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Concept kit:PWM Buck Converter Average Model (NJM2309)

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Concept kit:PWM Buck Converter Average Model (NJM2309)

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Concept kit:PWM Buck Converter Average Model (NJM2309)

  1. 1. :1’. Bee Ii‘: mmmmmm gles PWM Controller Power Switches Filter & Load (Voltage Mode Control) U? ., I: B K W L VOUT j. ' T. .4/vwvx E Q ~ ‘I T C Rot: } ESR ‘ I NJM2309 Application Circuit Design (PWM Step—down Converter)
  2. 2. Contents '«: ~'! §?. § - Design Specification - NJM2309 Typical Application Circuit - Averaged Buck Switch Model - Buck Regulator Design Workflow 1. Setting PWM Controller's Parameters. 2. Programming Output Voltage: Rupper, Rlower 3. Inductor Selection: L 4. Capacitor Selection: C, ESR 5. Stabilizing the Converter - Load Transient Response Simulation Reference: Load Transient Response Simulation with PWM IC Transient Model Appendix A. Type 2 Compensation Calculation using Excel B. Feedback Loop Compensators C. Simulation Index
  3. 3. Design Specification Step-Down (Buck) Converter : ' V| N,MAX = 32 (V) ' V| N,M| N = 6 (V) - VOUT = 3.3 (V) ' VOUT, Ripple = 1% ( 33mVP-P ) ' IOUT, MAX = 1-0 (A) ' IOUT, MIN = 0-2 (A) Control IC : NJM2309 Datasheet E NJM2309 switching Regulator Control IC for Step-Down n<iFM= RA1[>€. (. R|"Ti>N i= AI KAuFIJlI’Llr£ The Mmrmcn I} 4 sky slmvn Swim: g m, ..r. .r. : D: m. . wit‘ rte-r. Irg'. r-lmyr I fcar. ,rc<. an «arm carer: 11m if. ‘ or (mt-Juv: ‘ ; _~‘. _i -' _ G; ye: --xw avucaocns mm: 54.1! mm rumui am Mr: .m. '. ru. i.u' I41 sIu' “mm” “ii ulunl zxma hm Jr! mmm lE'2|ll‘I; "ll -nun! rnvprru--R ‘ J M11! .1 l-All nun o l>'. '4lI am Nu I mum nI'ullV1l‘u‘. Hl| l)I HT. ’ v- 12‘: 0 Wm : :4 mm warm ‘mg um rm 1-H. - olnlvtvth Ira. » rm‘. n-ill Wfllilullxll o rm-u I Minna Nlxm numlvuu-m~ o I lulu mm; .II- mm. :| l'u‘ll r; -loqnuu rm: -at-m om my-I unn- ‘&I| .l. ‘IlM. I Mil->1 ‘1|M, ’|(H HI'fl ‘JIM. ’ Nu. ‘ xx: l'N - NJM2309 (Switching Regulator Control IC for Step-Down) - Switching Frequency —fosc = 105 (kHz)
  4. 4. NJM2309 Typical Application Circuit -3%: -es. <2 Power Switches Filter & Load PWM Controller X Schematic is captured from NJM2309 datasheet page 4.
  5. 5. NJM2309 Typical Application Circuit eéeaaes TASK: Design and Evaluation of the Circuit V‘
  6. 6. Buck Regulator Design Workf| o_lv_ 7§~'§§£ 0 Setting PWM Controller's Parameters: VREF, VP 9 Setting Output Voltage: Rupper, Rlower O Inductor Selection: L 0 Capacitor Selection: C, ESR C Stabilizing the Converter: B2, C1, C2 ' Step1: Open the loop with LoL=1kH and CoL=1kF then inject an ACsignal to generate Bode plot. (always default) ' Step2: Set C1=1l(F, C2=1fF, (always keep the default value) and R2: calculated value (Rupper/ /Rlower) as the initial values. ' StQ3.' Select a crossover frequency (about 10kHz or fc <fosc/4). Then complete the table. - Stgzi: Read the Gain and Phase value at the crossover trguengy (10kHz) from the Bode plot, Then put the values to the table ' StQ5: Select the phase margin at thefc (> 45 "). Then change the K value until it gives the satisfied phase margin, for this example K=6 is chosenfor Phase margin = 46 ". ' Remark: If K-factor fail to gives the satisfied phase margin, Increase the output capacitor C then try Step1 to Step5 again. 0 Load Transient Response Simulation
  7. 7. '4' Buck Regulator Desigri1lVor}<flQw‘ -3:» 99.. .‘-‘E2 VREF = 1.23 ' 0
  8. 8. la Bee Setting PWM Controller's Parameters 4* v~= ~~»~«~= ERROR AMPLIFIER BLOCK PARAMETER svmso UNIT Reference Voltage V5 0 Si 0 52 O 53 V Open Loop Gain A, » 90 dB Maximum Outvutvoltage jj V <FBPin> j} "W Output Source Current mm “A Table is captured from NJM2309 datasheet page 2. ~/ VREF = VB = 0.52 (v) / VP=2.5 (V, _-BH and VFBL are not provided, the default value is used).
  9. 9. Setting Output Voltage: Rupper, Rlower I .31. Bee Yechnologles - Use the following formula to select the resistor values. VOUT = VREF 1+ Rapper Rlower - Rmwe, can be between 1k and 5k. Given: VOUT = 3.3V VREF = 0. 52v / Rlower = “(I2 then: /nuppe, = 5. 346k. (2
  10. 10. . ; ~'r. Bee 9 Inductor Selection: L I? ‘ v-mm 1 L V0 Inductor Value C from _ R ‘ - T mead LCCM Z (V1.max V0uT)>< L min ESR 2fi). v(‘VI. max ‘ Given: ' VI, max = 40(V)a VouT= 3-3(V) . lOUT. min = . RL, min = (VOUT/ lOUT, min) = - f0sC=105(kHz) Then: - LCCMZ 72.1(uH), / L = 100(uH) is selected
  11. 11. 0 Capacitor Selection: C, ESR (NJM2309) Vo Rload Capacitor Value From V]. max V01/T - L( V0. RIPPLE C 2 7,785 x (,5) and ESR S Given: IL. RIPPLE ~ V], max = 40 v ' Vour = 3-3 V- Vour, Ripple = 1% ( 33mVP-P ) - L (, uH) = 100 ' IOUT, MAX = 1(A)- IL, Ripple = 0-25(A) Then: / C2 944 um), C = 1000(/1F) is selected In addition: / ESR 5 132m! )
  12. 12. 6 Stabilizing the Converter (NJM2309) -«. ~'§. ?.§ Specification: 2 . . L VOUT = 3.3v ' V. N = 6 ~ 32V ILOAD = "' PWM nr ll r: VREF = O.52V VP = 2.5V . rose =105kHz e. g. Given values from National Sim ck: s¢n. ~;con4uctar. carn- K L. -"7 e —. .i )l L = 100UH, ' 5 C = 1000uF (ESR = 132mQ) 0 co; :1” ‘K VP=2.5 Task’. W va vnss = o.52 0 - to find out the element of the °"°°_L Type 2 compensator ( R2, C1, :0 and C2 )
  13. 13. 23¢ Bee Stabilizing the Converter (Nfl/ I2309) 4* v~= ~»~»= '=~ 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). U2 L : . . V: Rload 3.3 $teQ2 Set C1=1kE C2=1fI-', and R2=caIcuIated value $£’g1_ Open the loop with (Rupper/ /Rlower) as the LoL=1kH and CoL=1kF then inject _ initial values. on AC signal to generate Bode plot. % Rm, 5.34GK I U Rlflwt. 21‘? T ‘* _l_ VP = 2.5 7: V3 VREF = 0.52 0 at C1=1kF is AC shorted, and C2 1IF Is AC opened (or L Error-Amp without compensator). ‘ 0
  14. 14. «'4- Stabilizing the Converter (ixtn/ l2so9) ‘«i~'§§$ Type 2 compensator Calculator Step3 Select a crossover frequency (about 10kHz or fc <fosc/4 ), for Switching frequency, fosc : 105.00 kHz this example, 10kHz is selected. C, -OSs_oVer frequency’ fc Then complete the table. (<fosc/4) : 10.00 kHz Rupper: 5.346 kOhm Rlower : 1 k0 hm valuesfrom R2 (Rupper/ /Rlower) : 0.842 kOhm (automatically calculated) PWM f5§°S£Zf§, }}’é7§.5§, Vref : 0.520 V values from Vpx (Approximate) : 2.5 V
  15. 15. Stabilizing the Converter (NfllI2309) . _. _._. _._.4 . . _. _._. _.. .4 . 7‘-’°'—'; "‘_'/ ':'""""""', "'_"', "T"""“"""'""’"""“' -__. K. ' '_"r"""1 ' ' '_'_""""1 ' ' *'_"""" . Phase Bat fc / . _. _._. _.. .4 . r _. _._. _.. .1 23¢ Bee I V5 ‘technologies Step4 Read the Gain and Phase value at the crossover treguency (10kHz) from the Bode plot, Then put the values to the table. Parameter extracted from simulation Set: R2=R1, C1=1k, C2=1f Gain (PWM) at foc ( - or + ): Phase (PWM) at foc: -36.242 84.551 Tip: To bring cursor to the fc = 10kHz type “ stxv(10k) " in Search Command. Cursor Search
  16. 16. Stabilizing the Converter (NiIVl2809) -3%<’r§§. .% Step5 Select the phase margin at fc K-factor“ (Choose K and from the table) (> 45 °). Then change the K value K 3 (start from K=2) until it gives the 9 -217 0 (automgtjca/ /y ( satisfied phase margin, for this example K=3 is chosen for Phase Phase margin : 48 (automatically c. ’"‘"9'" = 48 0' (82: 54.655 kOhm‘. (automatically calculated) L V . As the result; R2, 1 C1 : 0.847 nF (automatically calculated) C1 and C2 are (C2: fl pF , (automatically calculated) Ca, 'Cu, ated_ Remark: If K-factor fail to gives the satisfied phase margin, In crease the output capacitor C then try Step1 to Step5 again. 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).
  17. 17. W Bee Stabilizing the Converter (NfllI2309) ‘vii? M»-we 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. U2 L BUCK SW 100uH . 1 rvvv'_i fii rs. .. ( J; :/2‘/ dc % EBSZR ; ‘.’3°"d T _l_ _J_ | The calculated values of ‘ the type 2 elements are: ' ' ‘S : ~/ R2=54.655k, ' / C1=0.874nF , /¢2=97.07pF. Ruppm 5.345s 54.655'K 0.E74n -——-ll- 1kH VP =2.5 f va VREF = u.52 0 *Analysis directives: 70 . AC DEC 100 0.1 lOMEG
  18. 18. Stabilizing the Converter (NfllI2809) Gain and Phase responses after stabilizing‘ I Gain: : T(s) H(s) _ rr—v—v—v1 rr—v—v—v1 rr—v—v—v1 . _____B‘_‘_ _ . . .2.. . . - - — — — — — — — — - ----Phaset9at-fc - . _._ , . . . . _ _ _ __ ——-4 ————l ———4 ‘*1 23¢ Bee I V5 ‘technologies - Phase margin = 48.801 at the cross—over frequency — fc = 9.237kHz. Tip: To bring cursor to the cross—over point (gain = 0dB) type “ stIe(0) " in Search Command. Cursor Search
  19. 19. Load Transient Response Simulation -iii-99.. .‘-‘E2 The converter, that have been stabilized, are connected with step-load to perform load transient response simulation. U2 L 1Cl0.. lH , Load . . . - i ~f0—n—~fi C Rload I1 =0 ‘: T1UCDuF ® I1 ESR 15.5 I2 = o.a 132m TD =10m TF =25u TR =20u 3.3V/16.50 = 0.2A step to 0.2+0.8=1.0A load § Ruppur 5.34BK R2 Cl 5-$.655k 0.574" —ll— § Rlower lk *Analysis directives: VP=2.5 *: ‘ . TRAN O 20ms O lu
  20. 20. Simulation . . it/ feee _. . -; Load3Gurrent---3- Load Transient Response Simulation EOutput Voltage Change; ,». "fit . .'. ' Hg”. :3’. Bee I g‘: Technologies - The simulation results illustrates the transient response of the converter with the stepping load .2A to 1A.
  21. 21. Reference: Load Transient Response Simulation with PWM lC Transient Model '3%<’r§§. .% After the converter have been designed, the PWM IC Transient Model could be applied for more realistic simulation. '- load RON = 10CIm TCICIIJH 1 rvv'v_JZ: © , ‘ S1 D1 C S DIODE T1UUQJF I1 , VIII | C=3.3 Rio. |1=Cl — 12Vdc 2.’t"II 16.5 I I2 = u.a ESR TD =1Dm 132m J TF = Eu I TR =2C| .I PW = cI.43n. '. :0 PER =1 33Mfl&5Q=02A step to 0. 2+0. 8=1.0A load é Rumor 5.3-M34 R2 C1 5-$.655k 0.57-til —il— Rlower 1k *Analysis directives: FoSc= io5K ‘F0 VREF = CI.52 . TRAN O l2ms 0 200m SKIPBP VP=2-5 X Remark: PWM IC Transient Model and Simulations are not included with this package.
  22. 22. : Load Transient Response Simulation _‘y_Bee with PWM IC Transient Model 4% v~= ~»-we Simulation 2.1 Ioutputvoltage Change I I _, _,J I I Z I "‘ 7v"l'. ‘I". .‘. I ' ' I "llilEi. ')rl'i , ‘l' ’| l’l. i'ti‘I. ‘i'il| e"rIit| it'rI. i:i': iI. “l'. ‘[i. ‘iIr| r -t__‘_‘: .‘_‘; "‘l‘V! ::l'(, '.r‘(. :ir‘l": iil. ‘:. ((, ',, (.(3.1". __; .)l‘____: __. _:____; ____; __ jl Load Current | :| i [3 -: -;Z‘: A.: '‘. <ii / The PWM IC Transient Model enables The VOUT‘ RPPLE and others switching characteristics to be included in the simulation. X Remark: PWM IC Transient Model and Simulations are not included with this package.
  23. 23. A. Type 2 Compensation Calculation using Excel ’.5§. .e. .§ Switching frequency, fosc : 105.00 kHz Given spec, datasheet Cross-overfrequency, fc (<fosc/4) 2 10.00 kHz Input the chosen value (about10kHz or <fosc/4 ) Rupper: 5.346 kOhm Given spec, datasheet, or calculated Rlower : 1 kOhm Given spec, datasheet, or value: 1k-10k Ohm R2 (Rupper/ /Rlower) : 0.842 kOhm (automaticallycalculated) PWM Vref: 0.520 V Given spec, datasheet Vp (Approximate) 2 2.5 V Given spec, or calculated, (orleave default 2.5V) Parameter extracted from simulation Set: R2=R2, C1=1k, C2=1f Gain (PWM) at foc ( - or+) : -36.242 dB Readfrom simulation result Phase (PWM) at foc : 84.551 ° Readfrom simulation result K-factor (Chaos K and l9from the tablg) K 3 Input the chosen value (start from k=2) 0 -217 ° (automatically calculated) Phase margin : 48 (automatically calculated) Target value > 45 R2 : 54.655 kOhm (automatically calculated) C 1 : 0.874 n F (automatically calcula ted) C2 : 97.07 p F (automatically calculated)
  24. 24. 23¢ Bee B. Feedback Loop Compensators «as m»»«-« Type2a Compensator Type2b Compensator Type3 Compensator
  25. 25. :3’. Bee C. Simulation Index m rem»-« Simulations Folder name 1. Stabilizing the Converter . ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . . . ac 2. Load Transient Response . ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .. . . stepload Libraries : 1. . .¥bucksw. lib 2. . .¥pwm_ctr. |ib Tool : - Type 2 Compensator Calculator (Excel sheet)

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