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LT3082

200mA Single Resistor Low Dropout Linear Regulator

Linear Technology 

LT3082

APPLICATIONS INFORMATION

Introduction

The LT3082 regulator is easy to use and has all the pro-

tection features expected in high performance regulators.

Included are reverse-input, reverse-output and reverse

input-to-output protection for sensitive circuitry and loads.

Additional protection includes short-circuit protection and

thermal shutdown with hysteresis.

The LT3082 fits well in applications needing multiple rails.

This new architecture adjusts down to zero with a single

resistor, handling modern low voltage digital IC’s as well

as allowing easy parallel operation and thermal manage-

ment without heat sinks. Adjusting to zero output allows

shutting off the powered circuitry. When the input is pre-

regulated—such as a 5V or 3.3V input supply—external

resistors can help spread the heat.

A precision “0” TC 10μA reference current source connects

to the noninverting input of a power operational amplifier.

The power operational amplifier provides a low impedance

buffered output to the voltage on the noninverting input.

A single resistor from the noninverting input to ground

sets the output voltage. If this resistor is set to 0Ω, zero

output voltage results. Therefore, any output voltage be-

tween zero and the maximum defined by the input power

supply voltage is obtainable.

The benefit of using a true internal current source as the

reference, as opposed to a bootstrapped reference in older

regulators, is not so obvious in this architecture. A true

reference current source allows the regulator to have gain

and frequency response independent of the impedance on

the positive input. On older adjustable regulators, such as

the LT1086, loop gain changes with output voltage and

bandwidth changes if the adjustment pin is bypassed

to ground. For the LT3082, loop gain is unchanged with

output voltage changes or bypassing. Output regulation

is not a fixed percentage of output voltage, but is a fixed

fraction of millivolts. Use of a true current source allows

all of the gain in the buffer amplifier to provide regulation,

and none of that gain is needed to amplify up the reference

to a higher output voltage.

Programming Output Voltage

The LT3082 generates a 10μA reference current that

flows out of the SET pin. Connecting a resistor from SET

to GND generates a voltage that becomes the reference

point for the error amplifier (see Figure 1). The reference

voltage equals 10μA multiplied by the value of the SET

pin resistor. Any voltage may be generated and there

is no minimum output voltage for the regulator. Table

1 lists many common output voltages and the closest

standard 1% resistor values used to generate that output

voltage.

Regulation of the output voltage requires a minimum load

current of 0.5mA. For a true 0V output operation, return

this minimum 0.5mA load current to a negative supply

voltage.

IN

CIN

LT3082

10μA

+

–

SET

CSET RSET

OUT

VOUT = 10μA • RSET

COUT RLOAD

3082 F01

Figure 1. Basic Adjustable Regulator

3082f

8

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