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LTM4600

4600fd

For more information www.linear.com/LTM4600

µModule Description

The LTM4600 is a standalone non-isolated synchronous

switching DC/DC power supply. It can deliver up to 10A of

DC output current with only bulk external input and output

capacitors. This module provides a precisely regulated

outputvoltageprogrammableviaoneexternalresistorfrom

0.6VDC to 5.0VDC, not to exceed 80% of the input voltage.

The input voltage range is 4.5V to 20V. A simplified block

diagram is shown in Figure 1 and the typical application

schematic is shown in Figure 18.

TheLTM4600containsanintegratedLTCconstanton-time

current-mode regulator, ultra-low RDS(ON) FETs with fast

switchingspeedandintegratedSchottkydiode.Thetypical

switching frequency is 850kHz at full load. With current

mode control and internal feedback loop compensation,

the LTM4600 module has sufficient stability margins and

good transient performance under a wide range of operat-

ing conditions and with a wide range of output capacitors,

even all ceramic output capacitors (X5R or X7R).

Current mode control provides cycle-by-cycle fast current

limit. In addition, foldback current limiting is provided in

an over-current condition while VOSET drops. Also, the

LTM4600 has defeatable short circuit latch off. Internal

overvoltage and undervoltage comparators pull the open-

drainPGOODoutputlowiftheoutputfeedbackvoltageexits

a ±10% window around the regulation point. Furthermore,

in an overvoltage condition, internal top FET Q1 is turned

off and bottom FET Q2 is turned on and held on until the

overvoltage condition clears.

Pulling the RUN/SS pin low forces the controller into its

shutdown state, turning off both Q1 and Q2. Releasing the

pin allows an internal 1.2µA current source to charge up

the soft-start capacitor. When this voltage reaches 1.5V,

the controller turns on and begins switching.

At low load current the module works in continuous cur-

rent mode by default to achieve minimum output voltage

ripple. It can be programmed to operate in discontinuous

current mode for improved light load efficiency when the

FCB pin is pulled up above 0.8V and no higher than 6V.

The FCB pin has a 4.75k resistor to ground, so a resistor

to VIN can set the voltage on the FCB pin.

When EXTVCC pin is grounded or open, an integrated 5V

linear regulator powers the controller and MOSFET gate

drivers. If a minimum 4.7V external bias supply is ap-

plied on the EXTVCC pin, the internal regulator is turned

off, and an internal switch connects EXTVCC to the gate

driver voltage. This eliminates the linear regulator power

loss with high input voltage, reducing the thermal stress

on the controller. The maximum voltage on EXTVCC pin is

6V. The EXTVCC voltage should never be higher than the

VIN voltage. Also EXTVCC must be sequenced after VIN.

operaTion

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