CS2844 Datasheet, PDF (1/6 Pages) Cherry Semiconductor Corporation – Current Mode PWM Control Circuit with 50% Max Duty Cycle

CS2844/CS3844
CS2845/CS3845
Current Mode PWM Control Circuit
with 50% Max Duty Cycle
Description
Features
The CS3844/45 provides all the neces-
sary features to implement off-line
fixed frequency current-mode control
with a minimum number of external
components.
The CS3844 family incorporates a new
precision temperature-controlled oscil-
lator to minimize variations in fre-
quency. An internal toggle flip-flop,
which blanks the output every other
clock cycle, limits the duty-cycle range
to less than 50%. An undervoltage
lockout ensures that V_REF is stabilized
before the output stage is enabled. In
the CS2844/CS3844 turn on occurs at
16V and turn off at 10V. In the
CS2845/CS3845 turn on is at 8.4V and
turn off at 7.6V.
Other features include low start-up
current, pulse-by-pulse current limit-
ing, and a high-current totem pole out-
put for driving capacitive loads, such
as gate of a power MOSFET. The out-
put is low in the off state, consistent
with N-channel devices.
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
V_CC
Gnd
V_FB
COMP
OSC
Sense
V_CC Undervoltage Lock-out
34V
16V/10V
(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
Internal
Bias
2R
R
S
R
1V
Current PWM
Sensing Latch
Comparator
( ) indicates CS-2845/3845
V_CC Pwr
V_REF
V _{O UT}
Pwr Gnd
s Optimized for Offline
Control
s Temp. Compensated
Oscillator
s 50% Max Duty-cycle Clamp
s V_REF Stabilized before
Output Stage is Enabled
s Low Start-up Current
s Pulse-by-pulse Current
Limiting
s Improved Undervoltage
Lockout
s Double Pulse Suppression
s 1% Trimmed Bandgap Ref.
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
14 Lead SO Narrow
COMP 1
NC 2
14 V_REF
13 NC
V_FB 3
NC 4
Sense 5
NC 6
12 V_CC
11 V_CC Pwr
10 V_OUT
9 Gnd
OSC 7
8 Pwr Gnd
16 Lead SO Wide
NC 1
16 NC
NC 2
COMP 3
V_FB 4
SENSE 5
OSC 6
15 V_REF
14 V_CC
13 V_CCPwr
12 V_O
11 Gnd
NC 7
10 Pwr Gnd
NC 8
9 NC
Rev. 3/17/99
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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