LTM4657 datasheet(9/28 Pages) AD

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LTM4657

Rev. A

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OPERATION

The LTM4657 is a standalone nonisolated switch mode

DC/DC power supply. It can deliver up to 8A DC output

current with few external input and output capacitors.

This module provides precisely regulated output voltage

adjustable between 0.5V to 5.5V via one external resistor

over a 3.1V to 20V input voltage range. The typical appli-

cation schematic is shown in Figure 23.

The LTM4657 contains an integrated constant on-time

valley current mode regulator, power MOSFETs, inductor,

and other supporting discrete components. The default

switching frequency is 500kHz. For switching noise-sensi-

tive applications, the switching frequency can be adjusted

by external resistors and the μModule regulator can be

externally synchronized to a clock within ±30% of the set

frequency. See the Applications Information section.

With current mode control and internal feedback loop

compensation, the LTM4657 module has sufficient sta-

bility margins and good transient performance with a

wide range of output capacitors, even with all ceramic

output capacitors.

Current mode control provides cycle-by-cycle fast current

limiting. Internal output overvoltage and undervoltage

comparators pull the open-drain PGOOD output low if the

output feedback voltage exits a ±8% window around the

regulation point. Continuous operation is forced during

OV and UV condition except during start-up when the

TRACK pin is ramping up to 0.5V.

Furthermore, in order to protect the internal power

MOSFET devices against transient voltage spikes, the

LTM4657 constantly monitors the VIN pin for an over-

voltage condition. When VIN rises above 24.5V, the reg-

ulator suspends operation by shutting off both power

MOSFETs. Once VIN drops below 21.5V, the regulator

immediately resumes normal operation. The regulator

does not execute its soft-start function when exiting an

overvoltage condition.

Multiphase operation can be easily employed with the

synchronization and phase mode controls. Up to 6 phases

can be cascaded to run simultaneously with respect to

each other by programming the PHMODE pin to different

levels. The LTM4657 has MODE/CLKIN and CLKOUT pins

for PolyPhase operation of multiple devices or frequency

synchronization.

Pulling the RUN pin to GND forces the controller into its

shutdown state, turning off both power MOSFETs and

most of the internal control circuitry. At light load currents,

discontinuous mode (DCM) operation can be enabled to

achieve higher efficiency compared to continuous mode

(CCM) by pulling the MODE/CLKIN pin to GND. The

TRACK/SS pin is used for power supply tracking

and soft-start programming. See the Applications

Information section.

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