Concept Kit:PWM Boost Converter Transients Model

PWM IC Power Switches Filter & Load
(Voltage Mode)
U?
(Semiconductor)
PWM_IC RON = 100m
1
L
2 Vo
VOUT
-
-

+ E/A S1 D1 C

-
+

+
+
Comp S DIODE

+
-
- Rload
OSC pwm
REF ESR

FOSC = 52K
VREF VREF = 1.23
VP = 2.5

Concept Kit:
PWM Boost Converter
Transients Model
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 1

Contents
1. The PWM Boost Converter Topology
2. Power Switches (Semiconductor)
3. Boost Converter Design Workflow
1 Setting PWM Controller’s Parameters
2 Setting Output Voltage: Rupper, Rlower
3 Inductor Selection: L
4 Capacitor Selection: C, ESR
5 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.The PWM Boost Converter Topology
Power Stage: Boost topology
D1
RLs L DIODE
v out

S1 S
Vin + +
pwm C
- -
R
RON = 0.01 ESR

Error Amplifier
C2
0

C1 R1
err R2
Rupper
U1
PWM_IC
C3
- Type 3 Compensator*
+ E/A
+ Rlower
Comp
- OSC
REF

FOSC = {f osc} 0
Voltage Mode VREF = {Vref }
VP = {Vp}
* Please see appendix B for the detail


2.Power Switches (Semiconductor)

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

IIN IN
I IIN
IIN BOOST_SW
BOOST_SW
D1
DIODE IOUT
BOOST_SW •
BOOST_SW IOUT IOUT A Near-Ideal
IOUT DIODE can be modeled by
using SPICE primitive model (D), which
++ ++ DD D ++
D + parameters are : N=0.01 RS=0 CJO=1p.
+
S1 S
+ +
pwm • A near-ideal MOSFET can be modeled by
VIN IN
V VIN
VIN - -
VOUT VOUT
VOUT VOUT
using PSpice VSWITCH that is voltage
D
RON = 0.01D D D controlled switch. (the default parameters
-- -- (MOSFET) -- --
are Roff=1e7 Ron=0.01 Voff=1.47V
Von=1.5V)


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.

1 Setting PWM Controller’s Parameters: FOSC , VREF, VP


3 Inductor Selection: L


5 Setting the Compensator Parameters: R2, C1, C2

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)


Boost Convertor Design Workflow

3 D1
RLs L DIODE
v out

S1 S
Vin + +
pwm C
- -
R
RON = 0.01 ESR

4 Type 3 Compensator*

0
C2 5
5
C1 R1 R2
err Rupper

U1
PWM_IC C3

-
+ E/A
+ Rlower
Comp
-
OSC 2
REF

FOSC = {f osc} 0
1
Voltage Mode VREF = {Vref }
VP = {Vp}


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 = 3.310%
• 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)


1 Setting PWM Controller’s Parameters
U1
PWM_IC
comp
• FOSC, Oscillation frequency (frequency of the
sawtooth signal).
- FB

PWM
Comp
+ E/A
+ • VREF, feedback reference voltage, value is
- OSC given by the datasheet
REF

FOSC = 300K • VP = the sawtooth peak voltage.
VREF = 0.8
VP = 2.2 • If VP does not provided, it could be calculated from:
The Comparator compares the error voltage VP = VFB /d (eq.1)
(between FB and REF) with a sawtooth signal
(frequency = FOSC, peak saw voltage = VFB = VFBH – vFBL
VP) to generate PWM signal, as shown in the
figure below.
d = dMAX – dMIN
where
f = FOSC
3.0V
vFBH is maximum FB voltage where d = 0
2.0V
vFBL is minimum FB voltage where d =1(100%)
SEL>>
VP
0V dMAX is maximum duty cycle, e.g. d = 0(0%)
V(osc) V(comp)

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

 If vFBH and vFBL are not provided, the default value, VP=2 could be used.
V(PWM) Duty cycle (d) is a value from 0 to 1
Time


1 Setting PWM Controller’s Parameters (Example)
The switching frequency 300kHz constant is chosen
Input
FOSC = 300k

The VREF value is given by the datasheet

TPS43000 electrical characteristics

So we’ve got
VREF = 0.8


1 Setting PWM Controller’s Parameters (Example)

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

TPS43000 electrical characteristics

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



• Use the following formula to select the resistor values.

 Rupper 
VOUT  VREF 1   (eq.2)
 Rlower 

Example
Given: Vout = 12V
Vref = 0.8
Rlower = 10k
then: (VOUT  VREF )  Rlower
Rupper 
VREF
Rupper = 140k


3 Inductor Selection: L, RLS

Inductor Value
• The output inductor value is selected to set the
D1
RLs L DIODE converter to work in CCM (Continuous Current
Mode) for all load current conditions.
S1 S
+ +
pwm C • Calculated by
- -
D min (1  D min) 2 VOUT

R
RON = 0.01 ESR LCCM (eq.3)
2  fosc  IO , min
Vin, min D max
• with IL  (eq.4)
L  fosc
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


3 Inductor Selection: L, RLS (Example)

D1
Inductor Value
RLs L DIODE

S1 S
+ +
pwm C from (eq.3)
- -

D min (1  D min) 2 VOUT
R
RON = 0.01 ESR

LCCM 
2  fosc  IO , min

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


D1
RLs L DIODE Capacitor Value
S1 S
• The minimum allowable output capacitor
+ +
pwm C value should be determined by
- -

D max Io, max
R
RON = 0.01 ESR

C (eq.5)
Vout, ripple fOSC
• In addition, the capacitor must be able to handle the current more than
IL
IC , Rated  (eq.6)
2
• Where IL is calculated by the (eq.4)
• The ESR of the output capacitor adds some more ripple, so it should be limited by
following equation:
Vout , ripple
ESR  (eq.7)
IC


4 Capacitor Selection: C, ESR (Example)
D1
DIODE
Capacitor Value
1 S From the (eq.5) D max Io, max
pwm C C
Vout, Ripple fOSC
+
-
R
ON = 0.01 ESR
and the (eq.6) and (eq.7)
IL Vout , ripple
IC  ESR 
2 IC
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


5 Stabilizing the Converter
• Loop gain for this configuration is
RLs L
D1
DIODE
Power stage: H(s)

S1 S
Vin + +
pwm C
- -
R

T ( s)  H ( s)  G ( s)  GPWM RON = 0.01 ESR

Compensator: G(s)
Type 3 Compensator v out
C2
0

C1 R1
err R2
Rupper
• The purpose of the compensator G(s) U1
PWM_IC
C3
is to tailor the converter loop gain -
+
(frequency response) to make it stable Comp
E/A
+ Rlower
- OSC
when operated in closed-loop GPWM
REF

conditions. FOSC = {f osc}
VREF = {Vref }
0

VP = {Vp}

• 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).

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


4.Boost Converter Simulation (Example)
RLs L D1
10m 6.8u DIODE
Specification: v out

VIN = 3.3V 10% S1 S ESR
+ pwm 27m
VOUT = 12V Vin
3.3 -
+
- R
12
IOUT = 0.2 ~ 1.5A RON = 0.01
C
1410u

PWM Controller: C2
2
0 795p
fOSC = 300kHz
R2
VREF = 0.8V Characteristics from err
C1 R1
Rupper
4.9k

VP1 = 2.2V Texas Instruments IC: U1 8.259n 47.9k
140k
C3
TPS43000. PWM_IC
2.826nF
-

Rlower = 10k, Comp
+ E/A
+
-
Rlower
Rupper = 140k, OSC
REF
10k

L = 6.8uH (RLS=10m ), FOSC = 300k
VREF = 0.8 0
C = 1410uF (ESR = 27m), VP = 2.2

*Analysis directives:
.TRAN 0 10ms 0ms 100n
.OPTIONS ABSTOL= 1.0n
.OPTIONS CHGTOL= 0.01u
Task: .OPTIONS ITL1= 200
.OPTIONS ITL2= 100
•Voltage and Current Waveforms Evaluation. .OPTIONS ITL4= 50
.OPTIONS RELTOL= 0.01


4.1 Switching Waveforms

5.0V
Control Voltage
V(PWM)
0V
v(pwm)
5.0A
Switch Current
ID(S1) 2.5A

0A
I(S1:3)
5.0A
Inductor Current
I(L) 2.5A

0A
I(L)
12.2V
(9.982m,12.086)
12.1V
VOUT, RIPPLE 12.0V
SEL>> (9.986m,11.970)
11.8V
9.980ms 9.984ms 9.988ms 9.992ms 9.996ms 10.000ms
v(vout)
Time

• The simulation results shows waveforms of the boost converter.
• Output ripple voltage (caused by ESR) = 116mVP-P.


4.2 Power State Switches Voltage and Current
16V 6.0A
1 2
(9.992m,12.095)
(9.996m,4.3125)
SW (MOSFET) Voltage VDS
12V 4.5A

8V 3.0A
SW (MOSFET) Current ID

4V 1.5A

SEL>>
0V 0A
1 V(S1:3,S1:4) 2 I(S1:3)
16V 5.0A
1 2
Diode Forward Current IF
8V 2.5A
(9.996m,4.3554)

0V 0A

(9.993m,-11.940)
-8V -2.5A
Diode Voltage VAK
>>
-16V -5.0A
9.990ms 9.992ms 9.994ms 9.996ms 9.998ms 10.000ms
1 V(D1:A,D1:C) 2 I(D1)
Time

• 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


5.Load Transient Response Simulation (Example)
The converter are connected with step-load to perform load transient response simulation.
RLs L D1
10m 6.8u DIODE
v out

S1 S ESR
+ pwm 27m I1 = 0.2 I1
Vin +
I2 = 1.5
3.3 - -
TD = 19m
RON = 0.01 TR = 10u
C TF = 10u
1410u PW = 2m
PER = 1 Iload = 0.2A
C2
step to 1.5A
0 795p

R2
C1 R1 4.9k
err Rupper
140k
U1 8.259n 47.9k C3
PWM_IC
2.826nF
*Analysis directives: -
+ E/A
.TRAN 0 26ms 18ms 100n Comp
+
Rlower
-
.OPTIONS ABSTOL= 1.0n OSC
REF
10k

.OPTIONS CHGTOL= 0.01u
FOSC = 300k
.OPTIONS ITL1= 200 VREF = 0.8 0
VP = 2.2
.OPTIONS ITL2= 100
.OPTIONS ITL4= 50


5.Load Transient Response Simulation (Example)
2.0A

1.6A 0.2-1.5A Step load current

1.2A

0.8A

0.4A

0A
I(I1)
12.2V
Output Voltage Change
12.1V (21.022m,12.162)

12.0V

11.9V

SEL>> (19.099m,11.912)
11.8V
18ms 20ms 22ms 24ms 26ms
v(vout)
Time

• The simulation results shows output voltage change waveforms caused by
step load current.


6.Boost Converter Reliability Testing (Example)
RLs L D1
Specification: 10m {L} DIODE
v out

VIN = 3.3V 10% PARAMETERS:
L = 6.8u S1 S ESR
VOUT = 12V Vin + +
pwm 27m
R
3.3 - -

IOUT = 0.2 ~ 1.5A RON = 0.01
60
C
1410u
Iload, min
PWM Controller: 2 = 0.2A
C2
fOSC = 300kHz 0 795p

R2
VREF = 0.8V C1 R1 4.9k
err Rupper
VP1 = 2.2V 140k
U1 8.259n 47.9k C3
PWM_IC
2.826nF

Rlower = 10k,
-
+ E/A
+
Comp
Rupper = 140k, - OSC
Rlower
10k
REF
L = Swept parameter (RLS=10m ),
FOSC = 300k
0
C = 1410uF (ESR = 27m), VREF = 0.8
VP = 2.2
*Analysis directives:
.TRAN 0 20ms 0 100n
.STEP PARAM L LIST 6.8u, 5.78u
.OPTIONS ABSTOL= 1.0n
Task: .OPTIONS CHGTOL= 0.01u
• To check that the converter still work in CCM .OPTIONS ITL1= 200
.OPTIONS ITL2= 100
after 15% reduction of the inductor value. .OPTIONS ITL4= 50


6.Boost Converter Reliability Testing (Example)

5.0V
L=6.8uH
A: V(PWM), L=5.78uH
0V
v(pwm)
2.0A
B: ID(S1)
1.0A

0A
I(S1:3)
1.6A
C: I(L)
0.8A

0A
I(L) the converter works in CCM (no zero current) at L=5.78uH.
12.04V
D: VOUT, RIPPLE
SEL>>
11.98V
19.990ms 19.992ms 19.994ms 19.996ms 19.998ms 20.000ms
v(vout)
Time

• 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


7.1 Converter Efficiency vs. MOSFET Rds(on)
Perform transient simulation to measure the converter efficiency at Rds(on)= 0.01 and 0.1 .
RLs L D1
10m 6.8u DIODE
v out

S1 S ESR
Vin
PARAMETERS: + +
pwm 27m
Rdson = 0.1 R
3.3 - -
12
RON = {Rdson}
C
1410u

C2
0 795p

R2
C1 R1 4.9k
err Rupper
140k
*Analysis directives: U1 8.259n 47.9k C3
.TRAN 0 20ms 18.8m 100n PWM_IC
2.826nF
.STEP PARAM Rdson LIST 0.01, 0.1 -
.OPTIONS ABSTOL= 1.0n + E/A
.OPTIONS CHGTOL= 0.01u Comp
+
Rlower
.OPTIONS ITL1= 200 - OSC 10k
REF
.OPTIONS ITL2= 100
.OPTIONS ITL4= 50 FOSC = 300k
.OPTIONS RELTOL= 0.01 VREF = 0.8 0
VP = 2.2


7.1 Converter Efficiency vs. MOSFET Rds(on)
Efficiency (%)
100

Rds(on) = 0.01, Efficiency = 97.3 %
(19.750m,97.343)

90

Rds(on) = 0.1, Efficiency = 88.6 %
(19.750m,88.600)
80

70

60
Rds(on) = 0.01
Rds(on) = 0.1

50
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))
Time

• The converter efficiency is decreased from 97.3% to 88.6% when
Rds(on) increase from 0.01 to 0.1.


7.2 Converter Efficiency vs. Diode, VF
Perform transient simulation to measure the converter efficiency at DIODE (N) = 0.01 and 0.4

PARAMETERS:
N = 0.01
RLs L D1
Diode Forward Voltage vs. 10m 6.8u DIODE
v out
Diode model parameter: N
S1 S ESR
+ pwm 27m
Vin +
R
3.3 - -
Diode Forward I – V Characteristics RON = 0.01
12
1.0A C
VF increases when DIODE (N) increases. 1410u
0.9A

0.8A

C2
0.7A 0 795p
0.6A
R2
C1 R1 4.9k
0.5A
err Rupper
0.4A
140k
U1 8.259n 47.9k C3
0.3A
PWM_IC
2.826nF
0.2A
-
*Analysis directives: + E/A
0.1A VF
.TRAN 0 20ms 18.8m 100n
+
Comp
-
Rlower
OSC 10k
0A
0V 0.12V 0.24V 0.36V 0.48V 0.60V 0.72V 0.84V 0.96V 1.08V .STEP PARAM N LIST 0.01, 0.4 REF
I(D1)
V_V1 .OPTIONS ABSTOL= 1.0n
FOSC = 300k
.OPTIONS CHGTOL= 0.01u VREF = 0.8 0
.OPTIONS ITL1= 200 VP = 2.2

.OPTIONS ITL2= 100
.OPTIONS ITL4= 50


7.2 Converter Efficiency vs. Diode, VF
Efficiency (%)
100
DIODE (N) = 0.01, Efficiency = 97.3 % (19.750m,97.343)
(19.750m,94.663)
DIODE (N) = 0.4, Efficiency = 94.6 %
90

80

70

60

50
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))
Time

• The converter efficiency is decreased from 97.3% to 94.7% when
DIODE’s parameter N increase from 0.01 to 0.4


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
Schottky Diode (Shindengen
RLs
10m
L
6.8u
SBD Part# M2FM3)
D1
v out

M2FM3
ESR
Vin 27m
pwm R
3.3
12
U2 C
TPC6005S 1410u

C2
0 795p

The Real Device Models of C1 R1
R2
4.9k
MOSFET (Toshiba N Channel err Rupper
140k
MOS Part# TPCP6005) U1 8.259n 47.9k C3
PWM_IC
2.826nF
-
+ E/A
+
Comp
-
Rlower
OSC 10k
REF

FOSC = 300k
VREF = 0.8 0
VP = 2.2


8.Simulation Using Real Device Models (Example)

5.0V

0V

V(PWM) Spike current
6.0A
4.0A
2.0A
0A
-2.0A
I(U2:1)
6.0A

4.0A

2.0A

0A
I(L)
12.1V

12.0V

SEL>>
11.9V
9.980ms 9.985ms 9.990ms 9.995ms 10.000ms
V(VOUT)
Time

• The real device model enable designers to include the spike signal
(caused by the devices’ parasitic capacitance) in the switching
waveforms simulation.


8.2 Converter Efficiency (Real Device Models)
Efficiency (%)
100

Efficiency = 89.97 % (9.500m,89.973)
90

80

70

60

50
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))
Time

• 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.


9.SpicePark of MOSFET Model
Maximum Value Device Models

• 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.


Simulation Index

Simulations Folder name
1. Switching Waveforms...................................................... waveforms
2. Power Stage Switches Voltage and Current.................... powersw
3. Load Transient Response................................................ stepload
4. Boost Converter Reliability Testing................................... optimize
5. Converter Efficiency vs. MOSFET Rds(on) .................... efficiency-rdson

6. Converter Efficiency vs. MOSFET Diode, VF.................. efficiency-diode

Libraries :
1. ..pwmic.lib
2. ..diode.lib


Concept Kit:PWM Boost Converter Transients Model

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