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LTC3719

2-Phase, High Efficiency, Step-Down Controller for AMD Opteron™ CPUs

Linear Technology 

LTC3719

2-Phase, High Efficiency,

Step-Down Controller for

AMD Opteron™ CPUs

FEATURES

s Output Stages Operate Antiphase Reducing Input

and Output Capacitance Requirements and Power

Supply Induced Noise

s Dual Input Supply Capability for Load Sharing

s 5-Bit AMD CPU VID Code:

VOUT = 0.8V to 1.55V

s ±1% Output Voltage Accuracy

s True Remote Sensing Differential Amplifier

s Power Good Output Voltage Monitor

s Supports Active Voltage Positioning

s Current Mode Control Ensures Current Sharing

s OPTI-LOOP® Compensation Minimizes COUT

s Three Operational Modes: PWM, Burst and Cycle Skip

s Programmable Fixed Frequency: 150kHz to 300kHz

s Wide VIN Range: 4V to 36V Operation

s Adjustable Soft-Start Current Ramping

s Internal Current Foldback and Short-Circuit Shutdown

s Overvoltage Soft Latch Eliminates Nuisance Trips

s Available in 36-LUead Narrow (0.209) SSOP Package

APPLICATIO S

s Servers and Workstations

, LTC and LT are registered trademarks of Linear Technology Corporation.

OPTI-LOOP and Burst Mode are registered trademarks of Linear Technology Corporation.

AMD Opteron is a trademark of Advanced Micro Devices, Inc.

DESCRIPTIO

The LTC®3719 is a 2-phase, VID programmable, synchro-

nous step-down switching regulator controller that drives

two N-channel external power MOSFET stages in a fixed fre-

quency architecture. The 2-phase controller drives its two

output stages out of phase at frequencies up to 300kHz to

minimize the RMS ripple currents in both input and output

capacitors. The 2-phase technique effectively multiplies the

fundamental frequency by two, improving transient re-

sponse while operating each channel at an optimum fre-

quency for efficiency. Thermal design is also simplified.

An operating mode select pin (FCB) can be used to select

among three modes including Burst Mode® operation for

highest efficiency. An internal differential amplifier provides

true remote sensing of the regulated supply’s positive and

negative output terminals as required in high current ap-

plications.

The RUN/SS pin provides soft-start and optional timed,

short-circuit shutdown. Current foldback limits MOSFET

dissipation during short-circuit conditions when the

overcurrent latchoff is disabled. OPTI-LOOP compensation

allows the transient response to be optimized for a wide

range of output capacitors and ESR values.

TYPICAL APPLICATIO

0.1µF

220pF

3.3k

5 VID BITS

FCB

VIN

TG1

RUN/SS

BOOST1

SW1

LTC3719

ITH

BG1

SGND

PGND

PGOOD

VID0–VID4

SENSE1+

SENSE1–

TG2

EAIN

BOOST2

ATTENOUT

SW2

ATTENIN

BG2

VDIFFOUT

VOS–

VOS+

INTVCC

SENSE2+

SENSE2–

0.47µF

0.47µF

10µF

10µF

35V

×6

1µH

D1

0.002Ω

1µH

D2

0.002Ω

Figure 1. High Current Dual Phase Step-Down Converter

VIN

5V TO 28V

VDD_CORE

0.8V TO 1.55V

45A

+ COUT

270µF

2V

×4

3716 F01

sn3719 3719fs

1

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