Datasheet

UC1901
UC2901
UC3901
Isolated Feedback Generator
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 associ-
ated 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 er-
ror 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 switch-
ing frequency of a SMPS.
An additional feature is a status monitoring circuit which provides an active-
low 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.
µ µ
µ
UC1901 SIMPLIFIED SCHEMATICNovember S
SLUS279A - November 1998 - Revised January 2010
UDG-98080