Design Note Chen Introduction LTC1929/LTC1929-PG current mode DC/

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Design Note Chen Introduction LTC1929/LTC1929-PG current mode DC/

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Cost PolyPhaseDC/DC Converter Delivers High Current
Design Note Chen
Introduction LTC1929/LTC1929-PG current mode DC/DC controllers that drive synchronous buck stages phase. 2-phase architecture reduces number input output capacitors without increasing switching frequency. relatively switching frequency integrated high current MOSFET drivers help obtain high power conversion efficiency voltage, high current applications. Because output ripple current cancellation, lower value inductors used, resulting faster load transient response. Power good indication added using LTC1929-PG. Typical applications include high current 40A) voltage power supplies microprocessors, memory arrays ASICs.
1000pF
Design Example Figure shows schematic diagram power supply with input 3.3V output. With only tiny SO-8 MOSFETs profile surface mount inductors, greater than efficiency maintained throughout load range between 30A, shown Figure
registered trademarks Linear Technology Corporation. PolyPhase trademark Linear Technology Corporation.
270µF
12VIN+
0.1µF 0.1µF 680pF 470pF 470pF 8.06k 74HC125 0.1µF 25.5k LTC1929 RUN/SS SENSE1 EAIN PLLFLTR PLLIN SGND VDIFFOUT
BOOST1 EXTVCC INTVCC PGND BOOST2 MBRS320T3 0.47µF 1.6µH 0.003 0.47µF MBRS320T3 1.6µH 0.003
SENSE1
10µF
BAT54A
SENSE2
SENSE2 AMPMD
1000pF
KEMET T510X477M006AS C28: 16SP27OM OS-CON CAPS FDS6670A FDS7760A SUMIDA CEPH149-IR6MC
VOUT 3.3V/30A VOUT
VOSENSE OPTIONAL CIRCUIT 4-BIT OUTPUT PROGRAMMING
DN234
VOSENSE
Figure Schematic Diagram Power Supply
07/00/234
VOUT 3.3V 300kHz LOAD CURRENT
When output voltage drops below nominal value, will turn maintain constant voltage EAIN even though output voltage decreases. Consequently, constant current limit achieved long saturated. foldback current limit triggered, parallel combination will produce EAIN voltage about 0.65V. adjusted program threshold foldback current limiting. connects INTVCC instead VDIFFOUT, constant current limit will maintained under shortcircuit condition. Multiphase Applications LTC1929 provides 2-phase operation output current 40A. applications with very high output current 40A) multiple outputs, multiphase operation usually preferred. LTC1629 should then used because PHASMD CLKOUT pins enable multiphase operation. application information high current, single output design found LTC1629 data sheet Design Note 215. Figure shows example 2-output power supply using LTC1629 LTC1929. While each output sees 2-phase ripple current, common input sees 4-phase operation. input ripple current greatly reduced.
12VIN LTC1629 OPEN 180° 2-CHANNEL BUCK 2.5VOUT /30A
EFFICIENCY
DN234
Figure Efficiency Load Current
Active voltage positioning employed this design reduce number output capacitors (refer Design Solutions more details active voltage positioning). optional resistors provide active voltage positioning with loss efficiency. Because 2-phase operation, only OS-CON input capacitors three tantalum output capacitors needed. single-phase configuration were used, four OS-CON input capacitors nine tantalum output capacitors would needed. Overcurrent Limit LTC1929 built-in foldback current limit. When output current exceeds limit, output voltage decreases. output voltage drops below nominal output, output current limit folds back. This feature protects power supply from overheating result abnormal operating conditions such output short circuits. application requires different output voltage threshold activate foldback current limiting defeat foldback current limit entirely, circuit shown Figure used.
INTVCC VDIFFOUT 2N3904 EAIN 2N3904 6.81k 36.5k
PHASMD CLKOUT LTC1929 PLLIN 270°
2-CHANNEL BUCK
1.8VOUT /30A
DN234
Figure Block Diagram 2-Output Power Supply
Figure Optional Circuit Modify Foldback Current Limit
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Conclusion LTC1929-PG provides cost, high efficiency power solution voltage, high current applications. using multiple LTC1929s LTC1629s, multiphase operation configured either single output high current 40A) applications multioutput applications. Refer data sheets, Design Note Application Note more information. literature Switching Regulators, call 1-800-4-LINEAR. applications help, call (408) 432-1900, Ext. 2593
dn234f LT/TP 0700 340K PRINTED
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408)432-1900 FAX: (408) 434-0507 www.linear-tech.com
LINEAR TECHNOLOGY CORPORATION 2000

Design Note Chen Introduction LTC1929/LTC1929-PG current mode DC/

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