concept kit:pwm boost converter transients model

Concept Kit:PWM Boost Converter

Transients Model

All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 1

Power Switches(Semiconductor)

Filter & LoadPWM IC (Voltage Mode)

VREF

+-

VOUTL1 2

C

Rload

Vo

ESROSC

REF

E / A

Comp

+

-

-

+

U?PWM_IC

FOSC = 52K

VP = 2.5VREF = 1.23

pwm

+ -

+ - S1S

RON = 100m

D1DIODE

Contents

1. The PWM Boost Converter Topology

2. Power Switches (Semiconductor)

3. Boost Converter Design Workflow

Setting PWM Controller’s Parameters

Setting Output Voltage: Rupper, Rlower

Inductor Selection: L

Capacitor Selection: C, ESR

Setting the Compensator Parameters

4. Boost Converter Simulation (Example)

4.1 Switching Waveforms

4.2 Power State Switches Voltage and Current

5. Load Transient Response Simulation (Example)

6. Boost Converter Reliability Testing (Example)

7. Converter Efficiency

7.1 Converter Efficiency vs. MOSFET, Rds(on)

7.2 Converter Efficiency vs. DIODE, VF

8. Simulation Using Real Device Models (Example)

8.1 Switching Waveforms (Real Device Models)

8.2 Converter Efficiency (Real Device Models)

9. SpicePark of MOSFET Model

Simulation Index


1

2

3

4

5

C

D1DIODE

+

-

+

-

S1 S

RON = 0.01R

v out

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = {f osc}

VP = {Vp}VREF = {Vref }

C1

C2

R1R2

C3

RLs

Rlower

Vin

ESR

Rupper

L

0

0

err

1.The PWM Boost Converter Topology


Power Stage: Boost topology

Error Amplifier

Type 3 Compensator*

* Please see appendix B for the detailVoltage Mode

D

BOOST_SW

D

VIN

+

-

VOUT

+

-

IIN IOUT• A Near-Ideal DIODE can be modeled by

using SPICE primitive model (D), which

parameters are : N=0.01 RS=0 CJO=1p.

• A near-ideal MOSFET can be modeled by using PSpice VSWITCH that is voltage

controlled switch. (the default parameters are Roff=1e7 Ron=0.01 Voff=1.47V

Von=1.5V)

D1DIODE

+

-

+

-

S1 S

RON = 0.01

pwm

2.Power Switches (Semiconductor)


(MOSFET)

The parameter RON represents Rds(on) characteristics of MOSFET (usually provide by the manufacturer datasheet).

D

BOOST_SW

D

VIN

+

-

VOUT

+

-

IIN IOUT

D

BOOST_SW

D

VIN

+

-

VOUT

+

-

IIN IOUT

D

BOOST_SW

D

VIN

+

-

VOUT

+

-

IIN IOUT

3.Boost Convertor Design Workflow

The Purpose of the Circuit Simulation

• To Evaluate and Verify the Design of the PWM Boost Converter.

• To Optimize the Parameters of the PWM Boost Converter.


Setting PWM Controller’s Parameters: FOSC , VREF, VP1

Setting Output Voltage: Rupper, Rlower2

Inductor Selection: L3

Capacitor Selection: C, ESR4

Setting the Compensator Parameters: R2, C1, C25

Continue next slide

Boost Convertor Design Workflow


Evaluations:

• Switching Waveforms,

• Power State Switches Voltage and Current,

• Load Step Transient Response,

• and so on

Reliability: L sweep (example)

Evaluations:

• Converter Efficiency vs. MOSFET, Rds(on)

• Converter Efficiency vs. Diode, VF

Evaluations Using Real Device Models (as an Option)

C

D1DIODE

+

-

+

-

S1 S

RON = 0.01R

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = {f osc}


C1

C2

R1 R2

C3

RLs

Rlower

Vin

ESR

Rupper

L

0

0

err

v out

Boost Convertor Design Workflow


1

2

3

4

5

Type 3 Compensator*

5

Voltage Mode

Design Specification (Example)

A boost converter is designed to deliver 12V, 1.5A from a 3.3 V battery

Step-Up (Boost) Converter :

• Vin,max = 3.63 (V)

• Vin,min = 2.97 (V)

• Vout = 12 (V)

• Vout, ripple = 180mVP-P (1.2%)

• Io,max = 1.5 (A)

• Io,min = 0.2 (A)

Control IC :

• Part # TPS43000 (PWM Controller IC)

• Switching Frequency – fosc = 300 (kHz)


Vin = 3.310%

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = 300K

VP = 2.2VREF = 0.8

Setting PWM Controller’s Parameters


comp

PWM

FB

1

• FOSC, Oscillation frequency (frequency of the

sawtooth signal).

• VREF, feedback reference voltage, value is

given by the datasheet

• VP = the sawtooth peak voltage.

• If VP does not provided, it could be calculated from:

VP = VFB /d

VFB = VFBH – vFBL

d = dMAX – dMIN

where

vFBH is maximum FB voltage where d = 0

vFBL is minimum FB voltage where d =1(100%)

dMAX is maximum duty cycle, e.g. d = 0(0%)

dMIN is minimum duty cycle, e.g. d =1(100%)

The Comparator compares the error voltage

(between FB and REF) with a sawtooth signal

(frequency = FOSC, peak saw voltage =

VP) to generate PWM signal, as shown in the

figure below.

Time

V(PWM)

V(osc) V(comp)

0V

2.0V

3.0V

SEL>>VP

Duty cycle (d) is a value from 0 to 1

f = FOSC

If vFBH and vFBL are not provided, the default value, VP=2 could be used.

(eq.1)

Setting PWM Controller’s Parameters (Example)

So we’ve got

VREF = 0.8


The VREF value is given by the datasheet

TPS43000 electrical characteristics

1

The switching frequency 300kHz constant is chosen

Input

FOSC = 300k

Setting PWM Controller’s Parameters (Example)

from the (eq.1)

VP = VFB /d

• from the datasheet , VFB = (2-0) = 2V, and d = (0.9-0) = 0.9

VP = 2 / 0.9

= 2.2


The VP ( sawtooth signal amplitude ) can be calculated from the characteristics below.

TPS43000 electrical characteristics

1

• Use the following formula to select the resistor values.

Example

Given: Vout = 12V

Vref = 0.8

Rlower = 10k

then:

Rupper = 140k

Setting Output Voltage: Rupper, Rlower


lower

upperREFOUT

R

RVV 1

2

REF

lowerREFOUTupper

V

RVVR

)(

(eq.2)

Inductor Selection: L, RLS


Inductor Value

• The output inductor value is selected to set the

converter to work in CCM (Continuous Current

Mode) for all load current conditions.

• Calculated by

• with

Where

• LCCM is the inductor that make the converter to work in CCM.

• Dmin is the minimum duty cycle; Dmin =1- Vin,max /VOUT

• Dmax is the maximum duty cycle; Dmax =1- Vin,min /VOUT

• RLs is load resistance at the minimum output current ( Io,min )

• fosc is switching frequency

• IL is inductor ripple current

min,

2minmin

2

)1(

Oosc

OUTCCM

If

VDDL

3

osc

inL

fL

DVI

maxmin,

C

D1DIODE

+

-

+

-

S1 S

RON = 0.01R

pwm

RLs

ESR

L

(eq.3)

(eq.4)

Inductor Selection: L, RLS (Example)


Inductor Value

from (eq.3)

Given:

• Vin,max = 3.63V (3.3V+10%), Vout = 12V, Io,min = 0.2A

• Dmin = 1- Vin,max /Vout = 0.7

• fosc = 300kHz

Then:

• LCCM 6.4 (uH),

• L = 6.8 (uH) is selected

3

min,

2minmin

2

)1(

Oosc

OUTCCM

If

VDDL

C

D1DIODE

+

-

+

-

S1 S

RON = 0.01R

pwm

RLs

ESR

L

Capacitor Selection: C, ESR


Capacitor Value

• The minimum allowable output capacitor

value should be determined by

• In addition, the capacitor must be able to handle the current more than

• The ESR of the output capacitor adds some more ripple, so it should be limited by

following equation:

OSCrippleout

o

fV

IDC

,

max,max

C

rippleout

I

VESR

,

4

2,

LRatedC

II

• Where IL is calculated by the (eq.4)

(eq.5)

(eq.6)

(eq.7)

C

D1DIODE

+

-

+

-

S1 S

RON = 0.01R

pwm

RLs

ESR

L

Capacitor Selection: C, ESR (Example)


Capacitor Value

From the (eq.5)

and the (eq.6) and (eq.7)

Given:

• Dmax = 0.75 V

• Io, max = 1.5 A

• Vout,ripple = 0.18 V

Then:

• C 20.9 (F)

In addition:

• IC,Rated ≈ 550mA ESR 27m

C

rippleout

I

VESR

,

4

OSCRippleout

o

fV

IDC

,

max,max

2

LC

II

C

D1DIODE

+

-

+

-

S1 S

RON = 0.01R

pwm

RLs

ESR

L

C

D1DIODE

+

-

+

-

S1 S

RON = 0.01R

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = {f osc}


Type 3 Compensator v out

C1

C2

R1R2

C3

RLs

Rlower

Vin

ESR

Rupper

L

0

0

err

• Loop gain for this configuration is

• The purpose of the compensator G(s)

is to tailor the converter loop gain

(frequency response) to make it stable

when operated in closed-loop

conditions.

• The element of the Type 3 compensator (C1, C2 , C3 , R1, and R2 ) can be extracted

by using Boost_Calculator.xls (Excel sheet) and open-loop simulation with the

Average Models (ac models).


PWMGsGsHsT )()()(

GPWM

Compensator: G(s)

Power stage: H(s)

Stabilizing the Converter5

Remark: The Average Models are not included with this package.

Specification:

VIN = 3.3V 10%

VOUT = 12V

IOUT = 0.2 ~ 1.5A

PWM Controller:

fOSC = 300kHz

VREF = 0.8V

VP1 = 2.2V

Rlower = 10k,

Rupper = 140k,

L = 6.8uH (RLS=10m ),

C = 1410uF (ESR = 27m),

Task:

•Voltage and Current Waveforms Evaluation.

4.Boost Converter Simulation (Example)


Characteristics from Texas Instruments IC: TPS43000.

2

*Analysis directives:

.TRAN 0 10ms 0ms 100n

.OPTIONS ABSTOL= 1.0n

.OPTIONS CHGTOL= 0.01u

.OPTIONS ITL1= 200

.OPTIONS ITL2= 100

.OPTIONS ITL4= 50

.OPTIONS RELTOL= 0.01

D1DIODE

+

-

+

-

S1 S

RON = 0.01

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = 300k

VP = 2.2VREF = 0.8

C1

8.259n

C2795p

R1

47.9k

R24.9k

C3

2.826nF

RLs10m

v out

Rlower10k

Vin

3.3

ESR

27m

C

1410u

Rupper140k

L6.8u

0

0

err

R

12

• The simulation results shows waveforms of the boost converter.

• Output ripple voltage (caused by ESR) = 116mVP-P.


Control Voltage

V(PWM)

VOUT, RIPPLE

Inductor Current

I(L)

Switch Current

ID(S1)

Time

9.980ms 9.984ms 9.988ms 9.992ms 9.996ms 10.000ms

v(vout)

11.8V

12.0V

12.1V

12.2V

SEL>>(9.986m,11.970)

(9.982m,12.086)

I(L)

0A

2.5A

5.0A

I(S1:3)

0A

2.5A

5.0A

v(pwm)

0V

5.0V

4.1 Switching Waveforms

Time

9.990ms 9.992ms 9.994ms 9.996ms 9.998ms 10.000ms

1 V(D1:A,D1:C) 2 I(D1)

-16V

-8V

0V

8V

16V1

>>

-5.0A

-2.5A

0A

2.5A

5.0A2

(9.996m,4.3554)

(9.993m,-11.940)

1 V(S1:3,S1:4) 2 I(S1:3)

0V

4V

8V

12V

16V1

SEL>>

0A

1.5A

3.0A

4.5A

6.0A2

SEL>>

(9.996m,4.3125)(9.992m,12.095)


4.2 Power State Switches Voltage and Current

• Switch (MOSFET) has the steady state voltage: VDS, PEAK = 12.095V and

current: ID, PEAK = 4.312A

• Diode has the steady state voltage: VAK, PEAK = -11.940V and current: IF, PEAK

= 4.355A

SW (MOSFET) Voltage VDS

SW (MOSFET) Current ID

Diode Voltage VAK

Diode Forward Current IF

D1DIODE

+

-

+

-

S1 S

RON = 0.01

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = 300k

VP = 2.2VREF = 0.8

C1

8.259n

C2795p

R1

47.9k

R24.9k

C3

2.826nF

RLs10m

v out

Rlower10k

Vin

3.3

ESR

27m

C

1410u

Rupper140k

L6.8u

0

0

err

I1

TD = 19m

TF = 10uPW = 2mPER = 1

I1 = 0.2I2 = 1.5

TR = 10u


The converter are connected with step-load to perform load transient response simulation.


.TRAN 0 26ms 18ms 100n



.OPTIONS ITL1= 200

.OPTIONS ITL2= 100

.OPTIONS ITL4= 50


Iload = 0.2A step to 1.5A

5.Load Transient Response Simulation (Example)

Time

18ms 20ms 22ms 24ms 26ms

v(vout)

11.8V

11.9V

12.0V

12.1V

12.2V

SEL>>

(21.022m,12.162)

(19.099m,11.912)

I(I1)

0A

0.4A

0.8A

1.2A

1.6A

2.0A


5.Load Transient Response Simulation (Example)

• The simulation results shows output voltage change waveforms caused by

step load current.

0.2-1.5A Step load current

Output Voltage Change

D1DIODE

+

-

+

-

S1 S

RON = 0.01

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = 300k

VP = 2.2VREF = 0.8

C1

8.259n

C2795p

R1

47.9k

R24.9k

C3

2.826nF

RLs10m

v out

Rlower10k

Vin

3.3

ESR

27m

C

1410u

Rupper140k

0

L{L}

0

err

R

60

PARAMETERS:

L = 6.8u

Specification:

VIN = 3.3V 10%

VOUT = 12V

IOUT = 0.2 ~ 1.5A

PWM Controller:

fOSC = 300kHz

VREF = 0.8V

VP1 = 2.2V

Rlower = 10k,

Rupper = 140k,

L = Swept parameter (RLS=10m ),

C = 1410uF (ESR = 27m),

Task:

•To check that the converter still work in CCM

after 15% reduction of the inductor value.

6.Boost Converter Reliability Testing (Example)


2


.TRAN 0 20ms 0 100n

.STEP PARAM L LIST 6.8u, 5.78u



.OPTIONS ITL1= 200

.OPTIONS ITL2= 100

.OPTIONS ITL4= 50


Iload, min

= 0.2A

Time

19.990ms 19.992ms 19.994ms 19.996ms 19.998ms 20.000ms

v(vout)

12.04V

11.98V

SEL>>

I(L)

0A

0.8A

1.6A

I(S1:3)

0A

1.0A

2.0A

v(pwm)

0V

5.0V


6.Boost Converter Reliability Testing (Example)

• The simulation results shows waveforms of the converter at L=6.8uH and 5.78uH

• At L = 5.78uH(-15%), the converter still work in CCM

A: V(PWM),

D: VOUT, RIPPLE

C: I(L)

B: ID(S1)

the converter works in CCM (no zero current) at L=5.78uH.

L=6.8uH

L=5.78uH

D1DIODE

+

-

+

-

S1 S

RON = {Rdson}

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = 300k

VP = 2.2VREF = 0.8

C1

8.259n

C2795p

R1

47.9k

R24.9k

C3

2.826nF

RLs10m

v out

Rlower10k

Vin

3.3

ESR

27m

C

1410u

Rupper140k

L6.8u

0

0

err

R

12

PARAMETERS:

Rdson = 0.1

7.1 Converter Efficiency vs. MOSFET Rds(on)


Perform transient simulation to measure the converter efficiency at Rds(on)= 0.01 and 0.1 .


.TRAN 0 20ms 18.8m 100n

.STEP PARAM Rdson LIST 0.01, 0.1



.OPTIONS ITL1= 200

.OPTIONS ITL2= 100

.OPTIONS ITL4= 50


Time

19.50ms 19.55ms 19.60ms 19.65ms 19.70ms 19.75ms 19.80ms 19.85ms 19.90ms 19.95ms

100*AVG(W(R))/AVG(-W(Vin))

50

60

70

80

90

100

(19.750m,88.600)

(19.750m,97.343)


7.1 Converter Efficiency vs. MOSFET Rds(on)

• The converter efficiency is decreased from 97.3% to 88.6% when

Rds(on) increase from 0.01 to 0.1.

Efficiency (%)

Rds(on) = 0.01, Efficiency = 97.3 %

Rds(on) = 0.1, Efficiency = 88.6 %

Rds(on) = 0.01

Rds(on) = 0.1

D1DIODE

+

-

+

-

S1 S

RON = 0.01

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = 300k

VP = 2.2VREF = 0.8

C1

8.259n

C2795p

R1

47.9k

R24.9k

C3

2.826nF

RLs10m

v out

Rlower10k

Vin

3.3

ESR

27m

C

1410u

Rupper140k

0

L6.8u

0

err

R

12

PARAMETERS:

N = 0.01

7.2 Converter Efficiency vs. Diode, VF


Perform transient simulation to measure the converter efficiency at DIODE (N) = 0.01 and 0.4

V_V1

0V 0.12V 0.24V 0.36V 0.48V 0.60V 0.72V 0.84V 0.96V 1.08V

I(D1)

0A

0.1A

0.2A

0.3A

0.4A

0.5A

0.6A

0.7A

0.8A

0.9A

1.0A

VF increases when DIODE (N) increases.

VF

Diode Forward I – V Characteristics

Diode Forward Voltage vs. Diode model parameter: N


.TRAN 0 20ms 18.8m 100n

.STEP PARAM N LIST 0.01, 0.4



.OPTIONS ITL1= 200

.OPTIONS ITL2= 100

.OPTIONS ITL4= 50


Time

19.50ms 19.55ms 19.60ms 19.65ms 19.70ms 19.75ms 19.80ms 19.85ms 19.90ms 19.95ms

100*AVG(W(R))/AVG(-W(Vin))

50

60

70

80

90

100

(19.750m,94.663)

(19.750m,97.343)


7.2 Converter Efficiency vs. Diode, VF

Efficiency (%)

DIODE (N) = 0.01, Efficiency = 97.3 %

DIODE (N) = 0.4, Efficiency = 94.6 %

• The converter efficiency is decreased from 97.3% to 94.7% when

DIODE’s parameter N increase from 0.01 to 0.4

pwm

OSCREF

E / A

Comp

+

-

-

+

U1PWM_IC

FOSC = 300k

VP = 2.2VREF = 0.8

C1

8.259n

C2795p

R1

47.9k

R24.9k

C3

2.826nF

RLs10m

v out

Rlower10k

Vin

3.3

ESR

27m

C

1410u

Rupper140k

0

L6.8u

0

err

R

12

U2TPC6005S

D1

M2FM3

8.Simulation Using Real Device Models (Example)


As we can see in the efficiency simulation (topic #7) that’s how the switching devices effect

the simulation result. For the accurate simulation result, the accurate models, that relate to

the real devices characteristics, are needed.

The Real Device Models of MOSFET (Toshiba N Channel MOS Part# TPCP6005)

The Real Device Models of Schottky Diode (Shindengen SBD Part# M2FM3)

• The real device model enable designers to include the spike signal

(caused by the devices’ parasitic capacitance) in the switching

waveforms simulation.


Time

9.980ms 9.985ms 9.990ms 9.995ms 10.000ms

V(VOUT)

11.9V

12.0V

12.1V

SEL>>

I(L)

0A

2.0A

4.0A

6.0A

I(U2:1)

-2.0A

0A

2.0A

4.0A

6.0A

V(PWM)

0V

5.0V

Spike current

8.Simulation Using Real Device Models (Example)

Time

9.0ms 9.1ms 9.2ms 9.3ms 9.4ms 9.5ms 9.6ms 9.7ms 9.8ms 9.9ms 10.0ms

100* AVG(W(R))/ AVG(-W(Vin))

50

60

70

80

90

100

(9.500m,89.973)


8.2 Converter Efficiency (Real Device Models)

• The converter efficiency is decreased from 97.3% to 89.97% when the

device models are changed from the near-Ideal to the real model.

Efficiency (%)

Efficiency = 89.97 %

• After the device voltage and current condition is simulated (e.g. VDS, PEAK=12.095V and

ID, PEAK=4.312A), The real device models could be picked up from the SpicePark, that

is the resource of device models, provided by Bee Technologies.


Maximum Value Device Models

9.SpicePark of MOSFET Model

Simulation Index


Simulations Folder name

1. Switching Waveforms......................................................

2. Power Stage Switches Voltage and Current....................

3. Load Transient Response................................................

4. Boost Converter Reliability Testing...................................

5. Converter Efficiency vs. MOSFET Rds(on) ....................

6. Converter Efficiency vs. MOSFET Diode, VF..................

waveforms

powersw

stepload

optimize

efficiency-rdson

efficiency-diode

Libraries :

1. ..\pwmic.lib

2. ..\diode.lib

concept kit:pwm boost converter transients model

Technology

pwm boost converter

pwm signal

semiconductor pwm

sw boost

voltage d ron

boost topologyd1rlsldiodev

c255c1r1r2errrupper

setting output voltage