CS3972
CS3972
1.25A High Efficiency Switching Regulator
Description
The CS3972 is a 1.25A, 60V, current
mode, high efficiency, switching
regulator circuit. It can be config-
ured in buck, boost, forward, iso-
lated and non-isolated topologies,
using a single-ended switch.
The IC contains a 1.25A high effi-
ciency output switch, precision
bandgap reference, voltage regula-
tor, error amplifier, oscillator, con-
trol, and protection circuitry.
Output transistor efficiency is
achieved by keeping the switch in
quasi-saturation when it is on. This
minimizes the switch turn-off
delay time and power dissipation,
an important consideration for
applications with wide ranging
loads.
The precision reference is internally
trimmed to 1.24V, while the oscilla-
tor frequency is internally trimmed
to 40kHz. The on board 2.3V regu-
lator powers the internal circuitry.
By keeping the voltage regulator at
2.3V, the IC is able to operate down
to 3V and maintain a constant input
supply current of 6mA(typ).
Synchronization mode is achieved
by applying a pulsating V
C
voltage
of less than 0.2V with a duration of
about 0.5µs to V
C
pin. The switch-
ing frequency can be adjusted from
50kHz to 70kHz. The IC's synchro-
nization mode is set externally.
Protection circuitry includes a vari-
able current limit with external
voltage clamp, under-voltage and
over-temperature protection.
Features
s
75V
MAX
, 2A
PEAK
Internal
Switch
s
3V to 60V Input Voltage
Range
s
6mA Input Supply
Current
s
1.24V Precision Reference
s
40kHz Switching
Frequency
s
Variable Current Limit
with External Voltage
Clamp
s
Under-Voltage Protection
s
Over-Temperature
Protection
s
External Synchronization
Package Options
Block Diagram
NC
V
C
V
FB
VSW
VIN
2.3V
Reg
Output
Protection
1
16L SO Wide
Gnd
NC
E
2
V
SW
NC
E
1
NC
V
IN
NC
NC
NC
40kHz
OSC
Logic
Driver
1.25A,
75V
Switch
NC
NC
+
VC
COMP
-
Gnd
1
8L PDIP
E
2
V
SW
E
1
V
IN
5L TO-220
Tab (Gnd)
VFB
-
Error
Amp
+
1.24V
Ref
V
C
+
Current
Amp
-
0.22Ω
0.22Ω
E2*
E1 *
Gnd
V
FB
NC
1 V
C
2 V
FB
3 Gnd
4 V
SW
5 V
IN
1
*Always connect E1 to Ground Pin on DIP package. Both emitters are tied to ground on TO-220 Package.
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
Rev. 6/23/99
1
A
®
Company
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
