FEATURES

? Simple Single Inductor Flyback PWM

for Negative Voltage Generation

? Drives External PMOS Switch

? Contains UVLO Circuit

? Includes Pulse-by-Pulse Current Limit

? Low 50μA Sleep Mode Current

DESCRIPTION

The UC3572 is a negative output flyback pulse width modulator which converts

a positive input voltage to a regulated negative output voltage. The

chip is optimized for use in a single inductor negative flyback 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 UC3572 includes an undervoltage lockout circuit to insure

sufficient input supply voltage is present before any switching activity can

occur, and a pulse-by-pulse current limit. Output current can be sensed and

limited to a user determined maximum value. The UVLO circuit turns the

chip off when the input voltage is below the UVLO threshold. In addition, a

sleep comparator interfaces to the UVLO circuit to turn the chip off. This reduces

the supply current to only 50μA, making the UC3572 ideal for battery

powered applications.