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Low Cost PolyPhase DC / DC Converter Delivers High Current

Design Note 234 Wei Chen

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Low Cost PolyPhase DC / DC Converter Delivers High Current
Design Note 234 Wei Chen
Introduction The LTC®1929 / LTC1929-PG are current mode DC / DC controllers that drive two synchronous buck stages out of phase. The 2-phase architecture reduces the number of input and output capacitors without increasing the switching frequency. The relatively low switching frequency and integrated high current MOSFET drivers help obtain high power conversion efficiency for low voltage, high current applications. Because of output ripple current cancellation, lower value inductors can be used, resulting in faster load transient response. Power good indication can be added by using the LTC1929-PG. Typical applications include high current (up to 40A) low voltage ( 6V) power supplies for microprocessors, memory arrays and ASICs.
1000pF
, LTC and LT are registered trademarks of Linear Technology Corporation. PolyPhase is a trademark of Linear Technology Corporation.
1µF 1µF
12VIN+
10 Q1 NC TG1 SW1 BOOST1 VIN BG1 EXTVCC INTVCC PGND BG2 BOOST2 SW2 TG2 28 27 26 25 24 23 22 21 20 19 18 17 16 15 Q5 Q6 MBRS320T3 0.47µF Q4 L2 1.6µH R8 0.003 1µF 0.47µF Q3 Q2 MBRS320T3 L1 1.6µH R4 0.003
SENSE1 -
BAT54A
VOS + SENSE2 -
SENSE2 + AMPMD
1000pF
C19 51
C20 51 1µF
VOUT + 3.3V / 30A VOUT -
VOSENSE - B0 B1 OPTIONAL CIRCUIT FOR 4-BIT VID OUTPUT PROGRAMMING B2 B3
DN234 F01
VOSENSE +
Figure 1. Schematic Diagram of a 30A Power Supply
12VIN LTC1629 VIN OPEN 90° TG2 180° 2-CHANNEL BUCK 2.5VOUT / 30A
DN234 F02
Figure 2. Efficiency vs Load Current
INTVCC RA VDIFFOUT QA 2N3904 EAIN 2N3904 6.81k 36.5k
PHASMD BG2 TG1 CLKOUT BG1 LTC1929 PLLIN VIN TG2 BG2 TG1 BG1 90° 270° 0°
2-CHANNEL BUCK
1.8VOUT / 30A
DN234 F04
Figure 4. Block Diagram of a 2-Output Power Supply
Figure 3. Optional Circuit to Modify Foldback Current Limit
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dn234f LT / TP 0700 340K · PRINTED IN THE USA
http://www.linear-tech.com / go / dnLTC1929
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com