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.