data sheet ic fr9886

8/13/2019 Data Sheet ic fr9886

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2FR9886- 1.0-APR-2011

FR9886

Tfitipower integrated technology lnc.

Typical Application Circuit

FR9886

SSGND

NC

VIN

BOOST

FB

LXVIN4.5V to 23V

VOUT

10uF/25V

CERAMIC x 2 22uF/6.3V

CERAMIC x 2

L1

4.7uH~15uH

C3

10nF ~ 0.1uF

R2

R1

R3

10k~100k

1

2 3

4

56

7

8

C6(optional)

C1C2

C4 10nF~0.1uF

SHDN

3.3V

10k

26.1k

Figure 2. CIN /COUTuse Ceramic Capacitors Application Circuit

FR9886

SSGND

NC

VIN

BOOST

FB

LXVIN

4.5V to 23V

VOUT

0.1uF/25V

CERAMIC x 1

100uF/6.3V

EC x 1

R2

R1

1

2 3

4

56

7

8

C6(optional)C1 C2100uF/25V

EC x 1

C5

L1

4.7uH~15uH

C4

10nF~0.1uFR3

10k~100k

C3

10nF ~ 0.1uF

SHDN

3.3V

26.1k

10k

Figure 3. CIN /COUTuse Electrolytic Capacitors Application Circuit

VOUT R1 R2 C6 L1 COUT1.2V 3k 10k 200pF~1nF 4.7uH 22uF MLCC x2

1.8V 9.53k 10k 200pF~1nF 4.7uH 22uF MLCC x2

2.5V 16.9k 10k 200pF~1nF 10uH 22uF MLCC x2

3.3V 26.1k 10k 200pF~1nF 10uH 22uF MLCC x2

5V 44.2k 10k 200pF~1nF 10uH 22uF MLCC x2

1.2V 3k 10k -- 4.7uH 100uF EC x1

1.8V 9.53k 10k -- 4.7 H 100uF EC x1

2.5V 16.9k 10k -- 10uH 100uF EC x1

3.3V 26.1k 10k -- 10uH 100uF EC x1

5V 44.2k 10k -- 10uH 100uF EC x1

Table 1. Recommended Component Values


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FR9886


Functional Pin Description

I/O Pin Name Pin No. Pin Function

I FB 5Voltage Feedback Input Pin. Connect FB and VOUTwith a resistive voltagedivider. This IC senses feedback voltage via FB and regulates it at 0.925V.

I VIN 2Power Supply Input Pin. Drive this pin by 4.5V to 23V voltage to power on thechip.

I SHDN 7Enable Input Pin. This pin provides a digital control to turn the converter on oroff. Connect VIN with a 100K resistor for self-startup.

I GND 4 Ground Pin. Connect this pin to exposed pad.

O LX 3Power Switching Output. It is the output pin of internal high side NMOS whichis the switching to supply power.

O SS 8Soft-Start Pin. This pin controls the soft-start period. Connect a capacitor

from SS to GND to set the soft start period.

O BOOST 1High Side Gate Drive Boost Pin. A 10nF or greater capacitor must beconnected from this pin to LX. It can boost the gate drive to fully turn on theinternal high side NMOS.

O NC 6 No connection. Keeps this pin floating.

Block Diagram

PWM

Control

Driver

Logic

BOOST

LXR

OTP

OVP

UVLO

Current

Comp

S

Oscillator

High-Side

MOSFET

Low-Side

MOSFET

ISEN

SS

FB

0.925V

UVLO

&

POR

VIN

VCC

GND

Current

Limit

OTPInternal

RegulatorVCC

OVP

6A

1M

SHDN

Figure 4. Block Diagram of FR9886


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FR9886


Absolute Maximum Ratings(Note1)

Supply Voltage V IN-------------------------------------------------------------------------------------- -0.3V to +25V

Enable Voltage V SHDN --------------------------------------------------------------------------------- -0.3V to +25V

LX Voltage V LX (50ns)---------------------------------------------------------------------------------- -1V to VIN+0.3V

Boost Trap Voltage V BOOST---------------------------------------------------------------------------- VLX-0.3V to VLX+6V

All Other Pins Voltage---------------------------------------------------------------------------------- -0.3V to +6V

Maximum Junction Temperature (T J)-------------------------------------------------------------- +150

Storage Temperature (T S)----------------------------------------------------------------------------- -65 to +150

Lead Temperature (Soldering, 10sec.) ----------------------------------------------------------- +260C

Power Dissipation @TA=25 , (PD) (Note2)

SOP-8 ----------------------------------------------------------------------------------------- 1.39 W

SOP-8 (Exposed Pad )-------------------------------------------------------------------- 2.08 W

Package Thermal Resistance, ( JA):

SOP-8------------------------------------------------------------------------------------------ 90C/W

SOP-8 (Exposed Pad )-------------------------------------------------------------------- 60C/W

Package Thermal Resistance, ( JC):

SOP-8------------------------------------------------------------------------------------------ 39C/W

SOP-8 (Exposed Pad )-------------------------------------------------------------------- 15C/W

Note1Stresses beyond this listed under Absolute Maximum Ratings" may cause permanent damage to the device.

Note2PCB heat sink copper area = 10mm2.

Recommended Operating Conditions

Supply Voltage V IN------------------------------------------------------------------------------------ +4.5V to +23V

Enable Voltage V SHDN ------------------------------------------------------------------------------- 0V to VIN

Operation Temperature Range--------------------------------------------------------------------- - 40C to + 85C


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FR9886


Electrical Characteristics

(VIN=12V, TA=25 , unless otherwise specified.)

Parameter Symbol Conditions Min Typ Max Unit

VINInput Supply Voltage VIN 4.5 23 V

VINQuiescent Current I DDQ V HDN=1.8V, VFB=1.0V 2.5 mA

VIN Shutdown Supply Current ISD V HDN=0V 1 A

Feedback Voltage VFB 4.5VVIN23V 0.9 0.925 0.95 V

Feedback OVP Threshold Voltage VOVP 1.5 V

High-Side MOSFET RDS(ON) (Note3) RDS(ON) 120 m

Low-Side MOSFET RDS(ON) (Note3) RDS(ON) 100 m

High-Side MOSFET Leakage Current ILX(leak) V HDN=0V, VLX=0V 10 uA

High-Side MOSFET Current Limit (Note3) ILIMIT(HS) Minimum Duty 3.5 4.5 A

Low-Side MOSFET Current Limit (Note3) ILIMIT(LS) From Drain to Source 1.5 A

Error Amplifier Voltage Gain (Note3) 400 V/V

Oscillation frequency FOSC 290 340 420 KHz

Short Circuit Oscillation Frequency FOSC(short) V FB=0V 110 KHz

Maximum Duty Cycle DMAX V FB=0.8V 90 %

Minimum On Time (Note3) TMIN 100 ns

Input UVLO Threshold VUVLO(Vth) V INRising 4.3 V

Under Voltage Lockout ThresholdHysteresis

VUVLO(HYS) 250 mV

Soft-Start Current ISS V SS=0V 6 uA

Soft-Start Period TSS C SS=0.1uF 15 ms

SHDN Input Low Voltage VSHDN (L) 0.4 VSHDN Input High Voltage VSHDN (H) 2 V

SHDN Input Current ISHDN V HDN=2V 2 uAThermal Shutdown Threshold (Note3) TSD 170

Note3Not production tested.


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Typical Performance Curves

VIN = 12V, VOUT= 3.3V, C1 =10uF x 2, C2 = 22uF x 2, L1 = 10uH, TA = +25, unless otherwise noted.

Figure 5. Efficiency vs. Load Current Figure 6. Efficiency vs. Load Current

Figure 7. Efficiency vs. Load Current Figure 8. Current Limit vs. Temperature

Figure 9. Feedback Voltage vs.Temperature Figure 10. Switching Frequency vs. Temperature

VOUT = 1.2V VOUT = 3.3V

VOUT = 5V


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VIN= 12V, V OUT= 3.3V, C1 = 10uF x 2, C2 = 22uF x 2, L1 = 10uH, TA = +25 , unless otherwise noted.

IOUT=0A IOUT=2.5A

Figure 11. Steady State Waveform Figure 12. Steady State Waveform

IOUT=0A IOUT=2.5A

Figure 13. Power On through VIN Waveform Figure 14. Power On through VIN Waveform

IOUT=0A IOUT=2.5A

Figure 15. Power Off through VIN Waveform Figure 16. Power Off through VIN Waveform

VIN 10mV/div. (AC)

VOUT 20mV/div. (AC)

IL1A/div.

VLX5V/div.

2us/div.

VIN 5V/div.

IL1A/div.

VLX5V/div.

20ms/div.

VIN 5V/div.

VOUT 1V/div.

IL1A/div.

VLX5V/div.

20ms/div.

VOUT 1V/div.

20ms/div. 20ms/div.

2us/div.

VIN 100mV/div. (AC)

VOUT 20mV/div. (AC)

IL1A/div.

VLX5V/div.

VIN 10V/div.

VOUT 1V/div.

IL1A/div.

VLX5V/div.

VIN 10V/div.

VOUT 1V/div.

IL1A/div.

VLX5V/div.


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VIN= 12V, V OUT= 3.3V, C1 = 10uF x 2, C2 = 22uF x 2, L1 = 10uH, TA = +25 , unless otherwise noted.

IOUT=0A IOUT=2.5A

Figure 17. Power On through SHDN Waveform Figure 18. Power On through SHDN WaveformIOUT=0A

IOUT=2.5A

Figure 19. Power Off through SHDN Waveform Figure 20. Power Off through SHDN Waveform

Figure 21. Load Transient Waveform Figure 22. Short Circuit Test

VSHDN 5V/div.

VOUT 1V/div.

IL1A/div.

VLX5V/div.

4ms/div.

VSHDN 5V/div.

IL1A/div.

VLX5V/div.

4ms/div.

VSHDN 5V/div.

VOUT 1V/div.

IL1A/div.

VLX5V/div.

80us/div.

VOUT 1V/div.

400us/div. 40us/div.

4ms/div.

VOUT 200mV/div.

IL1A/div.

VOUT 1V/div.

IL1A/div.

VSHDN 5V/div.

VOUT 1V/div.

IL1A/div.

VLX5V/div.


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Function Description

The FR9886 is a high efficiency, internalcompensation, and constant frequency current modestep-down synchronous DC/DC converter. It hasintegrated high-side (120m, typ) and low-side(100m, typ) power switches, and provides 2.5Acontinuous load current. It regulates input voltagefrom 4.5V to 23V, and down to an output voltage aslow as 0.925V.

Control Loop

Under normal operation, the output voltage is sensedby FB pin through a resistive voltage divider andamplified through the error amplifier. The voltage of

error amplifier output is compared to the switchcurrent to control the RS latch. At the beginning ofeach clock cycle, the high-side NMOS turns on whenthe oscillator sets the RS latch, and turns off whencurrent comparator resets the RS latch. Then thelow-side NMOS turns on until the clock period ends.

Enable

The FR9886 SHDN pin provides digital control toturn on/turn off the regulator. When the voltage of

SHDN exceeds the threshold voltage, the regulator

starts the soft start function. If the SHDN pinvoltage is below than the shutdown threshold voltage,the regulator will turn into the shutdown mode andthe shutdown current will be smaller than 1uA. Forauto start-up operation, connect EN to VIN through a100Kresistor.

Soft Start

The FR9886 employs adjustable soft start function toreduce input inrush current during start up. Whenthe device turns on, a 6uA current begins chargingthe capacitor which is connected from SS pin toGND. The equation for the soft start time is shownas below:

SS FB

SS

SS

C nF VT ms =

I uA

The VFBvoltage is 0.925V and the I SScurrent is 6uA.If a 0.1uF capacitor is connected from SS pin toGND, the soft start time will be 15ms.

Output Over Voltage Protection

When the FB pin voltage exceeds 1.5V, the outputover voltage protection function will be triggered andturn off the high-side/low-side MOSFET.

Input Under Voltage LockoutWhen the FR9886 is power on, the internalcircuits are held inactive until VIN voltageexceeds the input UVLO threshold voltage.And the regulator will be disabled when VIN is below the input UVLO threshold voltage. Thehysteretic of the UVLO comparator is 250mV(typ).

Short Circuit Protection

The FR9886 provides short circuit protectionfunction to prevent the device damage fromshort condition. When the short conditionoccurs and the feedback voltage drops lowerthan 0.4V, the oscillator frequency will bereduced to 110KHz to prevent the inductorcurrent increasing beyond the current limit. Inthe meantime, the current limit will also bereduced to lower the short current. Once theshort condition is removed, the frequency andcurrent limit will return to normal.

Over Current Protection

The FR9886 over current protection function isimplemented using cycle-by-cycle current limit

architecture. The inductor current ismonitored by measuring the high-sideMOSFET series sense resistor voltage. Whenthe load current increases, the inductor currentalso increases. When the peak inductor currentreaches the current limit threshold, the outputvoltage starts to drop. When the over currentcondition is removed, the output voltage returnsto the regulated value.

Over Temperature Protection

The FR9886 incorporates an over temperatureprotection circuit to protect itself from

overheating. When the junction temperatureexceeds the thermal shutdown thresholdtemperature, the regulator will be shutdown.And the hysteretic of the over temperatureprotection is 60(typ).

Internal Compensation Function

The stability of the feedback circuit is controlledthrough internal compensation circuits. Thisinternal compensation function is optimized formost applications and this function can reduceexternal R, C components.


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Application Information

Output Voltage Setting

The output voltage VOUT is set using a resistivedivider from the output to FB. The FB pin regulatedvoltage is 0.925V. Thus the output voltage is:

OUTR1

V =0.925V 1+R2

Table 2 lists recommended values of R1 and R2 formost used output voltage.

Table 2 Recommended Resistance Values

VOUT

R1 R2

5V 44.2k 10k

3.3V 26.1k 10k

2.5V 16.9k 10k

1.8V 9.53k 10k

1.2V 3k 10k

Place resistors R1 and R2 close to FB pin to preventstray pickup.

Input Capacitor Selection

The use of the input capacitor is filtering the inputvoltage ripple and the MOSFETS switching spikevoltage. Because the input current to the step-downconverter is discontinuous, the input capacitor isrequired to supply the current to the converter tokeep the DC input voltage. The capacitor voltagerating should be 1.25 to 1.5 times greater than themaximum input voltage. The input capacitor ripplecurrent RMS value is calculated as:

IN RMS OUTI =I D 1-D

Where D is the duty cycle of the power MOSFET.

This function reaches the maximum value at D=0.5and the equivalent RMS current is equal to IOUT/2.The following diagram is the graphical representationof above equation.

A low ESR capacitor is required to keep thenoise minimum. Ceramic capacitors arebetter, but tantalum or low ESR electrolyticcapacitors may also suffice. When usingtantalum or electrolytic capacitors, a 0.1uFceramic capacitor should be placed as close tothe IC as possible.

Output Capacitor Selection

The output capacitor is used to keep the DCoutput voltage and supply the load transientcurrent. When operating in constant current

mode, the output ripple is determined by fourcomponents:

RIPPLE RIPPLE(C) RIPPLE(ESR)

RIPPLE(ESL) NOISE

V t V t V t

V t V

The following figures show the form of the ripplecontributions.

VRIPPLE(ESR)(t)

+

VRIPPLE(ESL)(t)

+

VRIPPLE(C)(t)

+

VNOISE

=

VRIPPLE(t)

1A

1.5A

2A

2.5A

(t)

(t)

(t)

(t)


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RIPPLE(ESR) L (ESR)V = I R

RIPPLE(ESL) L (ESL) OSC

1V = I L F

D 1

D

RIPPLE(C) L

OUT OSC

1V = I

8 C F

OUT OUTL

OSC IN

V VI 1

F L V

Where IL is the peak-to-peak inductor ripple

current, FOSC is the switching frequency, L is the

inductance value, VINis the input voltage, V OUTis theoutput voltage, R(ESR) is the equivalent seriesresistance value of the output capacitor, L(ESL) is theequivalent series inductance value of the outputcapacitor and the COUT is the output capacitor. Thefollowing diagram is an example to graphicalrepresent IL equation.

Low ESR capacitors are preferred. Ceramic,tantalum or low ESR electrolytic capacitors can beused depending on the output ripple requirement.When using the ceramic capacitors, the ESL

component is usually negligible.It is important to use the proper method to eliminatehigh frequency noise when measuring the outputripple. The figure shows how to locate the probeacross the capacitor when measuring output ripple.Removing the scope probe plastic jacket in order toexpose the ground at the tip of the probe. It gives avery short connection from the probe ground to thecapacitor and eliminating noise.

Output Inductor Selection

The output inductor is used for storing energyand filtering output ripple current. But thetrade-off condition often happens betweenmaximum energy storage and the physical sizeof the inductor. The first consideration forselecting the output inductor is to make surethat the inductance is large enough to keep theconverter in the continuous current mode.That will lower ripple current and result in loweroutput ripple voltage. The inductance valueshould be determined to set the peak-to-peakinductor ripple current ILaround 20% to 50%

of the maximum load current. Then theinductance can be calculated with the followingequation:

L OUT(MAX)I = 0.2~0.5 I

OUT

IN OUT

OSC L IN

VL V -V

F I V

To guarantee sufficient output current, peakinductor current must be lower than the FR9886high-side MOSFET current limit. The peakinductor current is as below:

LPEAK OUT(MAX)

II =I +

2

Ceramic Capacitor

VOUT GND

L=10uH

L=6.8uH

L=4.7uH

VOUT=3.3V, FOSC=340KHz

Probe Ground


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Feedforward Capacitor Selection

Internal compensation function allows users savingtime in design and saving cost by reducing thenumber of external components. The use of afeedforward capacitor C6 in the feedback network isrecommended to improve the transient response orhigher phase margin.

FR9886

VOUT

FB

R1

R2

C6

For optimizing the feedforward capacitor, knowing thecross frequency is the first thing. The crossfrequency (or the converter bandwidth) can bedetermined by using a network analyzer. Whengetting the cross frequency with no feedforwardcapacitor identified, the value of feedforwardcapacitor C6 can be calculated with the following

equation:

CROSS

1 1 1 1C6 -

2 F R1 R1 R2

Where FCROSS is the cross frequency.

To reduce transient ripple, the feedforward capacitorvalue can be increased to push the cross frequencyto higher region. Although this can improvetransient response, it also decrease phase marginand cause more ringing. In the other hand, if morephase margin is desired, the feedforward capacitorvalue can be decreased to push the cross frequency

to lower region.External Boost Diode Selection

For 5V input applications, it is recommended to addan external boost diode. This helps improving theefficiency. The boost diode can be a low cost onesuch as 1N4148.

FR9886

VIN BOOSTVIN

LX

D1

1N4148

5V

C4

PCB Layout Recommendation

The devices performance and stability isdramatically affected by PCB layout. It isrecommended to follow these generalguidelines show as below:

1. Place the input capacitors and outputcapacitors as close to the device aspossible. Trace to these capacitorsshould be as short and wide as possible tominimize parasitic inductance andresistance.

2. Place feedback resistors close to the FBpin.

3. Keep the sensitive signal (FB) away fromthe switching signal (LX).

4. The exposed pad of the package should besoldered to an equivalent area of metal onthe PCB. This area should connect to theGND plane and have multiple viaconnections to the back of the PCB as wellas connections to intermediate PCB layers.The GND plane area connecting to theexposed pad should be maximized to

improve thermal performance.

5. Multi-layer PCB design is recommended.

1 2 3 4

5678

L1LX

GND

VOUTVIN

Exposed

PadGND

C4

C5

R1

R2R3

C3

C6

C2

+

C1

+

Figure 23. FR9886 SOP-8(Exposed Pad)

package CIN/COUT with EC capacitorsRecommended PCB Layout Diagram


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Outline Information

SOP- 8 Package (Unit: mm)

.NoteFollowed from JEDEC MO-012-E

SYMBOLSUNIT

DIMENSION IN MILLIMETER

MIN MAX

A 1.40 1.75

A1 0.10 0.25

A2 1.30 1.50

B 0.31 0.51

D 4.80 5.00

E 3.80 4.00

e 1.20 1.34

H 5.80 6.20

L 0.40 1.27

Carrier dimensions


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Outline Information

SOP- 8 (Exposed Pad) Package (Unit: mm)

SYMBOLSUNIT

DIMENSION IN MILLIMETER

MIN MAX

A 1.25 1.70

A1 0.00 0.15

A2 1.25 1.55

B 0.31 0.51

D 4.80 5.00

D1 1.82 3.35

E 3.80 4.00

E1 1.82 2.41

e 1.20 1.34

H 5.80 6.20

L 0.40 1.27

NoteFollowed From JEDEC MO-012-E.

Carrier dimensions

Life Support Policy

Fitipowers products are not authorized for use as critical components in life support devices or other medical systems.

data sheet ic fr9886

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