CS3842B/CS3843B
Off-Line Current Mode PWM
Control Circuit
with Very Low Start Up Current
Description
Features
The CS384XB provides all the neces-
possible. On board logic ensures that
V is stabilized before the output
REF
stage is enabled. Ion-implant resistors
provide tighter control of undervoltage
lockout.
ꢀ Very low Start Up Current
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).
(300µA typ)
Optimized Off-line
Control
ꢀ
ꢀ
Internally Trimmed,
Temperature
Compensated Oscillator
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.
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
Maximum Duty-cycle
Clamp
ꢀ
ꢀ VREF stabilization before
Output Enable
These ICs are available in 8 and 14 lead
surface mount (SO) and 8 lead PDIP
packages.
ꢀ Pulse-by-pulse Current
Limiting
ꢀ Improved Undervoltage
Absolute Maximum Ratings
Lockout
Supply Voltage (ICC<30mA)..........................................................Self Limiting
Supply Voltage (Low Impedance Source)...................................................30V
Output Current ...............................................................................................±1A
Output Energy (Capacitive Load) .................................................................5µJ
Analog Inputs (VFB, Sense) ............................................................-0.3V to 5.5V
Error Amp Output Sink Current...............................................................10mA
Lead Temperature Soldering
ꢀ Double Pulse Suppression
ꢀ 1% Trimmed Bandgap
Reference
ꢀ High Current Totem Pole
Output
Package Options
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
8 Lead PDIP & SO Narrow
Block Diagram
1
2
3
4
8
7
6
5
COMP
VFB
VREF
VCC
VCC
VCC Pwr
Undervoltage
Lock-out Circuit
Sense
OSC
VOUT
Gnd
34V
Set/
5V
VREF
Reset Reference
Gnd
16V/10V
(8.4V/7.6V)
Internal
Bias
14L SO Narrow
REF
2.50V
Output
Enable
OSC
NOR
1
2
3
4
5
6
7
14
13
12
11
10
9
Oscillator
COMP
NC
VREF
NC
VOUT
S
R
2 R
+
–
VFB
VCC
PWM
Latch
VFB
VC
Error
Pwr Gnd
NC
VCC Pwr
VOUT
R
Amplifier
Current
Sense
Comparator
1 V
COMP
Sense
Sense
NC
Pwr Gnd
Gnd
( ) Indicates CS-3843B
8
OSC
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
June, 1999 - Rev. 3
1
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