FEATURES DESCRIPTION
R
D
QS
20
DELAY
23
GND
11
VCC
REF
15
RT
17
CT
18
SYNC
19
CSA−
9
CSA+
8
SS
4
CSAO
7
CEA−
13
VEA−
16
VEA+
14
22
24
3
2
1
RAMPCEA+
12
CEAOVEAO
10
PULL
PGND
PUSH
SRC
BUCK
V+
DELAY
DELAY
T
Q
Q
REF
&
UVLO
SS
INHBT
UV
OSC
500 kHz
MAX
6 5
21
Current Sense
Amplifier
ILIM Comparator
+3 V
Current Error
Amplifier
PWM Comparator0.7 V
Flying
Driver
Push/Pull
Drivers
OSC
UVLO
Voltage Error
Amplifier
+
UC1827-1, UC1827-2
UC2827-1, UC2827-2
UC3827-1, UC3827-2
SLUS365A – APRIL 1999 – REVISED AUGUST 2005
BUCK CURRENT/VOLTAGE FED PUSH-PULL
PWM CONTROLLERS
• Ideal for Multiple Output and/or High
The UC3827 family of controller devices provides an
Voltage Output Voltage Converters
integrated control solution for cascaded buck and
push-pull converters. These converters are known as
• Up to 500 kHz Operation
current fed or voltage fed push-pull converters and
• High Voltage, High Current Floating
are ideally suited for multiple output and/or high
Driver for Buck Converter Stage
voltage output applications. In both current fed and
• UC3827-1 Current Fed Controller has
voltage fed modes, the push-pull switches are driven
Push-Pull Drivers with Overlapping
at 50% nominal duty cycles and at one half the
switching frequency of the buck stage. In the current
Conduction Periods
fed mode, the two switches are driven with a speci-
• UC3827-2 Voltage Fed Controller has
fied over-lap period to prevent ringing and voltage
Push-Pull Drivers with Nonoverlapping
stress on the devices. In the voltage fed mode, the
Conduction Periods
two switches are driven with a specified gap time
• Average Current Mode, Peak Current
between the switches to prevent shorting the trans-
Mode or Voltage Mode with Input
former across the energy storage capacitor and to
prohibit excessive currents flowing through the de-
Voltage Feedforward Control for Buck
vices.
Power Stage
• Wide Bandwidth, Low Offset,
The converter's output voltage is regulated by pulse
Differential Current Sense Amplifier
width modulation of the buck switch. The UC3827
contains complete protection and PWM control func-
• Precise Short Circuit Current Control
tions 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 V
DC
.
BLOCK DIAGRAM
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.
Copyright © 1999–2005, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
