
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.
1
Features
V
CC
Gnd
COMP
OSC
Sense
V
REF
V
UnLockout
IBias
NOR
S
R
PWM
Current
Comparator
R
2 R
1V
AmError
-
+
2.50V
Set/
Reset
V
CC
Undervoltage Lock-out
34V
8.4V/7.6V
R
R
V
FB
V
CC
Pwr
V
OUT
Pwr Gnd
Oscillator
Toggle
5.0 Volt
Reference
I
Optimized for Off-line
Control
Temperature
Compensated Oscillator
50% Maximum Duty-cycle
Clamp
V
REF
Stabilized before
Output Stage is Enabled
Low Start-up Current
Pulse-by-pulse Current
Limiting
Improved Undervoltage
Lockout
Double Pulse Suppression
1% Trimmed Bandgap
Reference
High Current Totem Pole
Output
I
I
I
I
I
I
I
I
I
Package Options
C
Current Mode PWM Control Circuit
with 50% Max Duty Cycle
Description
CS52845
Block Diagram
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
10
7
14
13
12
8
1
2
3
4
5
6
11
9
COMP
NC
V
FB
NC
Sense
NC
OSC
V
REF
NC
V
CC
V
CC
Pwr
V
OUT
Pwr Gnd
Gnd
14L SO Narrow
1
7
8
2
3
4
5
6
COMP
V
FB
Sense
OSC
V
REF
V
CC
V
OUT
Gnd
8L SO Narrow
Rev. 3/4/99
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
A
Company