SEPIC Converter; Input +30-60V; Output 3.3V 150mA Reference Design PRD1193 FEATURES • • 30V to 60V Input Voltage Range Novel low cost "bootstrap" IC bias method for improved efficiency DESCRIPTION This is an ADP1613-based 30 - 60V input Cascode SEPIC converter which produces 3.3V output at 0 - 150 mA. U1 (ADP1613 boost regulator) serves as the controller IC and Q1 is a Cascode (source-driven) power switch MOSFET. At initial power-up, Q2 (MMBTA06) provides bias power to run the ADP1613. Once the output voltage reaches ~1.5V or so, Q3 attempts to turn off Q2 to save input power. However, while the output voltage is rising, C8 overrides the effect of Q3 by coupling current into the base of Q2 to keep it turned on. This assures that Q2 does not turn off (possibly shutting down the ADP1613) before the output voltage has risen adequately to power the IC. Once the output voltage settles at 3.3V, D2 provides ~3.0V power to the ADP1613, the C8-coupled override decays, and Q3 turns off Q2 for a significant gain in efficiency. Note that the ADP1613 is set for ~650 KHz operation but the 60V to 3.3V conversion requires a duty cycle ~ 6%, which is less than the minimum which the ADP1613 is generally capable. The result is that the converter will tend to "pulse skip" at all values of load current when powered by 60V input. Output ripple should stay within specified limits however. Bench adjustment of compensation values R1-C1 may help improve ripple or dynamic load response, but the values shown are believed to be good. Table 1. Target Specifications (0 to 55 degrees C) Rail Volts Min Volts Nom Volts Max Current Output Ripple +5V 4.9 5 5.1 0 - 150 mA DC 50 mV p-p Vinput 30 45 60 ---- Rev. 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Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved. Reference Design PRD1193 TABLE OF CONTENTS Features ......................................................................................................................................................................1 Description .................................................................................................................................................................1 Revision History .........................................................................................................................................................2 TABLE OF FIGURES Figure 1. Schematic Diagram ................................................................................................................................2 REVISION HISTORY 12/18/2009—Revision 0: Paper Design Schematic Diagram Open Figure 1. Rev. A | Page 2 of 5 Reference Design Table 2. PRD1193 Bill Of Materials Seq. Ref Des. Description 1 C1 3.3 nF 10% X7R 0603 2 C2 Not used 3 C3 C3216JB2A105M 4 C4 100 nF 20% 25V X7R $0.005 5 C5 1 uF 16V X5R 0603 $0.010 6 C6 EEUFC2A220 Panasonic $0.090 Low ESR 22 uF 100V (Series FC) 7 C7 C3216JB2A105M TDK $0.120 Ceramic 1 uF 100V 1206 X7R 8 C8 1 uF 16V X5R 0603 $0.010 9 C10 3.3 nF 10% X7R 0603 $0.010 10 C11 22 uF 20% 6V3 X5R 0805 $0.060 11 C12 EEU-FM0J561 12 C13 22 uF 20% 6V3 X5R 0805 13 D1 MBRS1100 On Semi $0.110 14 D2 BAV19WS Micro Commercial $0.035 15 D3 BAV19WS Micro Commercial $0.035 16 D4 BZX84-C5V1 NXP $0.019 17 L1 MSD7342-473ML Coilcraft $0.620 18 L2 LQH32CN4R7M53L MuRata $0.123 4.7 uH unshielded 19 Q1 FDC3612 Fairchild $0.280 MOSFET 100V SOT-6 20 Q2 MMBTA06 On Semi $0.040 21 Q3 MMBT3904 On Semi $0.015 22 R1 20K 0603 5% $0.002 23 R2 4.99K 1% 0603 $0.003 24 R3 8.45K 1% 0603 $0.003 25 R6 470 ohm 0603 5% $0.002 26 R7 1.0M 1206 1% $0.006 27 R8 200K 0603 5% $0.002 Manufacturer Cost Comment $0.010 TDK Panasonic $0.120 $0.072 Ceramic 1 uF 100V 1206 X7R Low ESR 560 uF 6V3 (Series FM) $0.060 Rev. A | Page 3 of 5 Reference Design PRD1193 Seq. Ref Des. Description 28 R10 1.6K 1206 5% $0.004 29 R11 1.6K 1206 5% $0.004 30 R12 1.6K 1206 5% $0.004 31 R13 20K 0603 5% $0.002 32 R14 220K 1206 5% $0.004 33 R20 47K 0603 5% $0.002 34 R21 47K 0603 5% $0.002 35 U1 ADP1613 $0.700 Total BOM Cost $2.584 Manufacturer Rev. A | Page 4 of 5 Cost Comment Reference Design PRD1193 NOTES ©2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. Error! Unknow Rev. A | Page 5 of 5