1
Output
Protection
Driver
2.3V
Reg
Logic
40kHz
OSC
Error
Amp
-
+
1.24V
Ref
Current
Amp
-
+
VSW
VC
VIN
VFB
0.22
COMP
E1*
E2*
Gnd
*Always connect E1 to Ground Pin on DIP package. Both emitters are tied to ground on TO-220 Package.
1.25A,
75V
Switch
-
+
CS3972
1.25A High Efficiency Switching Regulator
CS3972
Description
Block Diagram
Features
s
75VMAX, 2APEAK 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
5L TO-220
Tab (Gnd)
8L PDIP
1
Gnd
VC
VFB
NC
E2
VSW
E1
VIN
1
1VC
2VFB
3 Gnd
4VSW
5VIN
16L SO Wide
1
Gnd
NC
VIN
E1
VSW
E2
VC
VFB
NC
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 VC voltage
of less than 0.2V with a duration of
about 0.5s to VC 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.
Rev. 6/23/99
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
A
Company