CS51221
CS51221
Enhanced Voltage Mode PWM Controller
Description
The CS51221 fixed frequency
feed forward voltage mode
PWM controller contains all of
the features necessary for basic
voltage mode operation. This
PWM controller has been opti-
mized for high frequency prima-
ry side control operation. In
addition, this device includes
such features as: Soft Start, accu-
rate duty cycle limit control, less
than 50µA startup current, over
and under voltage protection,
and bidirectional synchroniza-
tion. The CS51221 is available in
16 lead PDIP and SO narrow
surface mount packages.
s
s
Features
1MHz Frequency Capability
Fixed Frequency Voltage
Mode Operation, with Feed
Forward
Thermal Shutdown
Under Voltage Lock-out
Accurate Programmable Max
Duty Cycle Limit
1A Sink/Source Gate Drive
Programmable Pulse by
Pulse Over Current
Protection
Leading Edge Current Sense
Blanking
75ns Shutdown Propagation
Delay
Programmable Soft Start
Under Voltage Protection
Over Voltage Protection with
Programmable Hysteresis
Bidirectional
Synchronization
25ns GATE Rise and Fall
Time (1nF load)
3.3V 3% Reference Voltage
Output
s
s
s
s
s
s
s
Application Diagram
36V-72V to 5V/5A converter
s
s
s
s
s
BAS21
V
IN
(36V to 72V)
51k
FZT688
11V
10
100
1µF
22µF
18V
160k
T3
100:1
0.1µF
24.3k
V
C
V
REF
V
CC
UV
OV
I
SET
FF
GATE
I
SENSE
U1
s
T2
2:5
V
OUT
(5V/5A)
100µF
SGnd
510k
10k
T1
4:1
MBRB2545CT
10
CS51221/2
0.22µF
10k
1µF
SYNC
330pF
0.01µF
200
2200pF
4.3k
D11
BAS21
100pF
COMP
V
FB
R
T
/C
T
SYNC
SS
LGnd
680pF
D13
V33MLA1206A23
20.25k
13k
10
IRF634
Package Options
16 Lead SO Narrow & PDIP
GATE
I
SENSE
1
PGnd
470pF
62
10
VC
PGnd
V
CC
V
REF
LGnd
SS
COMP
V
FB
0.1µF 5.1k
SYNC
2k
5.6k
180
1k
TL431
2k
150
4700pF
MOC81025
FF
UV
OV
R
T
C
T
I
SET
1k
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. 3/26/99
1
A
®
Company