CS3845B Datasheet, PDF (1/6 Pages) Cherry Semiconductor Corporation – Current Mode PWM Control Circuit with 50% Max Duty Cycle

CS3845B
Current Mode PWM Control Circuit
with 50% Max Duty Cycle
Description
The CS3845B provides all the neces-
sary features to implement off-line
fixed frequency current-mode control
with a minimum number of external
components.
The CS3845B incorporates a precision
temperature-controlled oscillator to
minimize variations in frequency. An
internal toggle flip-flop, which blanks
the output off every other clock cycle,
ensures that the duty-cycle never
exceeds 50%. The undervoltage lock-
out feature ensures that VREF is stabi-
lized within specification before the
output stage is enabled. The CS3845B
has been optimized for lower start up
current (500µA max).
Other features include 1% trimmed
band gap reference, pulse-by-pulse
current limiting, and a high-current
totem pole output for driving capaci-
tive loads.
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, V_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
Features
s Optimized for Off-line Use
s Temperature
Compensated Oscillator
s 50% Maximum Duty-cycle
Clamp
s Low Start-up Current
(500µA max)
s Pulse-by-pulse Current
Limiting
s Undervoltage Active Pull
Down
s Double Pulse Suppression
s 1% Trimmed Bandgap
Reference
s High Current Totem Pole
Output
Package Options
8 Lead PDIP & SO
V_CC
Gnd
V_FB
COMP
OSC
Sense
V_CC Undervoltage Lock-out
34V
8.4V/7.6V
Error
Amplifier
2.50V
Oscillator
Set/ 5.0 Volt
Reset Reference
R
V_REF
Undervoltage
Lockout
R
Toggle
Flip-Flop
NOR
2R
R
S
R
1V
Current PWM
Sensing Latch
Comparator
Internal
Bias
V_CC Pwr
V_REF
V_OUT
Pwr Gnd
COMP 1
V_FB 2
Sense 3
OSC 4
8 V_REF
7 V_CC
6 V_OUT
5 Gnd
14 Lead 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 Gnd
8 Pwr Gnd
Rev. 11/19/98
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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