CM6900 Application Note A-003A Easy Design a SRC Converter By CM6900G Michael Lee Introduction 近年來，共振式 DC/DC 轉換器已經為業界所接受，但是由於共振式轉換器的 設計，對大多數的電源工程師而言，仍屬陌生，如何做好設計成為重要的課題。在 此主要是針對電源工程師對於共振式轉換器設計的流程與方法，在加入簡易的數學 計算做說明，也希望幫助工程師能簡單快速的設計出客戶所需要的電源產品，簡化 設計的流程與時間，同時也解決了工程師對共振式轉換器的困惑，當然本文會結合 本公司的共振式控制 IC 做為轉換器設計的控制器，以方便說明共振轉換器的設計 概念與控制 IC 之間的關係。 SRC V.S LLC 用於直流輸出之共振式轉換器主要以串聯共振(Series resonant)為主架構，主 要分成兩種負載曲線的操作區域，SRC 操作在共振點之上(操作在電感性負載區)， LLC 操作在共振點之下與第二共振點之間(操作在電容性負載區間)，以圖一 SRC； 圖二 LLC 為負載曲線圖來做說明。 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 圖一 SRC 負載曲線圖 從圖一的 SRC 負載曲線圖可以說明一個重點，共振式轉換器的操作區域頻率由 Fmin~Fmax，也就是說切換頻率 Fsw 操作在共振點以上 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 圖二 LLC 負載曲線圖 從圖一的 LLC 負載曲線圖可以說明一個重點，共振式轉換器的操作區域頻率由 Fmin~Fmax 也就是說操作在第二共振點以上 Fsw>=Fr2~Fr1 之間，在輕載時頻率會 Fsw>Fr1 所以比較 SRC 與 LLC 在設計上的優缺點，LLC 遠比 SRC 複雜難設計，如 果不做負載曲線模擬的話是很難設計，所以 SRC 的單共振點在設計上就簡單許多， 如果不做模擬負載曲線模擬也不容易有設計上的問題。 所以就串聯共振式轉換器而言，就是分兩種操作區域，SRC 就是切換頻率操作 在共振頻率之上，LLC 就是切換頻率操作在兩個共振點之間，所以 LLC 設計相對比 較難。 2008/04/12 Champion Microelectronic Corporation Page 3 CM6900 Application Note A-003A Design a SRC Converter 一、 設計流程與參數設定 a. 輸入規格(350Vdc~395Vdc) b. 輸出規格(一般 5V 或 12V/24V) c. 決定共振頻率(Fr:一般取 50Khz) d. 決定控制 IC(CM6900G)最低工作頻率(Fmin 與 Fr 相同)/最高工作頻 率(Fmax 一般取 200Khz) e. 決定共振頻率下的 Q 值:(一般取 0.3~0.5) f. 架構選擇(500W 以下用半橋 CLASS D，500W 以上可用標準半橋或全 橋) 二、 計算範例(12V/25A 300W) 在此以 300W 12V/25A 作為範例，說明 SRC 共振式轉換器之設計與計 算，圖三為 SRC 半橋電路，圖四為 CM6900G 之電路與使用元件值 +VDC D10 SS16 R43 47Ω Q12 9A/500V C30 100pF/1KV DRVH R44 47KΩ C31 PQ-20/16 160uH 47nF/630V 2 6 5 DRVHGND C32 47nF/630V SYNDRVL Lp(1.5mH) 75A/50V T4 R45 47KΩ T5 12V L5 6 Q13 0.8uH/25A D11 SS16 5 1 Q14 R46 47Ω 7 9A/500V R49 47KΩ 8 C35 + C33 + C33 0.1uF/63V 3300uF/16V 3300uF/16V 75A/50V C37 100pF/1KV DRVL SYNDRVH Q15 + C34 C47 3300uF/16V 0.1uF/63V R47 47KΩ ERL-35 圖三 SRC 半橋電路 2008/04/12 Champion Microelectronic Corporation Page 4 CM6900 Application Note A-003A +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 C58 R65 100KΩ 0.1uF/16V RSET 47KΩ 8 R59 200KΩ C52 47pF/25V Css 0.22uF/25V R71 R72 12KΩ 1KΩ Rset VREF VFB VCC FEAO D_IN- PRIDRV PRIDRVB D_IN+ SRDRV DEAO SRDRVB CSS GND Ilim RT/CT 12VS 16 15 14 PRIDRVH 13 PRIDRVL 12 SECDRVH 11 RT 47KΩ SECDRVL 10 9 CM6900 CT C54 C51 C56 620pF/25V NPO0.1uF/25V0.1uF/25V 0.1uF/25V IPLIMIT 圖四 CM6900G 電路與使用元件值 設計參數如下: Subject : The Half-bridge power supply design (serise resonant converter ) Design specifications. 3 k ≡ 10 −3 −6 m ≡ 10 μ ≡ 10 −9 − 12 n ≡ 10 p ≡ 10 Input Specifecation Vin_max:= 400 Vin_min := 330 Vin_nor := 395 Output Specifecation 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 Watte Power stage Specifecation Fresonant := 50⋅ k Lm := 6m Bdelta := 2000 Rds := 3⋅ m Gauss Vmosfet := ( Iout1max + Iout2max) ⋅ Rds Q := 0.3 2008/04/12 Champion Microelectronic Corporation Page 5 CM6900 Application Note A-003A 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 := 620⋅ p Ct = 5.882 × 10 Ct 取 620pF 使用 NPO 材質 2.Minimum Frequency Foscmin := Fmin⋅ 2 1 Tramp_max := Rt := Foscmin Tramp_max Ct⋅ ln⎡⎢ − Dead_time −6 Tramp_max = 9.5 × 10 ( Vref − 1.25) ⎤ ⎥ ⎣ ( Vref − 3) ⎦ 4 Rt := 47k Rt = 4.664 × 10 Rt 取 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 = 4.669 × 10 2008/04/12 Rset := 47⋅ k Rset 取 47Kohm Champion Microelectronic Corporation Page 6 CM6900 Application Note A-003A 4.Soft-start capacitor Tsoft := 0.05 ⎛ 7.5⋅ μ ⋅ Tsoft ⎞ ⎟ 2.5 ⎝ ⎠ −7 Css := ⎜ Css = 1.5 × 10 Css 取 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 turns ratio Np/Ns Set normal output voltage is 110% to 120% application Vin_nor Npmin := Topology ⋅ Trnum of transformer secondary output in SRC 8 ⋅ 10 4⋅ Fmin⋅ Bdelta⋅ Ae Npmin = 46.145 Npmin := 43 一次側繞組 Vin_nor Nratio1 := Ns1 := Topology ⋅Trnum ( Vout1 + Vmosfet) ⋅ 1.15 Nratio1 = 14.223 Npmin Nratio1 Ns1 = 3.023 二次側繞組 Ns2 = 3.023 二次側繞組 Vin_nor Nratio2 := Ns2 := Topology ⋅Trnum ( Vout2 + Vmosfet) ⋅ 1.15 Npmin Nratio2 Vin_max 8⎞ ⎛ ⎜ Topology ⋅ Trnum ⋅ 10 ⎟ Bmax:= ⎜ ⎟ ⎝ 4⋅ Fmin⋅ Npmin⋅ Ae ⎠ 2008/04/12 Nratio2 = 14.223 3 Bmax = 2.173 × 10 Champion Microelectronic Corporation 主變壓器磁通密度 Page 7 CM6900 Application Note A-003A 3.Dertermine resonant components Set Q value does not over 1 @ full load at resonant point 2 Ro1 := Vout1⋅ Nratio1 Iout1max Ro1 = 194.194 輸出反射至一次側之負載 Ro2 = 194.194 輸出反射至一次側之負載 Rot = 97.097 輸出反射至一次側之總負載 Zo = 29.129 計算 Lr,Cr 之特性阻抗 2 Ro2 := Vout2⋅ Nratio2 Iout2max Rot := Ro1⋅ Ro2 ( Ro1 + Ro2) Zo := Q⋅ Rot Calculation Cr Lr=Zo*Cr 2 ⎡ ⎛ 1 ⎞ ⎤⎥ ⎢ ⎜ ⎟ ⎢ ⎝ 2⋅ πFresonant ⎠ ⎥ Cr := ⎢ ⎥ 2 Zo ⎣ ⎦ −7 Cr := 86⋅ n 共振電容 −5 Lr := 120⋅ μ 共振電感 Cr = 1.093 × 10 Calculation Lr 2 Lr := Zo ⋅ Cr Fresonant := Lr = 7.297 × 10 1 2⋅ π⋅ Lr⋅ Cr 4 Fresonant = 4.954 × 10 共振頻率 Lr Q := Cr Q = 0.385 Rot Q值 Calculation Lr voltage stress VLr:= Q⋅ Vin_max VLr = 76.942 Topology 2008/04/12 Champion Microelectronic Corporation 共振電感電壓 Page 8 CM6900 Application Note A-003A PQ-20/16 Ae:0.64 Blr_max:= 2500 Aelr := 0.64 Nlr := VLr 8 Aelr⋅ Blr_max⋅ 4.44⋅ Fmin ⋅ 10 Nlr = 21.662 共振電感圈數 Calculation Cr voltage stress VCr_ac := VLr Vin_max VCr := + VCr_ac 2 VCr = 276.942 共振電容電壓 共振電容耐壓取兩倍以上 建議用 800V 高耐流 MPP 電容 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 4 6 .10 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 圖五 SRC 高壓輸入負載曲線圖 2008/04/12 Champion Microelectronic Corporation Page 9 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 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 圖六 SRC 正常輸入電壓時之負載曲線圖 2008/04/12 Champion Microelectronic Corporation Page 10 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 圖七 SRC 低輸入電壓時之負載曲線圖 Calculation Ripple current of Cout Iripple := 0.448⋅ ( Iout1max + Iout2max) Iripple = 11.2 輸出電容之漣波電流 建議電容耐漣波電流需大於所需之 30% 2008/04/12 Champion Microelectronic Corporation Page 11 CM6900 Application Note A-003A 4.Feedback loop compensation design CM6900 GM Modeling 6 Ro := 1⋅ 10 −6 −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 12 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 13 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 14 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 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 CMT60N06 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 15 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 BAV99 C29 12KΩ 0.1uF/25V 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 三、總結: 設計串聯共振式轉換器十分簡單，上述的設計皆可以虹冠所提供之 mathcad 檔案來設計，此檔案提供一快速簡單的設計流程與模擬結果，使用者可 以自行加入任何其他需要計算之方程式，使其更為完備。使用者可自行購買 mathcad 軟體載入虹冠所提供之檔案方便設計出更適合串聯共振式轉換器之計算 式，加速設計與簡化設計流程，針對串聯共振式轉換器的設計虹冠電子會不定期更 新 mathcad 檔案，提供使用 CM6900 系列 IC 應用於共振式轉換器之設計者，協助 加速設計與更多設計參數功能。 2008/04/12 Champion Microelectronic Corporation Page 16 CM6900 Application Note A-003A IMPORTANT NOTICE Champion Microelectronic Corporation (CMC) reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. A few applications using integrated circuit products may involve potential risks of death, personal injury, or severe property or environmental damage. CMC integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. Use of CMC products in such applications is understood to be fully at the risk of the customer. In order to minimize risks associated with the customer’s applications, the customer should provide adequate design and operating safeguards. HsinChu Headquarter Sales & Marketing 5F, No. 11, Park Avenue II, Science-Based Industrial Park, HsinChu City, Taiwan 7F-6, No.32, Sec. 1, Chenggong Rd., Nangang District, Taipei City 115, Taiwan R.O.C T E L : +886-3-567 9979 F A X : +886-3-567 9909 http://www.champion-micro.com T E L : +886-2-2788 0558 F A X : +886-2-2788 2985 2008/04/12 Champion Microelectronic Corporation Page 17