60056(708) 635-3200
Magnetic MaterialsFair-Rite Products Corp.1 Commercial RowP. O. Box JWallkill, NY 12589(914) 895-2055Ferrite
Micrometals, Inc.1190 N. Hawk CircleAnaheim, CA 92807(800) 356-5977Powdered Iron
Magnetics Div. Spang & CoP.O. Box 391Butler, PA 16003-0391(412) 282-8282Molypermalloy, Kool Mµ, Ferrite
Philips Components Disc. Prod. Div.Materials Group1033 King HighwaySaugerties, NY 12477(914) 246-2811Ferrite
Pyroferric International, Inc.200 Madison St.Toledo, IL 62468(217) 849-3300Powdered Iron
Siemens Components, Inc.186 Wood Ave. SouthIselin, NJ 08830(908) 906-4300Ferrite
TDK Corp. of America1600 Feehanville Dr.Mount Prospect, IL 60056(708) 803-6100Ferrite
Mounting HardwareBergquist5300 Edina Industrial Blvd.Minneapolis, MN 55439(612) 835-2322Thermally Conductive Insulators
Stockwell Rubber4749 Tolbut St.Philadelphia, PA 19136(800) 523-0123Thermally Conductive Insulators