CS3842B Datasheet, PDF (1/8 Pages) Cherry Semiconductor Corporation – Off-Line Current Mode PWM Control Circuit Off-Line Current Mode PWM Control Circuit

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.
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
Gnd
OSC
V_FB
COMP
Sense
Undervoltage
Lock-out Circuit
34V
Set/
5V
Reset Reference
16V/10V
(8.4V/7.6V)
REF 2.50V
Output
Enable
Oscillator
Internal
Bias
NOR
+
–
Error
V_C
Amplifier
2R
R
S
R
1 V Current
Sense
Comparator
PWM
Latch
( ) Indicates CS-3843B
V_CC Pwr
V_REF
V _{O UT}
Pwr Gnd
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
Package Options
8 Lead PDIP & SO Narrow
COMP 1
V_FB 2
Sense 3
OSC 4
8 V_REF
7 V_CC
6 V_OUT
5 Gnd
14L SO Narrow
COMP 1
NC 2
V_FB 3
NC 4
Sense 5
NC 6
OSC 7
14 V_REF
13 NC
12 V_CC
11 V_CC Pwr
10 V_OUT
9 Pwr Gnd
8 Gnd
December, 2001 - Rev. 4
ON Semiconductor
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885–3600 Fax: (401)885–5786
N. American Technical Support: 800-282-9855
Web Site: www.cherry–semi.com
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