CS3972 Datasheet, PDF (1/6 Pages) Cherry Semiconductor Corporation – 1.25A High Efficiency Switching Regulator

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.
Block Diagram
VIN
2.3V
Reg
40kHz
OSC
Logic
Output
Protection
Driver
VSW
1.25A,
75V
Switch
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
16L SO Wide
NC 1
V_C
V_FB
NC
NC
NC
NC
NC
Gnd
NC
E₂
V_SW
NC
E₁
NC
V_IN
COMP
+
-
VC
VFB
-
Error
Amp
+
1.24V
Ref
+
Current
Amp
-
0.22Ω
0.22Ω
*Always connect E1 to Ground Pin on DIP package. Both emitters are tied to ground on TO-220 Package.
Rev. 6/23/99
1
8L PDIP
5L TO-220
Tab (Gnd)
E2*
E1*
Gnd
Gnd 1
V_C
V_FB
NC
E₂
V_SW
E₁
V_IN
1
1 V_C
2 V_FB
3 Gnd
4 V_SW
5 V_IN
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: [phone] Fax: [phone]
Email: [e-mail]
Web Site: www.cherry-semi.com
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Company
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