PWM Step-down Converter(NJM2309)

1,710 views
1,622 views

Published on

PWM Step-down Converter(NJM2309). Concept kit provided by Bee Technologies.

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,710
On SlideShare
0
From Embeds
0
Number of Embeds
52
Actions
Shares
0
Downloads
44
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

PWM Step-down Converter(NJM2309)

  1. 1. Case Study:NJM2309 Application Circuit Design (PWM Step-down Converter)<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />1<br />
  2. 2. Contents<br />Design Specification<br />NJM2309 Typical Application Circuit<br />Averaged Buck Switch Model<br />Buck Regulator Design Workflow<br />Setting PWM Controller’s Parameters.<br />Programming Output Voltage: Rupper, Rlower<br />Inductor Selection: L<br />Capacitor Selection: C, ESR<br />Stabilizing the Converter<br />Load Transient Response Simulation<br /><ul><li>Reference: Load Transient Response Simulation with PWM IC Transient Model</li></ul>Appendix<br />Type 2 Compensation Calculation using Excel<br />Feedback Loop Compensators<br />Simulation Index<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />2<br />
  3. 3. Design Specification<br />Step-Down (Buck) Converter :<br /><ul><li>VIN, MAX = 32 (V)
  4. 4. VIN, MIN = 6 (V)
  5. 5. VOUT = 3.3 (V)
  6. 6. VOUT, Ripple = 1% ( 33mVP-P )
  7. 7. IOUT, MAX = 1.0 (A)
  8. 8. IOUT, MIN = 0.2 (A)</li></ul>Control IC :<br /><ul><li>NJM2309 (Switching Regulator Control IC for Step-Down)
  9. 9. Switching Frequency – fosc = 105 (kHz)</li></ul>All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />3<br />NJM2309 Datasheet<br />
  10. 10. NJM2309 Typical Application Circuit<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />4<br />Power Switches<br />Filter & Load<br />PWM Controller<br /> Schematic is captured from NJM2309 datasheet page 4.<br />
  11. 11. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />5<br />TASK: Design and Evaluation of the Circuit <br />3?<br />2?<br />1<br />4?<br />5?<br />NJM2309 Typical Application Circuit<br />
  12. 12. Buck Regulator Design Workflow <br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />6<br />Setting PWM Controller’s Parameters: VREF, VP<br />1<br />Setting Output Voltage: Rupper, Rlower<br />2<br />Inductor Selection: L<br />3<br />Capacitor Selection: C, ESR<br />4<br />Stabilizing the Converter: R2, C1, C2<br /><ul><li>Step1: Open the loopwith LoL=1kH and CoL=1kF then inject an AC signal to generate Bode plot. (always default)
  13. 13. Step2: Set C1=1kF, C2=1fF, (always keep the default value) and R2= calculated value (Rupper//Rlower) as the initial values.
  14. 14. Step3: Select a crossover frequency (about 10kHz or fc < fosc/4). Then complete the table.
  15. 15. Step4: Read the Gain and Phase value at the crossover frequency (10kHz) from the Bode plot, Then put the values to the table
  16. 16. Step5: Select the phase margin at the fc ( > 45 ). Then change the K value until it gives the satisfied phase margin, for this example K=6 is chosen for Phase margin = 46.
  17. 17. Remark: If K-factor fail to gives the satisfied phase margin, Increase the output capacitor C then try Step1 to Step5 again.</li></ul>5<br />Load Transient Response Simulation<br />6<br />
  18. 18. Buck Regulator Design Workflow <br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />7<br />3<br />4<br />5<br />2<br />1<br />
  19. 19. <ul><li>VREF = VB = 0.52 (V)
  20. 20. VP=2.5 (vFBH and vFBLare not provided, the default value is used).</li></ul>Setting PWM Controller’s Parameters<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />8<br />1<br /><ul><li> Table is captured from NJM2309 datasheet page 2.</li></li></ul><li>Use the following formula to select the resistor values.<br /><ul><li>Rlower can be between 1k and 5k.</li></ul>Given: VOUT = 3.3V<br /> VREF = 0.52V<br /> Rlower = 1k<br />then:  Rupper = 5.346k<br />Setting Output Voltage: Rupper, Rlower<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />9<br />2<br />
  21. 21. Inductor Selection: L<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />10<br />Inductor Value<br />from<br />Given: <br />VI,max = 40(V), VOUT = 3.3(V)<br />IOUT,min = 0.2(A)<br />RL,min = (VOUT /IOUT,min ) = 16.5()<br />fosc = 105(kHz)<br />Then:<br />LCCM 72.1(uH), <br /><ul><li>L = 100(uH) is selected</li></ul>3<br />
  22. 22. Capacitor Selection: C, ESR (NJM2309)<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />11<br />Capacitor Value<br />From<br />and<br />Given:<br />VI, max = 40 V<br />VOUT = 3.3 V, VOUT, Ripple = 1% ( 33mVP-P )<br />L (H) = 100<br />IOUT, MAX = 1(A), IL, Ripple = 0.25(A)<br />Then:<br /><ul><li>C 944 (F), C = 1000(F) is selected</li></ul>In addition:<br /><ul><li>ESR 132m</li></ul>4<br />
  23. 23. Stabilizing the Converter (NJM2309)<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />12<br />5<br />Specification:<br />VOUT = 3.3V<br />VIN = 6 ~ 32V<br />ILOAD = 0.2 ~ 1A<br />PWM Controller:<br />VREF = 0.52V<br />VP = 2.5V<br />fOSC = 105kHz<br />Rlower = 1k,<br />Rupper = 5.346k,<br />L = 100uH, <br />C = 1000uF (ESR = 132m)<br />Task:<br /><ul><li>to find out the element of the Type 2 compensator ( R2, C1, and C2 )</li></ul>G(s)<br />1<br />e.g. Given values from National Semiconductor Corp. IC: LM2575 <br />2<br />3<br />4<br />
  24. 24. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />13<br />Stabilizing the Converter (NJM2309)<br />5<br />The element of the Type 2 compensator ( R2, C1, and C2 ), that stabilize the converter, can be extracted by using Type 2 Compensator Calculator (Excel sheet) and open-loop simulation with the Average Switch Models (ac models).<br />Step2 Set C1=1kF, C2=1fF, and R2=calculated value (Rupper//Rlower) as the initial values.<br />Step1 Open the loop with LoL=1kH and CoL=1kF then inject an AC signal to generate Bode plot.<br /> C1=1kF is AC shorted, and C2 1fF is AC opened (or Error-Amp without compensator).<br />
  25. 25. Stabilizing the Converter (NJM2309)<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />14<br />5<br />Step3 Select a crossover frequency (about 10kHz or fc < fosc/4 ), for this example, 10kHz is selected. Then complete the table.<br />values from <br />2<br />Calculated value of the Rupper//Rlower<br />values from <br />1<br />
  26. 26. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />15<br />Stabilizing the Converter (NJM2309)<br />5<br />Gain: T(s) = H(s)GPWM<br />Step4 Read the Gain and Phase value at the crossover frequency(10kHz) from the Bode plot, Then put the values to the table.<br />Phase  atfc<br />Tip: To bring cursor to the fc = 10kHz type “ sfxv(10k) ” in Search Command.<br />Cursor Search<br />
  27. 27. Stabilizing the Converter (NJM2309)<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />16<br />5<br />Step5 Select the phase margin at fc (> 45 ). Then change the K value (start from K=2) until it gives the satisfied phase margin, for this example K=3 is chosen for Phase margin = 48.<br />As the result; R2, C1, and C2 are calculated.<br />Remark: If K-factor fail to gives the satisfied phase margin, Increase the output capacitor C then try Step1 to Step5 again.<br /> K Factor enable the circuit designer to choose a loop cross-over frequency and phase margin, and then determine the necessary component values to achieve these results. A very big K value (e.g. K > 100) acts like no compensator (C1 is shorted and C2 is opened).<br />
  28. 28. Stabilizing the Converter (NJM2309)<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />17<br />5<br />The element of the Type 2 compensator ( R2, C1, and C2 ) extraction can be completed by Type 2 Compensator Calculator (Excel sheet) with the converter average models (ac models) and open-loop simulation.<br />The calculated values of the type 2 elements are:<br /><ul><li>R2=54.655k,
  29. 29. C1=0.874nF ,
  30. 30. C2=97.07pF.</li></ul>*Analysis directives: <br />.AC DEC 100 0.1 10MEG<br />
  31. 31. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />18<br />Stabilizing the Converter (NJM2309)<br />5<br />Gain and Phase responses after stabilizing<br />Gain: T(s) = H(s) G(s)GPWM<br />Phase  atfc<br />Phase margin = 48.801 at the cross-over frequency - fc = 9.237kHz.<br />Tip: To bring cursor to the cross-over point (gain = 0dB) type “ sfle(0) ” in Search Command.<br />Cursor Search<br />
  32. 32. Load Transient Response Simulation<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />19<br />The converter, that have been stabilized, are connected with step-load to perform load transient response simulation.<br />3<br />4<br />5<br />3.3V/16.5 = 0.2A step to 0.2+0.8=1.0A load<br />2<br />*Analysis directives: <br />.TRAN 0 20ms 0 1u<br />1<br />
  33. 33. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />20<br />Load Transient Response Simulation<br />Simulation<br />Output Voltage Change<br />Load Current<br /><ul><li>The simulation results illustrates the transient response of the converter with the stepping load .2A to 1A.</li></li></ul><li>Reference: Load Transient Response Simulation with PWM IC Transient Model<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />21<br />After the converter have been designed, the PWM IC Transient Model could be applied for more realistic simulation.<br />3<br />4<br />5<br />3.3V/16.5 = 0.2A step to 0.2+0.8=1.0A load<br />2<br />*Analysis directives: <br />.TRAN 0 12ms 0 200n SKIPBP<br />1<br /> Remark: PWM IC Transient Model and Simulations are not included with this package.<br />
  34. 34. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />22<br />Reference: Load Transient Response Simulation with PWM IC Transient Model<br />Simulation<br />Output Voltage Change<br />Load Current<br /><ul><li>The PWM IC Transient Model enables The VOUT, RIPPLE and others switching characteristics to be included in the simulation.</li></ul> Remark: PWM IC Transient Model and Simulations are not included with this package.<br />
  35. 35. A. Type 2 Compensation Calculation using Excel<br />All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />23<br />
  36. 36. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />24<br />B. Feedback Loop Compensators<br />Type1 Compensator<br />Type2 Compensator<br />Type2a Compensator<br />Type2b Compensator<br />Type3 Compensator<br />
  37. 37. All Rights Reserved Copyright (C) Bee Technologies Corporation 2011<br />25<br />C. Simulation Index<br />Libraries :<br />..bucksw.lib<br />..pwm_ctr.lib<br />Tool :<br /><ul><li>Type 2 Compensator Calculator (Excel sheet)</li>

×