CS52845 Datasheet, PDF (1/8 Pages) Cherry Semiconductor Corporation – Current Mode PWM Control Circuit with 50% Max Duty Cycle

CS52845
Current Mode PWM Control Circuit
with 50% Max Duty Cycle
Description
The CS52845 provides all the nec-
essary features to implement off-
line fixed frequency current-mode
control with a minimum number
of external components.
The CS52845 incorporates a new
precision temperature-controlled
oscillator to minimize variations in
frequency. 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
CS52845 turn on is at 8.4V and
turn off at 7.6V.
Other features include low start-up
current, pulse-by-pulse current lim-
iting, and a high-current totem pole
output for driving capacitive loads,
such as gate of a power MOSFET.
The output 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
Reflow (SMD styles only) ...........60 sec. max above 183°C, 230°C peak
Block Diagram
V_CC
V_CC Undervoltage Lock-out
34V
Gnd
V_FB
COMP
OSC
Sense
8.4V/7.6V
Set/ 5.0 Volt
Reset Reference
Error
Amplifier
2.50V
Oscillator
V_REF
R Undervoltage
Lockout
R
Toggle
Flip-Flop
2R
R
S
R
1V
Current PWM
Sensing Latch
Comparator
NOR
Internal
Bias
V_CC Pwr
V_REF
V_OUT
Pwr Gnd
Features
s Optimized for Off-line
Control
s Temperature
Compensated Oscillator
s 50% Maximum 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
Reference
s High Current Totem Pole
Output
Package Options
8L SO Narrow
COMP 1
V_{FB 2}
Sense 3
OSC 4
8 VREF
7 VCC
6 VOUT
5 Gnd
14L SO Narrow
COMP 1
NC 2
14 V_REF
13 NC
V_FB 3
NC 4
Sense 5
NC 6
OSC 7
12 V_CC
11 V_CC Pwr
10 V_OUT
9 Gnd
8 Pwr Gnd
December, 2001 - Rev. 3
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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