デザインキット・マイクロコントローラ(U pc494)による降圧回路の解説書
-
Upload
tsuyoshi-horigome -
Category
Technology
-
view
1.032 -
download
3
description
Transcript of デザインキット・マイクロコントローラ(U pc494)による降圧回路の解説書
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 1
Design KitBuck Converter Using PC494
Contents
Slide #
1. Buck Converter using PC494: VIN=12V, [email protected].....................................................................
1.1 Output voltage...................................................................................................................................
1.2 Output current...................................................................................................................................
1.3 Output ripple voltage ........................................................................................................................
1.4 Efficiency……....................................................................................................................................
1.5 Step-load response...........................................................................................................................
2. Basic Operation.......................................................................................................................................
2.1 Output voltage equations..................................................................................................................
2.2 Basic operation waveforms...............................................................................................................
3. Switching Transistor Q1..........................................................................................................................
3.1 Voltage and current stresses............................................................................................................
3.2 Transistor characteristics..................................................................................................................
3.3 Transistor Q1 losses ........................................................................................................................
4. Freewheeling Diode D1 (SBD)…………………………….......................................................................
4.1 Voltage and current stresses............................................................................................................
4.2 Schottky barrier diode (SBD) characteristics....................................................................................
4.3 Freewheeling diode D1 (SBD) losses...............................................................................................
4.4 Schottky barrier diode Standard model…….....................................................................................
5. Output Inductor Value..............................................................................................................................
6. Output Capacitor.....................................................................................................................................
7. Voltage Control Feedback Loop..............................................................................................................
Simulations index..........................................................................................................................................
3
4
5
6
7
8
9
10
11
12
13
14
15-16
17
18
19
20-21
22
23-26
27-29
30-31
32
2All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
1. Buck Converter using PC494: VIN=12V, [email protected]
• VIN = 12V
• VOUT = 5V
• IOUT = 0.15~0.5A , IOUT below 0.15A DCM
• Efficiency = >74% with VIN = 12V, load 0.5A
• Output voltage ripple < 1% VOUT
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 3
Schottky barrier diode (SBD) D1 is simulated using a Professional model.
Lo
8RHB
Vcc
0
Vcc12Vdc
OUT+
Q1Q2SA1680
RB
390 RL10
Rsense
0.25
0
OUT-
0
R14500
U1UPC494 1 2 3 4 5 6 7 8
910
11
12
13
14
15
16
R13.9k
R25.1k
R35.1k
R45.1k
R5240k
R62.4k
R77.5k
0
0
VR11.45k
VR3
2k
0
0
C2
0.01uF
C3100nF
C410u
RV2-1{2k-R1}
0
RV2-2{R1}
0 0
R15100
R16100k
R13
7.5k R11500
C51000pFIC = 0
R815k
R171k
C7100n
PARAMETERS:
R1 = 0.1
C1
+
CoRJJ-35V221MG5-T20
IC = 0
D1
XBS104V14R_P
Time
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10ms
V(OUT+,OUT-)
0V
1.0V
2.0V
3.0V
4.0V
5.0V
6.0V
1.1 Output voltage
• The output voltage is regulated at 5V (RL=10) ,voltage overshoot at startup is 0.6V.
Steady state is reached within 4ms.
4All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
Overshoot voltage
Time to reach steady state
Time
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10ms
I(RL)
0A
100mA
200mA
300mA
400mA
500mA
600mA
1.2 Output current
5All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
Overshoot current
• The output current is 0.5A (RL=10) ,current overshoot at startup is 60mA. Steady
state is reached within 4ms.
Time to reach steady state
Time
7.81ms 7.82ms 7.83ms 7.84ms 7.85ms 7.86ms 7.87ms 7.88ms 7.89ms 7.90ms 7.91ms
V(OUT+,OUT-)
4.80V
4.84V
4.88V
4.92V
4.96V
5.00V
5.04V
5.08V
5.12V
1.3 Output ripple voltage
• The output ripple voltage is less than 1% of the output voltage ( < 50 mVP-P ).
6All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
Output voltage ripple
Time
5ms 6ms 7ms 8ms 9ms 10ms
100*AVG(V(RL:1)*I(RL))/AVG(-I(V1)*V(V1:+))
0
10
20
30
40
50
60
70
80
90
100
1.4 Efficiency
• The efficiency of the converter at VIN=12V and load RL=10 is 74% or more.
(Efficiency = > 74%)
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 7
Efficiency = > 74%
Time
6ms 8ms 10ms 12ms 14ms 16ms 18ms 20ms5ms
V(OUT+,OUT-)
4.5V
5.0V
5.5V
SEL>>
I(IL)
0A
250mA
500mA
750mA
1.5 Step-load response
• Simulation results shows the transient responses, when load current steps up and
steps down.
8All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
250mA / 500mA step-load
-250mV
250mV
Vcc
Q1
D1
L11 2
C1
OUT-
Rload
0
R1
R2
PWM Control
Circuit
+
-
OUT+
Vref2.5V
0
2. Basic Operation
The basic operation of how the output voltage is regulated at the desired voltage level.
• VO is sensed by sampling resistors R1, R2 and compare to a reference voltage Vref in
the Error Amp.
• The error voltage is modulated with a sawtooth waveform.
• Pulse-width-modulator (PWM) output pulse width TON is proportional to the Error Amp
output DC voltage level.
• VOUT ,which is proportional to TON ,is regulated at the desired voltage level.
9All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
-IC(Q1)
I(D1)
I(L1)
V in Vcc VO
Error Amp
PWM output pulse
2.1 Output voltage equations
• R1 and R2 are calculated by follow equation. In practical design a variable resistor
,that is higher than the calculated value ,is chosen for R1.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 10
VinT
TV
ONOUT
VrefR
RRVOUT
2
21
• If the circuit works in continuous conduction mode (CCM) , output voltage and TON
follow the equation below.
(1)
(2)
Time
7.82ms 7.84ms 7.86ms 7.88ms 7.90ms7.81ms 7.91ms
I(Lo:1) I(RL)
0.3A
0.7A
I(D1)
0A
500mA
IE(Q1)
0A
500mA
SEL>>
V(Q1:c)
0V
14V
2.2 Basic operation waveforms
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 11
TON
Vin
-IC(Q1)
I(D1)
I(L1)
/ I(RL)
T
ΟΝΟCC
ΤL
VVΔΙ
1ΟFF
ΟΤ
L
VΔΙ
1I(RL)=VO/Rload
• Simulation result shows the waveforms and magnitude of the current throughout the
circuit.
Lo
8RHB
0
Vcc
Vcc12Vdc
OUT+
Q1Q2SA1680
RB
390 RL10
Rsense
0.25
0
OUT-
0
R14500
U1UPC494 1 2 3 4 5 6 7 8
910
11
12
13
14
15
16
R13.9k
R25.1k
R35.1k
R45.1k
R5240k
R62.4k
R77.5k
0
0
VR11.45k
VR3
2k
0
0
C2
0.01uF
C3100nF
C410u
RV2-1{2k-R1}
0
RV2-2{R1}
0 0
R15100
R16100k
R13
7.5k R11500
C51000pFIC = 0
R815k
R171k
C7100n
PARAMETERS:
R1 = 0.1
C1
+
CoRJJ-35V221MG5-T20
IC = 0
D1
XBS104V14R_P
3. Switching Transistor Q1
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 12
• VIN = 12V
• VOUT = 5V
• RL = 10
• Switching transistor Q1 is Toshiba 2SA1680 (IC,MAX = 2A, VCE,MAX = 50V )
• RB=390
3.1 Voltage and current stresses
• Simulation result shows the collector peak current at start-up transient. This peak
current is limited by the resistor RB. The current should not exceed the maximum
current rating of transistor Q1 (2SA1680 IC,MAX = 2A, VCE,MAX = 50V ).
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 13
Time
0s 2ms 4ms 6ms 8ms 10ms
1 V(Q1:e,Q1:c) 2 IE(Q1)
0V
10V
20V1
SEL>>
0A
1.0A
2.0A2
SEL>>
V(OUT+,OUT-)
0V
2.5V
5.0V
-VCE(t)
-IC(t)
Peak current
at start-up
VO(t)
Time
20.6us 21.0us 21.4us 21.8us 22.2us
1 -IB(Q1) 2 -IC(Q1)
0A
200mA
-100mA
1
>>
0A
2.0A
-1.0A
2
3.2 Transistor characteristics
VCE(sat)-IC characteristics Turn-off characteristics
• Losses in Q1 depend on the transistor characteristics. Conduction loss is depends on VCE (sat) – ICand switching loss is depends on Switching time characteristics ( turn-on and turn-off )
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 14
0.01
0.1
1
10
100
0.001 0.01 0.1 1
- IC(mA)
- V
CE
(SA
T)
(V)
Measurement
Simulation
tf
_90%
_10%
-IB(t)
-IC(t)
Time
9.954ms 9.958ms 9.962ms 9.966ms 9.970ms 9.974ms 9.978ms 9.982ms
1 V(Q1:e,Q1:c) 2 IE(Q1)
0V
4V
8V
12V
16V
20V1
0A
0.2A
0.4A
0.6A
0.8A
1.0A2
SEL>>SEL>>
W(Q1) AVG(W(Q1))
0W
1.0W
2.0W
3.0W
4.0W
5.0W
6.0W
7.0W
8.0W
3.3 Transistor Q1 losses
• Simulation results shows waveforms of IC and VCE of transistor Q1. Switching power
loss and average power loss are also shown.
Q1 Power Loss
Average Loss
-VCE(t)-IC(t)
Peak
magnitude
current
15All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
D1(SBD) trr
contribute
Switching
loss (turn-on)
Switching
loss (turn-off)
Conduction loss
(VCE(SAT) x IC)
Time
9.960ms 9.962ms 9.964ms
1 V(Q1:e,Q1:c) 2 IE(Q1)
0V
4V
8V
12V
16V
20V1
0A
200mA
400mA
2
SEL>>SEL>>
W(Q1) AVG(W(Q1))
0W
1.0W
2.0W
3.0W
4.0W
5.0W
6.0W
7.0W
8.0W
3.3 Transistor Q1 losses (zoomed)
• Simulation results shows the contribute of D1(SBD) recovery time trr ,that elevate
losses in the switch transistor Q1.
Q1 Power Loss
-VCE(t)
-IC(t)
16All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
Switching
loss (turn-on)
Average Loss
D1(SBD) trr
contribute
Lo
8RHB
0
Vcc
Vcc12Vdc
OUT+
Q1Q2SA1680
RB
390 RL10
Rsense
0.25
0
OUT-
0
R14500
U1UPC494 1 2 3 4 5 6 7 8
910
11
12
13
14
15
16
R13.9k
R25.1k
R35.1k
R45.1k
R5240k
R62.4k
R77.5k
0
0
VR11.45k
VR3
2k
0
0
C2
0.01uF
C3100nF
C410u
RV2-1{2k-R1}
0
RV2-2{R1}
0 0
R15100
R16100k
R13
7.5k R11500
C51000pFIC = 0
R815k
R171k
C7100n
PARAMETERS:
R1 = 0.1
C1
+
CoRJJ-35V221MG5-T20
IC = 0
D1
XBS104V14R_P
4. Freewheeling Diode D1 (SBD)
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 17
• VIN = 12V
• VOUT = 5V
• RL = 10
• Freewheeling diode D1 is Schottky Barrier Diode (SBD), XBS104V14R (IFSM=20A ,
VRM=40V) from Torex Semiconductor.
Time
0s 2ms 4ms 6ms 8ms 10ms
1 V(D1:2,D1:1) 2 I(D1)
10V
20V
-1V
1
SEL>>0A
1.0A
2.0A2
SEL>>
V(OUT+,OUT-)
0V
2.5V
5.0V
4.1 Voltage and current stresses
• Simulation result shows the forward peak current at start-up transient. The peak
current should not exceed the maximum current rating of shottky barrier diode D1
(XBS104V14R : IFSM=20A , VRM=40V).
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 18
VR(t)
IF(t)
Peak current
at start-up
VO(t)
4.2 Schottky barrier diode (SBD) characteristics
VR - IR characteristics CT - VR characteristics
• Losses in D1 depend on the SBD characteristics. Reverse leakage loss is depends on VR – IRcharacteristics and reverse recovery loss is depends on junction capacitance characteristics.
• Graphs show agreement between the simulations and measurements of SBD Professional model.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 19
0.001
0.010
0.100
1.000
10.000
0 10 20 30 40
Re
ve
rse
Cu
rre
nt:
IR (
mA
)
Reverse Voltage:VR (V)
Measurement
Simulation
0
100
200
300
400
500
5 15 25 35
Inte
r-T
erm
ina
l Ca
pa
cit
y:C
t (p
F)
Reverse Voltage:VR(V)
Measurement
Simulation
Time
9.955ms 9.960ms 9.965ms 9.970ms 9.975ms 9.980ms
1 V(D1:A,D1:C) 2 I(D1:A)
0V
-14V
14V1
0A
-0.6A
0.6A2
>>
W(D1) AVG(W(D1))
0W
200mW
400mW
SEL>>
4.3 Freewheeling diode D1 (SBD) losses
• Simulation results shows waveforms of IF and VAK of freewheel diode D1 ,which is a
Schottky type. Switching power loss and average power loss are also shown.
VAK(t)
IF(t)
20All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
Reverse recovery
characteristic
Conduction
loss
Reverse
recovery loss
D1 (SBD) Power Loss
Average Loss
Reverse
leakage loss
Time
9.9602ms 9.9604ms 9.9606ms 9.9608ms 9.9610ms 9.9612ms 9.9614ms 9.9616ms 9.9618ms 9.9620ms
1 V(D1:A,D1:K) 2 I(D1:A)
0V
-12V
12V1
0A
400mA
-200mA
2
>>
W(D1) AVG(W(D1))
0W
200mW
400mW
SEL>>
4.3 Freewheeling diode D1 (SBD) losses (Zoomed)
• Simulation results shows the reverse recovery time - trr of D1.
• Average loss in diode is 72.75mW
• Reverse leakage loss is approximately 907uW.
21All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
Average Loss = 72.75mW
Reverse Leakage Loss = 907uW
Reverse recovery
Reverse
recovery loss
Reverse
leakage loss
Time
9.9610ms 9.9612ms 9.9614ms 9.9616ms 9.9618ms 9.9620ms 9.9622ms 9.9624ms 9.9626ms 9.9628ms
1 V(D1:A,D1:C) 2 I(D1:A)
0V
-12V
12V1
SEL>>
0A
-200mA
400mA2
SEL>>
W(D1) AVG(W(D1))
0W
200mW
400mW
4.4 Schottky barrier diode Standard model
• VR – IR characteristics is not included in the Standard model.
• Average loss in diode is 72.4mW ( the Professional model result is 72.75mW )
• Reverse leakage loss is approximately 187uW (the Professional model result is
907uW).
22All Rights Reserved Copyright (C) Bee Technologies Corporation 2009
Reverse recovery
characteristic
Reverse
recovery loss
Reverse
leakage loss Average Loss = 72.4mW
Reverse Leakage Loss = 187uW
0
Vcc
Vcc12Vdc
OUT+
Q1Q2SA1680
RB
390 RL34
Rsense
0.25
0
OUT-
0
R14500
U1UPC494 1 2 3 4 5 6 7 8
910
11
12
13
14
15
16
R13.9k
R25.1k
R35.1k
R45.1k
R5240k
R62.4k
R77.5k
0
0
VR11.45k
VR3
2k
0
0
C2
0.01uF
C3100nF
C410u
RV2-1{2k-R1}
0
RV2-2{R1}
0 0
R15100
R16100k
R13
7.5k R11500
C51000pFIC = 0
R815k
R171k
C7100n
PARAMETERS:
R1 = 0.1
C1
+
CoRJJ-35V221MG5-T20
IC = 0
D1
XBS104V14R_P
Lo
{Lo}
1 2Rlo
0.63
PARAMETERS:
Lo = 300u
5. Output Inductor Value
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 23
• VIN = 12V
• VOUT = 5V
• RL=34 (IOUT 0.15A)
• Output inductor value Lo are 150uH and 300uH (Parametric sweep)
Time
9.90ms 9.91ms 9.92ms 9.93ms 9.94ms 9.95ms 9.96ms 9.97ms 9.98ms 9.99ms
I(Lo:1) I(RL)
0A
500mA
600mA
5. Output Inductor Value
• Simulation results shows the inductor current compare to minimum load current. If
0.5*IL,RIPPLE is less than IO,min, the inductor will operate in the “continuous” operating
mode (CCM)
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 24
Inductor current at
L=330uF, CCM,
f=38kHz
IL,RIPPLE
IO,min = 150mA
5. Output Inductor Value
The inductor value is calculate by.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 25
Where
• LCCM is output inductance that converter at load RL still working in CCM.
• RL is load resistance at the minimum output current, RL = VO / IO,min
• f is switching frequency
I
LOICCM
fV
RVVL
2
Which the IO,min is 150mA and VO is 5V, RL is approximately 34. At VIN=12V and f=38kHz ,this
equation calls for L 261uH.
The output inductor value is selected to set the ripple current. The too small value leads to
larger ripple current that will lead to more output ripple voltage due to the output capacitor ESR.
(3)
Time
9.83ms 9.84ms 9.85ms 9.86ms 9.87ms 9.88ms 9.89ms 9.90ms 9.91ms 9.92ms 9.93ms
I(Lo) I(RL)
0A
500mA
600mA
5. Output Inductor Value
• Simulation results shows that the inductor will operates in the “discontinuous”
operating mode (DCM), If reduce the inductance value to 150uH.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 26
I(LO) @ 300uH,
CCM
I(LO) @ 150uH,
DCM
_IO,min = 150mA
Lo
8RHB
Vcc
0
Vcc12Vdc
OUT+
Q1Q2SA1680
RB
390 RL10
Rsense
0.25
0
OUT-
0
R14500
U1UPC494 1 2 3 4 5 6 7 8
910
11
12
13
14
15
16
R13.9k
R25.1k
R35.1k
R45.1k
R5240k
R62.4k
R77.5k
0
0
VR11.45k
VR3
2k
0
0
C2
0.01uF
C3100nF
C410u
RV2-1{2k-R1}
0
RV2-2{R1}
0 0
R15100
R16100k
R13
7.5k R11500
C51000pFIC = 0
R815k
R171k
C7100n
PARAMETERS:
R1 = 0.1
C1
Co
{Co}
RESR
{ESR}
D1
DXBS104V14R
PARAMETERS:Co = 200uESR = 200m
6. Output Capacitor
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 27
• VIN = 12V
• VOUT = 5V
• RL=10
• Output capacitor value Co are 100uF and 200uF (Parametric sweep)
6. Output Capacitor
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 28
In addition, the voltage component due to the capacitor ESR must be considered, as
shown in equation (5).
Where
• IL,RIPPLE is an inductor ripple current.
• VO,RIPPLE is an output ripple voltage.
• f is switching frequency
RIIPLEO
RIPPLELO
Vf
IC
,
,min,
8
RIPPLEL
RIIPLEOESR
I
VR
,
,
• RESR VRIPPLE / IL,RIPPLE , At VRIPPLE =50mV and IL,RIPPLE =250mA , this equation calls for
RESR value less than 200m.
The minimum output capacitor is determined by the amount of inductor ripple current, and can
be calculated by the equation:
(4)
(5)
Time
0s 1.0ms 2.0ms 3.0ms 4.0ms 5.0ms
V(OUT+,OUT-)
0V
2.0V
3.0V
4.0V
5.0V
6.0V
SEL>>
Time
4.90ms 4.92ms 4.94ms 4.96ms 4.98ms 5.00ms
V(OUT+,OUT-)
5.0V
4.9V
6. Output Capacitor
• Overshoot voltage transient is also considered for output capacitor selection,
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 29
RJJ-35V221MG5-T20
(220uF electrolytic capacitor
with ESR=200m)
VO,RIPPLE (Zoomed)
100uF with ESR=200m
capacitor, overshoot voltage
is too big
Overshoot
CO=100uFCO=200uF
PARAMETERS:
C3 = 0.1u
Lo
8RHB
0
Vcc
Vcc12Vdc
OUT+
Q1Q2SA1680
RB
390 RL10
Rsense
0.25
0
OUT-
0
R14500
U1UPC494 1 2 3 4 5 6 7 8
910
11
12
13
14
15
16
R13.9k
R25.1k
R35.1k
R45.1k
R5240k
R62.4k
R77.5k
0
0
VR11.45k
VR3
2k
0
0
C2
0.01uF
C3{C3}
C410u
RV2-1{2k-R1}
0
RV2-2{R1}
0 0
R15100
R16100k
R13
7.5k R11500
C51000pFIC = 0
R815k
R171k
C7100n
PARAMETERS:
R1 = 0.1
C1
+
CoRJJ-35V221MG5-T20
IC = 0
D1
XBS104V14R_P
7. Voltage Control Feedback Loop
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 30
• VIN = 12V
• VOUT = 5V
• RL=10
• Capacitor C3 value are 0.01uF and 0.1uF (Parametric sweep)
Time
2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms
V(OUT+,OUT-)
4.5V
5.0V
5.5V
V(U1:3)
0V
1.0V
2.0V
SEL>>
7. Voltage Control Feedback Loop
• Simulation result shows the oscillation ripple that given from the feed back loop with
C3=0.01uF. This circuit calls for C3 more than 0.01uF to avoid oscillation, C3=0.1uF is
selected.
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 31
Oscillation
ripple!
C3 = 0.01uF
Feedback voltage:
V(IC pin3)
C3 = 0.1uF
C3 = 0.01uF
C3 = 0.1uF
Output voltage:
VO
Simulation Index
All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 32
Simulations Folder name
1. Transient simulation (@ VIN=12V, RL=10)......................................
2. Efficiency (@ VIN=12V, RL=10).........................................................
3. Step-load response (@ VIN=12V, IOUT=250mA / 500mA )...................
4. Power switch devices losses (Q1 and D1)..........................................
5. Output inductor....................................................................................
6. Output capacitor..................................................................................
7. Voltage control feedback loop.............................................................
Transient
Efficiency
Step-load
Losses
Lout
Cout
Feedback