CAT102

© 2007 Catalyst Semiconductor, Inc.

5

Doc. No. 4007 Rev. M

Characteristics subject to change without notice

APPLICATIONS INFORMATION

The CAT102 adjustable shunt regulator features

isolated supply inputs and outputs, ideal for isolated

power-supply applications using an optocoupler in

the feedback path. The CAT102 sinks 20mA with

device to operate from 2.2V to 18V. The CAT102

compares the FB input to a precision 600mV

reference. If the FB input is low, the OUT pin sinks

no current. If FB rises above 600mV, the OUT pin

sinks up to 20mA.

Figure 1 shows the CAT102 configured as a shunt

regulator. To generate an output voltage of 0.6V, the

FB pin has to be directly connected to the OUT pin.

A 1.0µF capacitor from OUT to GND is recommen-

ded when the output voltage is 0.6V. A resistor-

divider connected from OUT to GND is used to

produce a higher output voltage as set by the

following equation:

The current limit can be adjusted by using a resistor R3

connected between the IN and OUT pins. For example,

10V supply works best with R3 = 470Ω. The CAT102

shunt regulator is limited to low-current applications with

the OUT pin capable of sinking up to 20mA max.

Figure 1. Application circuits for 0.6V output and 1.2V output voltages

CAT102

IN

GND

3.3V

0.6V/20mA

0.1µF

1µF

OUT

FB

3

1

5

2

3

1

5

2

CAT102

IN

GND

3.3V

1.2V/20mA

0.1µF

1µF

OUT

FB

10kΩ

10kΩ