CM6900 Application Note A-003A Easy Design a SRC Converter By CM6900G Michael Lee Introduction Recently, resonant DC/DC converter has been accepted by the industry, however, the design of a resonant converter is still foreign to most engineers. make a good design. The important topic is how to Here, we focus on the explanation on how engineers can add simple mathematical formula to design the procedures needed for a resonant converter. This would help engineers to easily and quickly design the product that client request, simplify the design process and time, and solve the puzzle engineers may have for resonant converter. In order to easily explain the design concept of the resonant controller and its relationship with the controller IC, this application note will integrate Champion’s resonant control IC (CM6900 series) as the controller of switching controller design. SRC V.S LLC The resonant controller of AC/DC output mainly uses series resonant as the main structure, it is categorized into two operating zone for load curve. SRC is operated on the resonant point (operated in the inductor load area); LLC is operated below the resonant point and between the second resonant point (operated at the inductor load area). Graph 1 (SRC) and graph 2 (LLC) below gives further explanation. 2008/04/12 Champion Microelectronic Corporation Page 1 CM6900 Application Note A-003A Load Curve at Normal Vin 20 15 Vp in Transformer Vs1 ( Fsw ) Vs2 ( Fsw ) Vs3 ( Fsw ) Vs4 ( Fsw ) 10 Vs5 ( Fsw ) Vs6 ( Fsw ) 5 2 .10 4 4 .10 4 6 .10 4 8 .10 4 1 .10 Fsw Switch Frequency 5 5 1.2 .10 5 1.4 .10 Fr 5 1.6 .10 5 1.8 .10 2 .10 5 Fmax Fmin>=Fr Graph 1: SRC Load Curve From graph 1 SRC load curve, it can be seen that the resonant controller’s operating zone, frequency is from Fmin~Fmax. In other words, the switching frequency Fsw operate above the resonant point Fsw>=Fr. 2008/04/12 Champion Microelectronic Corporation Page 2 CM6900 Application Note A-003A Load Curve at Normal Vin 20 15 Vp in Transformer Vs1( Fsw) Vs2( Fsw) Vs3( Fsw) Vs4( Fsw) 10 Vs5( Fsw) Vs6( Fsw) 5 2 .10 4 4 .10 4 6 .10 4 Fr2 8 .10 4 1 .10 1.2 .10 Fsw Switch Frequency 5 5 1.4 .10 Fr1 5 1.6 .10 5 1.8 .10 5 2 .10 5 Fmax Fmin>=Fr2 Graph 2 LLC Load Curve From graph 1 SRC load curve, it can be seen that the frequency of the resonant controller’s operating zone is from Fmin~Fmax. In other words, when operating above the second resonant point and between Fsw>=Fr2~Fr1, at light load the frequency will be Fsw>Fr1. Therefore, comparing the advantage and disadvantage when designing SRC and LLC, LLC is by far more difficult to design compare to SRC. It is difficult to design if load curve is not simulated, so SRC is much easier to design because it only needs to design on a single resonant point. There will not be design issues even if simulation is not done. So, as to the serial resonant controller, there are two operating zone. SRC is the one with switching frequency operated on the resonant frequency while LLC operates between two resonant points, therefore LLC design is comparatively difficult. 2008/04/12 Champion Microelectronic Corporation Page 3 CM6900 Application Note A-003A Design a SRC Converter 1. Design flow and parameter setting a. Input spec (350Vdc ~ 395Vdc) b. Output spec (normally 5V or 12V/24V) c. Decide resonant frequency (Fr: normally set at 50Khz) d. Decide controller IC (CM6900G) Minimum working frequency (same Fmin and Fr)/Maximum working frequency (Fmax normally set at 200Khz) e. Decide the Q value of resonant frequency (normally set between 0.3 ~ 0.5) f. Structure Choice (below 500W use half bridge CLASS D, above 500W uses standard half bridge or full bridge). 2. Calculation Example (12V/25A 300W) Here we use 300W 12V/25A as an example to explain the design and calculation of SRC resonant converter. Graph 3 is the SRC half bridge circuit; graph 4 is CM6900G circuit and component values used. 2008/04/12 Champion Microelectronic Corporation Page 4 CM6900 Application Note A-003A +VDC D10 SS16 R43 47Ω Q12 9A/500V C30 100pF/1KV DRVH R44 47KΩ C31 PQ-20/16 160uH 47nF/630V 0.8uH/25A 5 7 9A/500V C35 SYNDRVH + C33 + C33 0.1uF/63V 3300uF/16V 3300uF/16V 75A/50V C37 100pF/1KV DRVL 12V L5 Q13 1 Q14 R45 47KΩ 6 T5 D11 SS16 R46 47Ω 75A/50V T4 2 6 5 DRVHGND C32 47nF/630V SYNDRVL Lp(1.5mH) 8 Q15 + C34 C47 3300uF/16V 0.1uF/63V R47 47KΩ ERL-35 R49 47KΩ Graph 3 SRC Half Bridge Circuit +12V R53 2KΩ 1 2 3 VREF R58 430KΩ C50 4 R37 2MΩ 5 R64 100KΩ 1nF/25V R57 1KΩ VREF U6 R55 1.8KΩ 6 7 SD C49 R70 1KΩ 1nF/25V R63 150K R65 100KΩ C58 0.1uF/16V RSET 47KΩ 8 R59 200KΩ C52 47pF/25V Css 0.22uF/25V R71 R72 12KΩ 1KΩ Rset VREF VFB VCC FEAO PRIDRV D_IN- PRIDRVB D_IN+ SRDRV DEAO SRDRVB CSS GND Ilim RT/CT CM6900 C54 0.1uF/25V 12VS 16 15 14 13 12 11 PRIDRVH PRIDRVL SECDRVH RT 47KΩ SECDRVL 10 9 CT C51 C56 620pF/25V NPO0.1uF/25V0.1uF/25V IPLIMIT Graph 4 CM6900G Circuit and component values used 2008/04/12 Champion Microelectronic Corporation Page 5 CM6900 Application Note A-003A Design parameter is as follows: Subject: The Half-bridge power supply design (series resonant converter ) Design specifications. −3 3 k ≡ 10 −6 m ≡ 10 −9 μ ≡ 10 − 12 n ≡ 10 p ≡ 10 Input Specification Vin_max:= 400 Vin_min := 330 Vin_nor := 395 Output Specification Vout1 := 12 Iout1min := 0.01 Iout1max := 12.5 Vripple := 100⋅ m Vout2 := 12 Iout2min := 0.01 Iout2max := 12.5 Vripple := 100⋅ m Pout := ( Vout1⋅ Iout1max) + ( Vout2⋅ Iout2max) Pout = 300 η := 0.96 Watt Power stage Specification Fresonant := 50⋅ k Lm := 6m Bdelta := 2000 Rds := 3⋅ m Gauss Vmosfet := ( Iout1max + Iout2max) ⋅ Rds Q := 0.3 Control Specification use CM6900G Vref := 7.5 Dead_time := 500⋅ n Fmin := 50⋅ k Fmax:= 200⋅ k CM6900 parameter design fosc = 1 / (tRAMP + t DEADTIME) tRAMP = RT * CT * ln((VREF + ICHG*RT -1.25)/(VREF + ICHG*RT -3)) where ICHG = 4*(FEAO-VBE)/RSET tDEADTIME = 2.125V/2.5mA * CT = 850 * CT 1.Dead-time Dead_time := 500⋅ n Dead_time Ct := 850 − 10 Ct = 5.882 × 10 2008/04/12 Ct := 620⋅ p Ct is 620pF Champion Microelectronic Corporation uses NPO material Page 6 CM6900 Application Note A-003A 2.Minimum Frequency Foscmin := Fmin⋅ 2 1 Tramp_max := Rt := Foscmin Tramp_max Ct⋅ ln⎡⎢ −6 − Dead_time Tramp_max = 9.5 × 10 ( Vref − 1.25) ⎤ ⎥ ⎣ ( Vref − 3) ⎦ 4 Rt := 47k Rt = 4.664 × 10 Rt is 47Kohm 3.Maxmum Frequency Foscmax := Fmax⋅ 2 1 Tramp_min := − Dead_time Foscmax −6 Tramp_min = 2 × 10 ⎛ Tramp_min ⎞ ⎤ ⎡ ⎢ 20⋅ Rt − 20⋅ e⎜⎝ Rt ⋅Ct ⎟⎠ ⋅ Rt⎥ ⎣ ⎦ Rset := ⎛⎜ Tramp_min ⎞⎟ Rt ⋅Ct ⎠ − 6.25 4.5⋅ e⎝ 4 Rset := 47⋅ k Rset = 4.669 × 10 Rset is 47Kohm 4.Soft-start capacitor Tsoft := 0.05 ⎛ 7.5⋅ μ ⋅ Tsoft ⎞ ⎟ 2.5 ⎝ ⎠ −7 Css := ⎜ Css = 1.5 × 10 Css is 0.22uF Main transformer design 1.Select a core for power supply PQ-32/30 Ae:1.61 ERL-35 Ae:1.07 Ae := 1.07 Trnum := 1 Topology := 2 Full Bridge=1 Half Bridge =2 2.Dertermine the turn ratio Np/Ns Set normal output voltage is 110% to 120% of transformer secondary output in SRC application 2008/04/12 Champion Microelectronic Corporation Page 7 CM6900 Application Note A-003A Vin_nor Npmin := Topology ⋅ Trnum 8 ⋅ 10 4⋅ Fmin⋅ Bdelta⋅ Ae Npmin = 46.145 Npmin := 43 Primary side coil Vin_nor Topology ⋅Trnum Nratio1 := Ns1 := ( Vout1 + Vmosfet) ⋅ 1.15 Nratio1 = 14.223 Npmin Nratio1 Ns1 = 3.023 Secondary side coil Ns2 = 3.023 Secondary side coil Vin_nor Topology ⋅Trnum Nratio2 := Ns2 := ( Vout2 + Vmosfet) ⋅ 1.15 Nratio2 = 14.223 Npmin Nratio2 Vin_max 8⎞ ⎛ ⎜ Topology ⋅ Trnum ⋅ 10 ⎟ Bmax:= ⎜ ⎟ ⎝ 4⋅ Fmin⋅ Npmin⋅ Ae ⎠ 3 Bmax = 2.173 × 10 Main transformer magnetic flux density 3.Dertermine resonant components Set Q value does not over 1 @ full load at resonant point 2 Ro1 := Vout1⋅ Nratio1 Iout1max Ro1 = 194.194 Output reflex to primary side load Ro2 = 194.194 Output reflex to primary side load 2 Ro2 := Vout2⋅ Nratio2 Iout2max Rot := Ro1⋅ Ro2 ( Ro1 + Ro2) Zo := Q⋅ Rot 2008/04/12 Rot = 97.097 Output reflex to primary side total load Zo = 29.129 Calculate Lr, Cr distinct resistance Champion Microelectronic Corporation Page 8 CM6900 Application Note A-003A Calculation Cr Lr=Zo*Cr 2 ⎡ ⎛ 1 ⎞ ⎤⎥ ⎢ ⎜ ⎟ ⎢ ⎝ 2⋅ πFresonant ⎠ ⎥ Cr := ⎢ ⎥ 2 Zo ⎣ ⎦ −7 Cr := 86⋅ n −5 Lr := 120⋅ μ Cr = 1.093 × 10 Resonant Capacitor Calculation Lr 2 Lr := Zo ⋅ Cr Fresonant := Lr = 7.297 × 10 1 4 Fresonant = 4.954 × 10 2⋅ π⋅ Lr⋅ Cr Resonant Inductor Resonant Frequency Lr Q := Cr Q = 0.385 Rot Q value Calculation Lr voltage stress VLr:= Q⋅ Vin_max VLr = 76.942 Topology Resonant inductor voltage PQ-20/16 Ae:0.64 Blr_max:= 2500 Aelr := 0.64 Nlr := VLr Aelr⋅ Blr_max⋅ 4.44⋅ Fmin 8 ⋅ 10 Nlr = 21.662 Resonant inductor coil Calculation Cr voltage stress VCr_ac := VLr Vin_max VCr := + VCr_ac 2 VCr = 276.942 Resonant Inductor Voltage Resonant inductor voltage value is double or more Suggest to use 800V high current durance MPP inductor 2008/04/12 Champion Microelectronic Corporation Page 9 CM6900 Application Note A-003A Load Curve at Maxmun Vin 20 15 Vp in Transformer Vs1 ( Fsw ) Vs2 ( Fsw ) Vs3 ( Fsw ) Vs4 ( Fsw ) 10 Vs5 ( Fsw ) Vs6 ( Fsw ) 5 2 .10 4 4 .10 6 .10 4 Graph 5 2008/04/12 4 8 .10 4 5 5 1 .10 1.2 .10 Fsw Switch Frequency 5 1.4 .10 5 1.6 .10 5 1.8 .10 2 .10 SRC high voltage input load curve Champion Microelectronic Corporation Page 10 5 CM6900 Application Note A-003A Load Curve at Normal Vin 20 15 Vp in Transformer Vs1 ( Fsw ) Vs2 ( Fsw ) Vs3 ( Fsw ) Vs4 ( Fsw ) 10 Vs5 ( Fsw ) Vs6 ( Fsw ) 5 2 .10 4 4 .10 Graph 6 2008/04/12 4 6 .10 4 8 .10 4 1 .10 Fsw Switch Frequency 5 5 1.2 .10 5 1.4 .10 5 1.6 .10 5 1.8 .10 2 .10 SRC regular input voltage load curve Champion Microelectronic Corporation Page 11 5 CM6900 Application Note A-003A Load Curve at Minmun Vin 20 15 Vp in Transformer Vs1( Fsw) Vs2( Fsw) Vs3( Fsw) Vs4( Fsw) 10 Vs5( Fsw) Vs6( Fsw) 5 2 .10 4 4 .10 4 6 .10 4 8 .10 4 1 .10 1.2 .10 Fsw Switch Frequency 5 5 1.4 .10 5 1.6 .10 5 1.8 .10 5 2 .10 5 Graph 7 SRC low input voltage load curve Calculation Ripple current of Cout Iripple := 0.448⋅ ( Iout1max + Iout2max) Iripple = 11.2 Output inductor ripple current Suggest inductor ripple current endurance need to be 30% more than needed 2008/04/12 Champion Microelectronic Corporation Page 12 CM6900 Application Note A-003A 4.Feedback loop compensation design CM6900 GM Modeling −6 6 Ro := 1⋅ 10 −6 Gm := 135⋅ 10 Iodrv_max := 13⋅ 10 CM6900 GM compensation network A. Voltage Loop FM Compensation R1 := 150⋅ k 1 Z1 := 2⋅ π⋅ R1⋅ C1 1 P1 := 2⋅ π⋅ Ro⋅ C1 1 P2 := 2⋅ π⋅ R1⋅ C2 2008/04/12 C1 := 1⋅ n C2 := 0.47⋅ n 3 Z1 = 1.061 × 10 P1 = 159.155 3 P2 = 2.258 × 10 Champion Microelectronic Corporation Page 13 CM6900 Application Note A-003A A ( Fsw) := Gm⋅ Ro⋅ (1 + R1⋅ C1⋅ 2⋅ π⋅ Fsw) (1 + R1⋅ C2⋅ 2⋅ π⋅ Fsw)⋅ ( 1 + Ro⋅ C1⋅ 2⋅ π⋅ Fsw) Bode Plot 1 .10 3 Loop Gain of Compensator 100 10 A( Fsw) 1 0.1 0.01 1 10 1 .10 3 100 1 .10 1 .10 4 5 Fsw Frequency B. Voltage Loop Duty Compensation High Loop Gain for Duty Compensation Middle Loop Gain for Duty Compensation 2008/04/12 Champion Microelectronic Corporation Page 14 CM6900 Application Note A-003A 6 R1 := 100⋅ k Ro := 1⋅ 10 −6 P1 := P2 := C2 := 0.001⋅ p R2 := 240⋅ k Gm := 135⋅ 10 Z1 := C1 := 1⋅ n 1 3 Z1 = 1.592 × 10 2⋅ π⋅ R1⋅ C1 1 P1 = 159.155 2⋅ π⋅ Ro⋅ C1 1 9 P2 = 1.592 × 10 2⋅ π⋅ R1⋅ C2 A ( Fsw) := Gm⋅ Ro⋅ R2 Ro + R2 ⋅ ( 1 + R1⋅ C1⋅ 2⋅ π⋅ Fsw) ( 1 + R1⋅ C2⋅ 2⋅ π⋅ Fsw) ⋅ (1 + Ro⋅ C1⋅ 2⋅ π⋅ Fsw) Bode Plot Loop Gain of Compensator 100 10 A( Fsw) 1 0.1 1 10 1 .10 3 100 1 .10 1 .10 4 5 Fsw Frequency 2008/04/12 Champion Microelectronic Corporation Page 15 CM6900 Application Note A-003A Typical application Circuit +VDC D10 SS16 Q12 R43 47Ω CMT08N50 C30 100pF/1KV DRVH R44 47KΩ C31 PQ-20/16 2 6 5 DRVHGND T5 47nF/630V C32 47nF/630V 10 CMT08N50 C37 100pF/1KV DRVL CMT60N06 R45 47KΩ L5 13 0.8uH/10A 14 15 24VSYNDRVH ERL-35 C35 0.1uF/63V CMT60N06 16 Q15 + C33 + C34 C36 1000uF/35V 1000uF/35V 0.1uF/63V 0.1uF/63V R47 47KΩ 9 R49 47KΩ L6 12VI+ 10 11 Q16 12 +12V 24VSYNDRVL SI4386ADY 2uH/3A C40 R48 +24V Q13 1 Q14 T4 11 D11 SS16 R46 47Ω 24VSYNDRVL Lp(1.5mH) 0.1uF/63V Q17 + C38 + C39 1000uF/16V 1000uF/16V C41 0.1uF/63V D12 IPLIMIT SI4386ADY 1KΩ C42 470nF/25V R50 1KΩ BAV99 24VSYNDRVH D13 BAV99 2008/04/12 Champion Microelectronic Corporation Page 16 C47 CM6900 Application Note A-003A 12VS Q18 BC817 C44 + C43 T6 100uF/25V 5 Q20 2.2uF/63V DRVH BC807 6 3 DRVHGND 12VS +12V +24V +12V 12VS 2 R53 6.8KΩ 7 Q24 BC817 D14 R54 15K DRVL 8 SCD12 R55 390Ω U6 1 2 3 VREF R58 430KΩ 4 R58 5 C50 R64 100KΩ 2MΩ 6 1nF/25V 7 SD R57 910Ω EE19 Q25 R56 620Ω C49 R70 1KΩ C51 8 R59 Rset VREF VFB VCC FEAO PRIDRV D_IN- PRIDRVB D_IN+ SRDRV DEAO SRDRVB CSS GND Ilim RT/CT 1nF/25V R63 0.1uF/16V 150K R65 100KΩ R66 47KΩ 390KΩ C52 47pF/25V C53 0.1uF/25V R58 100KΩ D5 R71 C29 12KΩ 0.1uF/25V BAV99 CM6900 R72 1KΩ BC807 12VS C54 16 VREF 15 12VS 14 Q19 BC817 13 12 R51 11 4.7Ω 1/4W 24VSYNDRVH 10 12VS R73 47KΩ 9 Q22 VREF BC807 C55 620pF/25VN 0.1uF/25V C56 0.1uF/25V 12VS Q21 BC817 R52 IPLIMIT 4.7Ω 1/4W 24VSYNDRVL Q23 BC807 3. Conclusion It is very easy to design serial resonant converter, above designs can all be achieved by using the mathcad file Champion provide. This file provides a fast and easy design procedure and simulation result; user can purchase mathcad software and download the file Champion provides to design the calculation formula most appropriate for its serial resonant converter. Champion will update the matchcad file as needed to assist the users of CM6900 series for enhanced design parameter functions. HsinChu Headquarter Sales & Marketing 5F, No. 11, Park Avenue II, Science-Based Industrial Park, HsinChu City, Taiwan T E L : +886-3-5679979 F A X : +886-3-5679909 7F-6, No.32, Sec. 1, Chenggong Rd., Nangang District, Taipei City 115, Taiwan, R.O.C. 2008/04/12 T E L : +886-2-2788 0558 F A X : +886-2-2788 2985 Champion Microelectronic Corporation Page 17