CAT102
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
VOUT at 0.3V. The wide input supply range allows the
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.
The current limit can be adjusted by using a resistor R3
connected between the IN and OUT pins. For example,
a 3.3V supply VIN is associated with R3 = 135Ω, and a
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 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:
VOUT = (1 + R1/R2) x 0.6V
Figure 1. Application circuits for 0.6V output and 1.2V output voltages
R
3
V
IN
V
OUT
3.3V
0.6V/20mA
5
2
3
1
IN
OUT
FB
C
C
2
1
CAT102
0.1µF
1µF
GND
R
3
V
IN
V
= (1 + R /R ) x 0.6V
1 2
OUT
3.3V
1.2V/20mA
5
2
3
1
IN
OUT
FB
C
C
2
1
R
1
CAT102
0.1µF
1µF
10kꢀ
GND
R
2
10kꢀ
Doc. No. MD-4007 Rev. N
4
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CATALYST [ CATALYST SEMICONDUCTOR ]
