CS3842B/3843B
CS3842B/CS3843B
Off-Line Current Mode PWM Control Circuit
with Very Low Start Up Current
Description
The CS384XB provides all the neces-
sary features to implement off-line
fixed frequency current-mode control
with a minimum number of external
components. The family has been opti-
mized for very low start up current
(300µA, typ).
The CS384XB family incorporates a
precision temperature-controlled oscil-
lator with an internally trimmed dis-
charge current to minimize variations
in frequency. A precision duty-cycle
clamp eliminates the need for an exter-
nal oscillator when a 50% duty-cycle is
used. Duty-cycles of almost 100% are
possible. On board logic ensures that
VREF is stabilized before the output
stage is enabled. Ion-implant resistors
provide tighter control of undervoltage
lockout.
Other features include pulse-by-pulse
current limiting, and a high-current
totem pole output for driving capaci-
tive loads, such as the gate of a power
MOSFET. The output is LOW in the off
state, consistent with N-channel
devices.
These ICs are available in 8 and 14 lead
surface mount (SO) and 8 lead PDIP
packages.
Features
s
Very low Start Up Current
(300µA typ)
s
Optimized Off-line
Control
s
Internally Trimmed,
Temperature
Compensated Oscillator
s
Maximum Duty-cycle
Clamp
s
V
REF
stabilization before
Output Enable
s
Pulse-by-pulse Current
Limiting
s
Improved Undervoltage
Lockout
s
Double Pulse Suppression
s
1% Trimmed Bandgap
Reference
s
High Current Totem Pole
Output
Absolute Maximum Ratings
Supply Voltage (I
CC
<30mA) ..........................................................Self Limiting
Supply Voltage (Low Impedance Source)...................................................30V
Output Current ...............................................................................................±1A
Output Energy (Capacitive Load) .................................................................5µJ
Analog Inputs (V
FB
, Sense) ............................................................-0.3V to 5.5V
Error Amp Output Sink Current...............................................................10mA
Lead Temperature Soldering
Wave Solder (through hole styles only) ...................10 sec. max, 260°C peak
Reflow (SMD styles only) ....................60 sec. max above 183°C, 230°C peak
Block Diagram
V
CC
Undervoltage
Lock-out Circuit
34V
Gnd
16V/10V
(8.4V/7.6V)
REF 2.50V
OSC
Output
Enable
NOR
V
OUT
+
V
FB
Error
Amplifier
COMP
Sense
( ) Indicates CS-3843B
–
V
C
R
1 V
2 R
S
R
Current
Sense
Comparator
PWM
Latch
Set/
5V
Reset Reference
Internal
Bias
V
REF
V
CC
Pwr
Package Options
8 Lead PDIP & SO Narrow
COMP
V
FB
Sense
OSC
1
2
3
4
8
7
6
5
V
REF
V
CC
V
OUT
Gnd
14L SO Narrow
COMP
1
NC
2
V
FB
3
NC
4
Pwr Gnd
14
13
12
11
10
9
8
V
REF
NC
V
CC
V
CC
Pwr
V
OUT
Pwr Gnd
Gnd
Oscillator
Sense
5
NC
6
OSC
7
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 ]
