SLUS188A – APRIL 1997 – REVISED FEBRUARY 2007
Power Supply Supervisory Circuit
• Includes Over-Voltage, Under-Voltage, and
Current Sensing Circuits
• Internal 1% Accurate Reference
• Programmable Time Delays
• SCR “Crowbar” Drive of 300 mA
• Remote Activation Capability
• Optional Over-Voltage Latch
• Uncommitted Comparator Inputs for Low
Voltage Sensing (UC1544 Series Only)
The monolithic integrated circuits contain all the
functions necessary to monitor and control the output
of a sophisticated power supply system.
Over-voltage (O.V.) sensing with provision to trigger
an external SCR “crowbar” shutdown; an
undervoltage (U.V.) circuit which can be used to
monitor either the output or to sample the input line
voltage; and a third op amp/comparator usable for
current sensing (C.L.) are all included in this device,
together with an independent, accurate reference
Both over- and under-voltage sensing circuits can be
externally programmed for minimum time duration of
fault before triggering. All functions contain open
collector outputs which can be used independently or
wire-or’ed together, and although the SCR trigger is
directly connected only to the over-voltage sensing
circuit, it may be optionally activated by any of the
other outputs, or from an external signal. The O.V.
circuit also includes an optional latch and external
The UC1544/2544/3544 devices have the added
versatility of completely uncommitted inputs to the
voltage sensing comparators so that levels less than
2.5 V may be monitored by dividing down the internal
reference voltage. The current sense circuit may be
used with external compensation as a linear amplifier
or as a highgain comparator. Although nominally set
for zero input offset, a fixed threshold may be added
with an external resistor. Instead of current limiting,
this circuit may also be used as an additional voltage
The reference generator circuit is internally trimmed
to eliminate the need for external potentiometers and
the entire circuit may be powered directly from either
the output being monitored or from a separate bias
For each terminal, first number refers to 1543 series, second to 1544 series.
*On 1543 series, this function is internally connected to VREF.
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PRODUCTION DATA information is current as of publication date.
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