1FEATURES

? Ideal for Multiple Output and/or High

Voltage Output Voltage Converters

? Up to 500 kHz Operation

? High Voltage, High Current Floating

Driver for Buck Converter Stage

? UC3827-1 Current Fed Controller has

Push-Pull Drivers with Overlapping

Conduction Periods

? UC3827-2 Voltage Fed Controller has

Push-Pull Drivers with Nonoverlapping

Conduction Periods

? Average Current Mode, Peak Current

Mode or Voltage Mode with Input

Voltage Feedforward Control for Buck

Power Stage

? Wide Bandwidth, Low Offset,

Differential Current Sense Amplifier

? Precise Short Circuit Current Control

DESCRIPTION

The UC3827 family of controller devices provides an

integrated control solution for cascaded buck and

push-pull converters. These converters are known as

current fed or voltage fed push-pull converters and

are ideally suited for multiple output and/or high

voltage output applications. In both current fed and

voltage fed modes, the push-pull switches are driven

at 50% nominal duty cycles and at one half the

switching frequency of the buck stage. In the current

fed mode, the two switches are driven with a

specified over-lap period to prevent ringing and

voltage stress on the devices. In the voltage fed

mode, the two switches are driven with a specified

gap time between the switches to prevent shorting

the transformer across the energy storage capacitor

and to prohibit excessive currents flowing through the devices.

The converter's output voltage is regulated by pulse

width modulation of the buck switch. The UC3827

contains complete protection and PWM control

functions for the buck converter. Easy control of the

floating switch is accomplished by the floating drive

circuitry. The gate drive waveform is level shifted to

support an input voltage up to 72 VDC.