application
INFO
UC2578
UC3578
available
Buck Pulse Width Modulator Stepdown Voltage Regulator
FEATURES
DESCRIPTION
• Provides Simple Single Inductor Buck The UC3578 is a PWM controller with an integrated high side floating gate
PWM Step-Down Voltage Regulation
driver. It is used in buck step down converters and regulates a positive
output voltage. Intended to be used in a distributed power system, the IC
allows operation from 14V to 72V input voltage which range includes the
prevalent telecomm bus voltages. The output duty cycle of the UC3578
can vary between 0% and 90% for operation over the wide input voltage
and load conditions.
• Drives External High Side NMOS
Switch
• 14V to 72V Input Voltage Operating
Range
• Contains 100kHz Internal Oscillator,
2V Reference and UVLO
The UC3578 simplifies the design of the single switch PWM buck converter
by incorporating a floating high side driver for an external N-channel
MOSFET switch. It also features a 100kHz fixed frequency oscillator, an
internal 2V precision reference, an error amplifier configured for voltage
mode operation, and a PWM comparator with latching logic. Comple-
menting the traditional voltage mode control block, the UC3578 incorpo-
rates an overcurrent shutdown circuit with full cycle soft re-start to limit the
input current to a user defined maximum value during overload operation.
Additional functions include an under voltage lockout circuit to insure that
sufficient input supply voltage is present before any switching activity can
occur.
• Soft Start on Power Up
• Overcurrent Shutdown Followed by
Soft Start
The UC2578 and the UC3578 are both available in surface mount and
thru-hole power packages.
ORDERING INFORMATION
TEMPERATURE RANGE
PACKAGE
Power SOIC
Power PDIP
Power SOIC
Power PDIP
UC2578DP
UC2578N
UC3578DP
UC3578N
–40°C to +85°C
0°C to +70°C
TYPICAL APPLICATION DIAGRAM
R
L
SENSE
0.12
OUT
15-40 V
V
IN
OUT
IRFZ34
40µH
C
S
R
1k
S
C
220µF
1µF
1000pF
OUT
RECTIFIER
MBR 3100
15
C
GG
1µF
47µF
1N4148
5k
11
DIODE CS
14 VCC
15
10
7
6
10
C
VGG OUT
SRC
EAINV
2
50k
R1
220pF
CC
UC3578
1µF
2200pF
100k
16 SS
GND GND GND GND
EAOUT
3
1k
4
5
12
13
C
SS
UDG-99064
05/99