Document
UC2827-1, UC2827-2 UC3827-1, UC3827-2
www.ti.com
SLUS365D – APRIL 1999 – REVISED APRIL 2011
BUCK CURRENT/VOLTAGE FED PUSH-PULL PWM CONTROLLERS
Check for Samples: UC2827-1, UC2827-2, UC3827-1, UC3827-2
FEATURES
1
• 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.
BLOCK DIAGRAM
VEAOCEA+ CEAO
10
Voltage Error Amplifier
VEA+ 14
12
6
VEA− 16
Current Error Amplifier
CEA− 13
CSAO 7 CSA+ 8 CSA− 9
SS 4 SYNC 19
CT 18 RT 17
+3 V
ILIM Comparator
Current Sense Amplifier
OSC
SS INHBT
UV
500 kHz MAX
REF 15
+
RAMP
5
0.7 V PWM Comparator
RD SQ
OSC
Q DELAY T
Q
VCC 23 GND 11
REF &
UVLO UVLO
DELAY
Flying Driver
Push/Pull Drivers
20
DELAY
1 V+ 2 BUCK 3 SRC 21 PGND
24 PUSH 22 PULL
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Copyright © 1999–2011, Texas Instruments Incorporated
UC2827-1, UC2827-2 UC3827-1, UC3827-2
SLUS365D – APRIL 1999 – REVISED.