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

2. Contents Slide # 1. Buck Converter using PC494: VIN=12V, VOUT=5V@0.5A..................................................................... 3 1.1 Output voltage................................................................................................................................... 4 1.2 Output current................................................................................................................................... 5 1.3 Output ripple voltage ........................................................................................................................ 6 1.4 Efficiency…….................................................................................................................................... 7 1.5 Step-load response........................................................................................................................... 8 2. Basic Operation....................................................................................................................................... 9 2.1 Output voltage equations.................................................................................................................. 10 2.2 Basic operation waveforms............................................................................................................... 11 3. Switching Transistor Q1.......................................................................................................................... 12 3.1 Voltage and current stresses............................................................................................................ 13 3.2 Transistor characteristics.................................................................................................................. 14 3.3 Transistor Q1 losses ........................................................................................................................ 15-16 4. Freewheeling Diode D1 (SBD)……………………………....................................................................... 17 4.1 Voltage and current stresses............................................................................................................ 18 4.2 Schottky barrier diode (SBD) characteristics.................................................................................... 19 4.3 Freewheeling diode D1 (SBD) losses............................................................................................... 20-21 4.4 Schottky barrier diode Standard model……..................................................................................... 22 5. Output Inductor Value.............................................................................................................................. 23-26 6. Output Capacitor..................................................................................................................................... 27-29 7. Voltage Control Feedback Loop.............................................................................................................. 30-31 Simulations index.......................................................................................................................................... 32 All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 2

3. 1. Buck Converter using PC494: VIN=12V, VOUT=5V@0.5A Vcc Lo OUT+ 8RHB Vcc R13 VR3 Q1 12Vdc Q2SA1680 D1 + 500 XBS104V14R_P 0 R14 7.5k 2k R11 RB IC = 0 500 390 Co RL R15 RJJ-35V221MG5-T20 10 100 C1 0.01uF C2 Rsense OUT- R17 16 15 14 13 12 11 10 9 0 0.25 R1 1k R16 3.9k R3 100k 0 5.1k C7 U1 0 1 2 3 4 5 6 7 8 VR1 100n UPC494 1.45k R5 0 240k RV2-2 R2 R4 C3 R6 {R1} C5 R8 5.1k 5.1k 100nF 2.4k 1000pF 15k IC = 0 RV2-1 0 0 0 0 0 {2k-R1} C4 PARAMETERS: 10u R1 = 0.1 R7 7.5k • 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  Schottky barrier diode (SBD) D1 is simulated using a Professional model. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 3

4. 1.1 Output voltage 6.0V Overshoot voltage 5.0V 4.0V 3.0V 2.0V 1.0V Time to reach steady state 0V 0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10ms V(OUT+,OUT-) Time • The output voltage is regulated at 5V (RL=10) ,voltage overshoot at startup is 0.6V. Steady state is reached within 4ms. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 4

5. 1.2 Output current 600mA Overshoot current 500mA 400mA 300mA 200mA 100mA Time to reach steady state 0A 0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10ms I(RL) Time • The output current is 0.5A (RL=10) ,current overshoot at startup is 60mA. Steady state is reached within 4ms. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 5

6. 1.3 Output ripple voltage 5.12V 5.08V 5.04V 5.00V 4.96V Output voltage ripple 4.92V 4.88V 4.84V 4.80V 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-) Time • The output ripple voltage is less than 1% of the output voltage ( < 50 mVP-P ). All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 6

7. 1.4 Efficiency 100 90 80 Efficiency = > 74% 70 60 50 40 30 20 10 0 5ms 6ms 7ms 8ms 9ms 10ms 100*AVG(V(RL:1)*I(RL))/AVG(-I(V1)*V(V1:+)) Time • 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

8. 1.5 Step-load response 750mA 500mA 250mA / 500mA step-load 250mA 0A I(IL) 5.5V 250mV 5.0V -250mV SEL>> 4.5V 5ms 6ms 8ms 10ms 12ms 14ms 16ms 18ms 20ms V(OUT+,OUT-) Time • Simulation results shows the transient responses, when load current steps up and steps down. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 8

9. 2. Basic Operation V in Vcc VO -IC(Q1) L1 I(L1) Q1 1 2 OUT+ I(D1) D1 C1 R1 Rload Vcc R2 OUT- Error Amp 0 + PWM Control PWM output pulse Circuit - Vref 2.5V 0 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. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 9

10. 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.  R1  R 2  VOUT     Vref (1)  R2  • If the circuit works in continuous conduction mode (CCM) , output voltage and TON follow the equation below.  TON  VOUT     Vin (2)  T  All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 10

11. 2.2 Basic operation waveforms 14V Vin TON 0V V(Q1:c) T -IC(Q1) 500mA SEL>> 0A IE(Q1) 500mA I(D1) 0A I(D1)  VCC  VΟ   VΟ  0.7A ΔΙ     ΤΟΝ ΔΙ     ΤΟFF I(L1)  L1   L1  I(RL)=VO/Rload / I(RL) 0.3A 7.81ms 7.82ms 7.84ms 7.86ms 7.88ms 7.90ms 7.91ms I(Lo:1) I(RL) Time • Simulation result shows the waveforms and magnitude of the current throughout the circuit. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 11

12. 3. Switching Transistor Q1 Vcc Lo OUT+ 8RHB Vcc R13 VR3 Q1 12Vdc Q2SA1680 D1 + 500 XBS104V14R_P 0 R14 7.5k 2k R11 RB IC = 0 500 390 Co RL R15 RJJ-35V221MG5-T20 10 100 C1 0.01uF C2 Rsense OUT- R17 16 15 14 13 12 11 10 9 0 0.25 R1 1k R16 3.9k R3 100k 0 5.1k C7 U1 0 1 2 3 4 5 6 7 8 VR1 100n UPC494 1.45k R5 0 240k RV2-2 R2 R4 C3 R6 {R1} C5 R8 5.1k 5.1k 100nF 2.4k 1000pF 15k IC = 0 RV2-1 0 0 0 0 0 {2k-R1} C4 PARAMETERS: 10u R1 = 0.1 R7 7.5k • VIN = 12V • VOUT = 5V • RL = 10 • Switching transistor Q1 is Toshiba 2SA1680 (IC,MAX = 2A, VCE,MAX = 50V ) • RB=390  All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 12

13. 3.1 Voltage and current stresses 5.0V VO(t) 2.5V 0V V(OUT+,OUT-) 20V 2.0A Peak current 1 2 at start-up 10V 1.0A -VCE(t) SEL>> -IC(t) 0V 0A 0s 2ms 4ms 6ms 8ms 10ms 1 V(Q1:e,Q1:c) 2 IE(Q1) Time • 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

14. 3.2 Transistor characteristics VCE(sat)-IC characteristics Turn-off characteristics 100 200mA 2.0A Measurement 1 2 Simulation 10 -IC(t) _90% - VCE(SAT) (V) -IB(t) 1 tf _10% 0A 0A 0.1 >> 0.01 -100mA -1.0A 20.6us 21.0us 21.4us 21.8us 22.2us 0.001 0.01 0.1 1 1 -IB(Q1) 2 -IC(Q1) - IC(mA) Time • Losses in Q1 depend on the transistor characteristics. Conduction loss is depends on VCE (sat) – IC and switching loss is depends on Switching time characteristics ( turn-on and turn-off ) All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 14

15. 3.3 Transistor Q1 losses 8.0W 7.0W Q1 Power Loss 6.0W Switching loss (turn-on) 5.0W Switching 4.0W loss (turn-off) 3.0W Conduction loss 2.0W Average Loss (VCE(SAT) x IC) 1.0W 0W W(Q1) AVG(W(Q1)) 20V 1.0A 1 2 Peak 16V 0.8A D1(SBD) trr magnitude -VCE(t) contribute current 12V 0.6A -IC(t) 8V 0.4A 4V 0.2A SEL>> 0V 0A 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) Time • Simulation results shows waveforms of IC and VCE of transistor Q1. Switching power loss and average power loss are also shown. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 15

16. 3.3 Transistor Q1 losses (zoomed) 8.0W 7.0W Q1 Power Loss 6.0W 5.0W Switching 4.0W loss (turn-on) 3.0W 2.0W Average Loss 1.0W 0W W(Q1) AVG(W(Q1)) 20V 1 2 -IC(t) 16V 400mA -VCE(t) 12V D1(SBD) trr contribute 8V 200mA 4V SEL>> 0V 0A 9.960ms 9.962ms 9.964ms 1 V(Q1:e,Q1:c) 2 IE(Q1) Time • Simulation results shows the contribute of D1(SBD) recovery time trr ,that elevate losses in the switch transistor Q1. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 16

17. 4. Freewheeling Diode D1 (SBD) Vcc Lo OUT+ 8RHB Vcc R13 VR3 Q1 12Vdc Q2SA1680 D1 + 500 XBS104V14R_P 0 R14 7.5k 2k R11 RB IC = 0 500 390 Co RL R15 RJJ-35V221MG5-T20 10 100 C1 0.01uF C2 Rsense OUT- R17 16 15 14 13 12 11 10 9 0 0.25 R1 1k R16 3.9k R3 100k 0 5.1k C7 U1 0 1 2 3 4 5 6 7 8 VR1 100n UPC494 1.45k R5 0 240k RV2-2 R2 R4 C3 R6 {R1} C5 R8 5.1k 5.1k 100nF 2.4k 1000pF 15k IC = 0 RV2-1 0 0 0 0 0 {2k-R1} C4 PARAMETERS: 10u R1 = 0.1 R7 7.5k • VIN = 12V • VOUT = 5V • RL = 10 • Freewheeling diode D1 is Schottky Barrier Diode (SBD), XBS104V14R (IFSM=20A , VRM=40V) from Torex Semiconductor. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 17

18. 4.1 Voltage and current stresses 5.0V VO(t) 2.5V 0V V(OUT+,OUT-) 20V 2.0A Peak current 1 2 at start-up 10V 1.0A VR(t) SEL>> IF(t) 0A -1V 0s 2ms 4ms 6ms 8ms 10ms 1 V(D1:2,D1:1) 2 I(D1) Time • 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

19. 4.2 Schottky barrier diode (SBD) characteristics VR - IR characteristics CT - VR characteristics 10.000 500 Measurement Measurement Simulation Simulation Inter-Terminal Capacity:Ct (pF) 400 1.000 Reverse Current:IR (mA) 300 0.100 200 0.010 100 0.001 0 0 10 20 30 40 5 15 25 35 Reverse Voltage:VR (V) Reverse Voltage:VR(V) • Losses in D1 depend on the SBD characteristics. Reverse leakage loss is depends on VR – IR characteristics 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

20. 4.3 Freewheeling diode D1 (SBD) losses 400mW Reverse Conduction recovery loss loss 200mW D1 (SBD) Power Loss Reverse leakage loss 0W SEL>> Average Loss W(D1) AVG(W(D1)) 14V 0.6A 1 2 IF(t) Reverse recovery characteristic VAK(t) 0V 0A >> -14V -0.6A 9.955ms 9.960ms 9.965ms 9.970ms 9.975ms 9.980ms 1 V(D1:A,D1:C) 2 I(D1:A) Time • 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. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 20

21. 4.3 Freewheeling diode D1 (SBD) losses (Zoomed) 400mW Reverse recovery loss 200mW Reverse leakage loss Average Loss = 72.75mW 0W Reverse Leakage Loss = 907uW SEL>> W(D1) AVG(W(D1)) 12V 400mA 1 2 Reverse recovery 0V 0A >> -12V -200mA 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) Time • Simulation results shows the reverse recovery time - trr of D1. • Average loss in diode is 72.75mW • Reverse leakage loss is approximately 907uW. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 21

22. 4.4 Schottky barrier diode Standard model 400mW Reverse recovery loss 200mW Reverse leakage loss Average Loss = 72.4mW 0W Reverse Leakage Loss = 187uW W(D1) AVG(W(D1)) 12V 400mA 1 2 Reverse recovery characteristic 0V 0A SEL>> -12V -200mA 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) Time • 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). All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 22

23. 5. Output Inductor Value PARAMETERS: Lo = 300u Vcc Lo Rlo 1 2 OUT+ {Lo} 0.63 Vcc R13 VR3 Q1 12Vdc Q2SA1680 D1 + 500 XBS104V14R_P 0 R14 7.5k 2k R11 RB IC = 0 500 390 Co RL R15 RJJ-35V221MG5-T20 34 100 C1 0.01uF C2 Rsense OUT- R17 16 15 14 13 12 11 10 9 0 0.25 R1 1k R16 3.9k R3 100k 0 5.1k C7 U1 0 1 2 3 4 5 6 7 8 VR1 100n UPC494 1.45k R5 0 240k RV2-2 R2 R4 C3 R6 {R1} C5 R8 5.1k 5.1k 100nF 2.4k 1000pF 15k IC = 0 RV2-1 0 0 0 0 0 {2k-R1} C4 PARAMETERS: 10u R1 = 0.1 R7 7.5k • VIN = 12V • VOUT = 5V • RL=34 (IOUT  0.15A) • Output inductor value Lo are 150uH and 300uH (Parametric sweep) All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 23

24. 5. Output Inductor Value 600mA 500mA Inductor current at L=330uF, CCM, f=38kHz IO,min = 150mA IL,RIPPLE 0A 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) Time • 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

25. 5. Output Inductor Value 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. The inductor value is calculate by. LCCM  VI  VO  RL (3) 2 fVI 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 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. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 25

26. 5. Output Inductor Value 600mA 500mA I(LO) @ 300uH, CCM _IO,min = 150mA 0A 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) Time I(LO) @ 150uH, DCM • 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

27. 6. Output Capacitor PARAMETERS: Co = 200u Vcc Lo ESR = 200m OUT+ 8RHB Vcc R13 VR3 Q1 12Vdc Q2SA1680 D1 Co 500 DXBS104V14R {Co} 0 R14 7.5k 2k R11 RB 500 390 RL R15 RESR 10 100 C1 {ESR} 0.01uF C2 Rsense OUT- R17 9 16 15 14 13 12 11 10 0 0.25 R1 1k R16 3.9k R3 100k 0 5.1k C7 U1 0 1 2 3 4 5 6 7 8 VR1 100n UPC494 1.45k R5 0 240k RV2-2 R2 R4 C3 R6 {R1} C5 R8 5.1k 5.1k 100nF 2.4k 1000pF 15k IC = 0 RV2-1 0 0 0 0 0 {2k-R1} C4 PARAMETERS: 10u R1 = 0.1 R7 7.5k • VIN = 12V • VOUT = 5V • RL=10 • Output capacitor value Co are 100uF and 200uF (Parametric sweep) All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 27

28. 6. Output Capacitor The minimum output capacitor is determined by the amount of inductor ripple current, and can be calculated by the equation: IL , RIPPLE CO , min  (4) 8  f  VO , RIIPLE Where • IL,RIPPLE is an inductor ripple current. • VO,RIPPLE is an output ripple voltage. • f is switching frequency In addition, the voltage component due to the capacitor ESR must be considered, as shown in equation (5). VO, RIIPLE RESR  (5) IL, RIPPLE • RESR  VRIPPLE / IL,RIPPLE , At VRIPPLE =50mV and IL,RIPPLE =250mA , this equation calls for RESR value less than 200m. All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 28

29. 6. Output Capacitor 5.0V CO=100uF CO=200uF VO,RIPPLE (Zoomed) 4.9V 100uF with 4.90ms ESR=200m RJJ-35V221MG5-T20 4.92ms 4.94ms 4.96ms 4.98ms 5.00ms capacitor, overshoot V(OUT+,OUT-) voltage (220uF electrolytic capacitor is too big with ESR=200m) Time 6.0V Overshoot 5.0V 4.0V 3.0V 2.0V SEL>> 0V 0s 1.0ms 2.0ms 3.0ms 4.0ms 5.0ms V(OUT+,OUT-) Time • Overshoot voltage transient is also considered for output capacitor selection, All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 29

30. 7. Voltage Control Feedback Loop Vcc Lo OUT+ 8RHB Vcc R13 VR3 Q1 12Vdc Q2SA1680 D1 + 500 XBS104V14R_P 0 R14 7.5k 2k R11 RB IC = 0 500 390 Co RL R15 RJJ-35V221MG5-T20 10 100 C1 0.01uF C2 Rsense OUT- R17 16 15 14 13 12 11 10 9 0 0.25 R1 1k R16 3.9k R3 100k 0 5.1k C7 U1 0 1 2 3 4 5 6 7 8 VR1 100n UPC494 1.45k R5 0 240k RV2-2 R2 R4 C3 R6 {R1} C5 R8 5.1k 5.1k {C3} 2.4k 1000pF 15k IC = 0 PARAMETERS: RV2-1 0 0 0 0 0 C3 = 0.1u {2k-R1} C4 PARAMETERS: 10u R1 = 0.1 R7 7.5k • VIN = 12V • VOUT = 5V • RL=10 • Capacitor C3 value are 0.01uF and 0.1uF (Parametric sweep) All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 30

31. 7. Voltage Control Feedback Loop 2.0V Feedback voltage: V(IC pin3) C3 = 0.01uF C3 = 0.1uF 1.0V SEL>> 0V V(U1:3) 5.5V Output voltage: VO C3 = 0.01uF C3 = 0.1uF 5.0V Oscillation ripple! 4.5V 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms V(OUT+,OUT-) Time • 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

32. Simulation Index Simulations Folder name 1. Transient simulation (@ VIN=12V, RL=10)...................................... Transient 2. Efficiency (@ VIN=12V, RL=10)......................................................... Efficiency 3. Step-load response (@ VIN=12V, IOUT=250mA / 500mA )................... Step-load 4. Power switch devices losses (Q1 and D1).......................................... Losses 5. Output inductor.................................................................................... Lout 6. Output capacitor.................................................................................. Cout 7. Voltage control feedback loop............................................................. Feedback All Rights Reserved Copyright (C) Bee Technologies Corporation 2009 32

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

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

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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