SY50282FAC

Application Note: AN_SY50282 Buck Regulator with CC/CV control Preliminary Specification General Description Features The SY50282 is a PWM controller with several features to enhance performance of Buck converters. It integrates a MOSFET with 500V breakdown voltage to decrease physical volume. Both current and voltage regulation are achieved by the controller. It drives the Buck converter in the quasi-resonant mode to achieve higher efficiency and better EMI performance. Ordering Information • Fast Startup ( VBUS 264V × 1.414 = =186kΩ I VIN_OVP 2mA Sil R ST < Set RST AN_SY50282 Rev.0.2 Silergy Corp. Confidential- Prepared for Customer Use Only 11 AN_SY50282 R ST =4.7M (b) Design CVIN VBUS -IST ) × t ST ( 90V × 1.414 -15µA) × 1.5s R ST 4.7MΩ CVIN = = =1.3µF VVIN_ON 14V ( Set CVIN CVIN =1µF #8 Set current sense resistor to achieve ideal output current 0.25A tia l-P re p IOUT,LIM ar ed Known conditions at this step VREF 0.675V The current sense resistor is VREF RISET = = 1.04 2 I OUT ⋅ 1.3 VCOMP _ MAX 0.9 RISET _MIN = = = 0.88 I PK 1.02 fo r Refer to constant-current control fid en Because the saturation current of Mosfet is 1.4A, the current limit is set in 1.02A to consider the margin, so the sense resistance is not less than 0.88Ohm.(The circuit has a good start-up performance in 250mA output when sense resistor is set in 0.88Ohm. ) .C on #7. Set ZCS pin Refer to VOUT Co rp First identify RZCSU need for line regulation. Parameters Designed RZCSU 200kΩ er gy Then compute RZCSD Sil Conditions VOUT 12V RZCSU 200kΩ R ZCSU 200K R ZCSD = = = 22.1K VOUT 12V − 1) -1 ( 1.25V VZCS,REF VZCS_REF 1.25V R ZCSD =22kΩ #10 final result AN_SY50282 Rev.0.2 Silergy Corp. Confidential- Prepared for Customer Use Only 12 Sil er gy Co rp .C on fid en tia l-P re p ar ed fo r AN_SY50282 AN_SY50282 Rev.0.2 Silergy Corp. Confidential- Prepared for Customer Use Only 13 AN_SY50282 4.80 - 5.00 .C on 1.40 - 1.60 0.25 base 0.18 - 0.25 en ° -8 fid 0 45° 0.25 - 0.50 tia l-P re p 0.60 Recommended Pad Layout 1.27 (TYP) Co rp 0.60 - 0.85 0.30 – 0.50 0.08 - 0.25 ar ed fo r 5.40 3.80 - 4.00 1.27 TYP 5.80 - 6.20 6.10 1.55 SO8 Package Outline & PCB Layout Design Sil er gy Notes: All dimensions are in millimeters. All dimensions don’t include mold flash & metal burr. AN_SY50282 Rev.0.2 Silergy Corp. Confidential- Prepared for Customer Use Only 14