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Concept Kit:PWM Boost Converter Transients Model
1. 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
2. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 2
3. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 3
4. 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)
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 4
5. 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
2 Setting Output Voltage: Rupper, Rlower
3 Inductor Selection: L
4 Capacitor Selection: C, ESR
5 Setting the Compensator Parameters: R2, C1, C2
Continue next slide
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 5
6. 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)
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 6
7. 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}
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 7
8. 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 = 3.310%
• 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)
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 8
9. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 9
10. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 10
11. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 11
12. 2 Setting Output Voltage: Rupper, Rlower
• 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 12
13. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 13
14. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 14
15. 4 Capacitor Selection: C, ESR
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
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16. 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
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17. 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.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 17
22. 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.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 22
23. 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
.OPTIONS RELTOL= 0.01
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 23
24. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 24
25. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 25
26. 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.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 26
27. 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
.OPTIONS RELTOL= 0.01
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 27
28. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 28
29. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 29
30. 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.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 30
31. 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.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 31
32. 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.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 32
33. 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
All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 33