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Simple Single Inductor Buck
PWM Stepdown Voltage
Regulation
Drives External PMOS Switch
Contains UVLO Circuit
Includes Pulse-by-Pulse Current
Limit
Low 50碌A Sleep Mode Current
DESCRIPTION
The UC3573 is a Buck pulse width modulator which steps down and regu-
lates a positive input voltage. The chip is optimized for use in a single
inductor buck switching converter employing an external PMOS switch.
The block diagram consists of a precision reference, an error amplifier
configured for voltage mode operation, an oscillator, a PWM comparator
with latching logic, and a 0.5A peak gate driver. The UC3573 includes an
undervoltage lockout circuit to insure sufficient input supply voltage is pre-
sent before any switching activity can occur, and a pulse-by-pulse current
limit. Input current can be sensed and limited to a user determined maxi-
mum value. In addition, a sleep comparator interfaces to the UVLO circuit
which turns the chip off when the input voltage is below the UVLO thresh-
old. This reduces the supply current to only 50碌A, making the UC3573
ideal for battery powered applications.
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BLOCK DIAGRAM
UDG-94106-1
9/96
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