FEATURES

· An Amplitude-Modulation System for

Transformer Coupling an Isolated

Feedback Error Signal

· Low-Cost Alternative to Optical

Couplers

· Internal 1% Reference and Error

Amplifier

· Internal Carrier Oscillator Usable to

5MHz

· Modulator Synchronizable to an

External Clock

· Loop Status Monitor

DESCRIPTION

The UC1901 family is designed to solve many of the problems associated

with closing a feedback control loop across a voltage isolation

boundary. As a stable and reliable alternative to an optical coupler, these

devices feature an amplitude modulation system which allows a loop error

signal to be coupled with a small RF transformer or capacitor.

The programmable, high-frequency oscillator within the UC1901 series

permits the use of smaller, less expensive transformers which can readily

be built to meet the isolation requirements of today's line-operated power

systems. As an alternative to RF operation, the external clock input to

these devices allows synchronization to a system clock or to the switching

frequency of a SMPS.

An additional feature is a status monitoring circuit which provides an activelow

output when the sensed error voltage is within ±10% of the reference.

The DRIVERA output, DRIVERB output, and STATUS output are disabled

until the input supply has reached a sufficient level to allow proper operation

of the device.

Since these devices can also be used as a DC driver for optical couplers,

the benefits of 4.5 to 40V supply operation, a 1% accurate reference, and a

high gain general purpose amplifier offer advantages even though an AC

system may not be desired.