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LTM8048

8048fa

OPERATION

The LTM8048 is a stand-alone isolated flyback switching

DC/DC power supply that can deliver up to 440mA of

output current. This module provides a regulated output

voltage programmable via one external resistor from 2.5V

to 13V. It is also equipped with a high performance linear

post regulator. The input voltage range of the LTM8048 is

3.1V to 32V. Given that the LTM8048 is a flyback converter,

the output current depends upon the input and output

voltages, so make sure that the input voltage is high

enough to support the desired output voltage and load

current. The Typical Performance Characteristics section

gives several graphs of the maximum load versus VIN for

several output voltages.

A simplified block diagram is given. The LTM8048 contains

a current mode controller, power switching element, power

transformer, power Schottky diode, a modest amount of

input and output capacitance and a high performance

linear post regulator.

The LTM8048 has a galvanic primary to secondary isola-

tion rating of 725VDC. This is verified by applying 725VDC

between the primary to secondary for 1 second and then

applying –725VDC for 1 second. For details please refer

to the Isolation and Working Voltage section.

An internal regulator provides power to the control cir-

cuitry. The bias regulator normally draws power from the

VIN pin, but if the BIAS pin is connected to an external

voltage higher than 3.1V, bias power will be drawn from

the external source, improving efficiency. VBIAS must not

exceed VIN. The RUN pin is used to turn on or off the

LTM8048, disconnecting the output and reducing the input

current to 1μA or less.

The LTM8048 is a variable frequency device. For a fixed

input and output voltage, the frequency increases as the

load increases. For light loads, the current through the

internal transformer may be discontinuous.

The post regulator is a high performance 300mA low

dropout regulator with micropower quiescent current and

shutdown. The device is capable of supplying 300mA at

a dropout voltage of 300mV. Output voltage noise can be

lowered to 20μVRMS over a 100Hz to 100kHz bandwidth

with the addition of a 0.01μF reference bypass capacitor.

Additionally, this reference bypass capacitor will improve

transient response of the regulator, lowering the settling

time for transient load conditions. The linear regulator is

protected against both reverse input and reverse output

voltages.

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