POWER MANAGEMENT

1

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SC4431

Shunt Regulator With

Open Collector Output

Description

Revision September 9 ,2003

The SC4431 is a four terminal device for regulating an

isolated power supply with output voltages down to 1.5V.

It is intended to be used as a replacement for three

terminal shunt regulators such as SC431L where the

output voltage is too low for the device to function in

conjunction with an opto-isolator. SC4431 achieves this

by having seperate supply and output pins, allowing the

output to sink current at voltages as low as 0.1V, while

the supply pin still has sufficient voltage for the device to

function. In this way, allowing for a 1.4V drop through an

opto-isolator diode, regulation down to 1.5V out can be

achieved.

The SC4431 shunt regulator is available with three

initial reference voltage accuracies (0.5%, 1.0% and

2.0%) in the space saving 5-lead SOT-23 package. The

three voltage tolerances allow the designer the

opportunity to select the proper cost/tolerance for their

application.

Features

Typical Application Circuit

Applications

Telecom Power Supplies

Opto driver for very low output voltage (1.5V)

isolated power supplies

Battery operated applications

Point of use power supplies

Open Collector output drives Optoisolator with

as little as 1.5V input voltage

Trimmed bandgap design - initial accuracies

to + 0.5%

40mA drive capability

Regulates output as low as 50mV

Wide supply voltage range - 1.5V to 15V

Low supply current - typically 110µA

Full industrial temperature range

SOT-23 5 lead package

2V OUT

R1

U1

4N25

5

OUT

R3

6.34k

C2

22nF

C1

33nF

R2

5.1k

VIN

T1

R4

10k

Primary Side

Controller

Secondary Side

Rectification

and Filtering

SC4431

1

4

VCC

GND

NC

REF

3

2

C3

2V Output Isolated Power Supply