LTM8025

9

8025f

BLOCK DIAGRAM

OPERATION

The LTM8025 is a standalone nonisolated step-down

switching DC/DC power supply that can deliver up to 3A of

output current. This module provides a precisely regulated

output voltage programmable via one external resistor

from 0.8V to 25V. The input voltage range is 3.6V to 36V.

Given that the LTM8025 is a step-down converter, make

sure that the input voltage is high enough to support the

desired output voltage and load current.

As shown in the Block Diagram, the LTM8025 contains a

current mode controller, power switching element, power

inductor, power Schottky diode and a modest amount of

input and output capacitance. The LTM8025 is a fixed

frequency PWM regulator. The switching frequency is set

by simply connecting the appropriate resistor value from

the RT pin to GND.

An internal regulator provides power to the control circuitry.

pin, but if the BIAS pin is connected to an external volt-

age higher than 2.8V, bias power will be drawn from the

external source (typically the regulated output voltage).

This improves efficiency. The RUN/SS pin is used to place

the LTM8025 in shutdown, disconnecting the output and

reducing the input current to less than 1μA.

To further optimize efficiency, the LTM8025 automatically

Between bursts, all circuitry associated with controlling

the output switch is shut down reducing the input supply

current to 50μA in a typical application.

The oscillator reduces the LTM8025’s operating frequency

when the voltage at the ADJ pin is low. This frequency

foldback helps to control the output current during start-

up and overload.

The LTM8025 contains a power good comparator which

trips when the ADJ pin is at roughly 90% of its regulated

value.ThePGOODoutputisanopen-collectortransistorthat

is off when the output is in regulation, allowing an external

resistor to pull the PGOOD pin high. Power good is valid

The LTM8025 is equipped with a thermal shutdown that

will inhibit power switching at high junction tempera-

tures. The activation threshold of this function, however,

is above 125°C to avoid interfering with normal operation.

Thus, prolonged or repetitive operation under a condition

in which the thermal shutdown activates may damage or

impair the reliability of the device.

8025 BD

8.2μH

4.4μF

0.2μF

CURRENT

MODE

CONTROLLER

RUN/SS

SHARE

SYNC

AUX

BIAS

GND

RT

ADJ

PGOOD

15pF

499k

Burst Mode is a registered trademark of Linear Technology Corporation.