LTM8046 datasheet(9/20 Pages) LINER

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LTM8046

8046fb

For more information www.linear.com/LTM8046

block DiagraM

VIN

RUN

*DO NOT ALLOW BIAS VOLTAGE TO EXCEED VIN

GND

0.1µF

1µF

VOUT

CURRENT

MODE

CONTROLLER

VOUT–

BIAS*

8046 BD

•

operaTion

The LTM8046 is a stand-alone isolated flyback switching

DC/DC µModule converter that can deliver over 700mA of

output current. This module provides a regulated output

voltage programmable via one external resistor from 1.8V

to 12V. The input voltage range of the LTM8046 is 3.1V

to 31V. Given that the LTM8046 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.

Asimplifiedblockdiagramisgiven.TheLTM8046contains

acurrentmodecontroller,powerswitchingelement,power

transformer, power Schottky diode, a modest amount of

input and output capacitance.

The LTM8046 has a galvanic primary to secondary isola-

tion rating of 2kVAC. This is verified by applying 3kVDC

between the primary to secondary for 1 second. Note

that the 2kVAC isolation is verified by a 3kVDC test. This

is because the 2kVAC waveform has a peak voltage 1.414

times higher than 2kV, or 2.83kVDC. For the LTM8046, at

least 3kVDC is applied. For further 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

LTM8046, disconnecting the output and reducing the

input current to 1μA or less.

The LTM8046 is a variable frequency device. For a fixed

input and output voltage, the frequency decreases as

the load increases. For light loads, the current through

the internal transformer may be discontinuous, so that

frequency may appear to decrease. Note that a minimum

load is required to keep the output voltage in regulation.

Refer to the Typical Performance Characteristics section.

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