LTC1873| Datasheet

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LTC1873 Dual 550kHz Synchronous 2-Phase Switching Regulator Controller with 5-Bit VID
FEATURES
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DESCRIPTIO

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Two Independent PWM Controllers in One Package Side 1 Output Is Compliant with Intel Desktop VRM 8.4 Specifications (Includes 5-Bit VID DAC) 1.3V to 3.5V Output Voltage with 50mV/100mV Steps Two Sides Run Out-of-Phase to Minimize CIN All N-Channel External MOSFET Architecture No External Current Sense Resistors Required Precison Internal 0.8V 1% Reference 550kHz Switching Frequency Minimizes External Component Size Very Fast Transient Response Up to 25A Output Current per Channel Low Shutdown Current: < 100uA Small 28-Pin SSOP Package

APPLICATIO S
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Microprocessor Core and I/O Supplies Multiple Logic Supply Generator High Efficiency Power Conversion Chipset Power Supply

The LTC 1873 is a dual switching regulator controller optimized for high efficiency with low input voltages. It includes two complete, on-chip, independent switching regulator controllers. Each is designed to drive a pair of external N-channel MOSFETs in a voltage mode feedback, synchronous buck configuration. The LTC1873 includes digital output voltage adjustment on side 1 that conforms to the Intel Desktop VID specification. A constant-frequency, true PWM design minimizes external component size and cost and optimizes load transient performance. The synchronous buck architecture automatically shifts to discontinuous and then to Burst ModeTM operation as the output load decreases, ensuring maximum efficiency over a wide range of load currents. The LTC1873 features an onboard reference trimmed to 1% and delivers better than 1.5% regulation at the converter outputs over all combinations of line, load and temperature. Each channel can be enabled independently; with both channels disabled, the LTC1873 shuts dow
n and supply current drops below 100uA.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIO
4.5V TO 5.5V

Low Cost Desktop CPU Supply with RDRAM Keepalive
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10 4.75k 0.1% 330pF CIN MBR0530T 10uF VCC FB2 56pF COMP2 1k QSS1 STBY/ON 1k QSS2 0.1uF SENSE 220pF FB1 39pF COMP1 FCB 5-BIT VID VID4:0 SGND RUN/SS2 RUN/SS1 PVCC BOOST2 TG2 SW2 BG2 IMAX2 MBR0530T QT1B TG1 SW1 BG1 33k IMAX1 PGND QB1B QB1A QT1A 1uF L1 VCORE 1.3V TO 3.5V 20A COUT1 CIN = SANYO 10MV1200GX (6 IN PARALLEL) COUT1 = SANYO 6MV1500GX (8 IN PARALLEL) COUT2 = SANYO 6MV1500GX (3 IN PARALLEL) L1: 1uH SUMIDA CEP125-1R0MC-H L2: 2.2uH COILTRONICS UP2B-2R2 QSS1, QSS2: MOTOROLA MMBT3904LT1 QT1A, QT1B, QB1A, QB1B: FAIRCHILD FDS6670A QT2, QB2: 1/2 SILICONIX Si4966 BOOST1 47k QB2 QT2 1uF L2 16.9k 0.1% VRDRAM 2.5V/7A 2.45V/100mA STANDBY COUT2 IN 1uF OUT 16.2k 0.1%

LT1761 GND ADJ

10k 0.1% 68k

LTC1873 FAULT

56k

U
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1873 TA01