CS2844/CS3844
CS2845/CS3845
Current Mode PWM
Control Circuit
with 50% Max Duty Cycle
Description
Features
The CS3844/45 provides all the neces-
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.
Optimized for Offline
ꢀ
ꢀ
ꢀ
sary features to implement off-line
fixed frequency current-mode control
with a minimum number of external
components.
Control
Temp. Compensated
Oscillator
50% Max Duty-cycle Clamp
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 VREF is stabilized
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.
ꢀ V
Stabilized before
REF
Output Stage is Enabled
ꢀ Low Start-up Current
ꢀ Pulse-by-pulse Current
Limiting
ꢀ Improved Undervoltage
Lockout
Absolute Maximum Ratings
ꢀ Double Pulse Suppression
ꢀ 1% Trimmed Bandgap Ref.
Supply Voltage (ICC<30mA).........................................................................Self Limiting
Supply Voltage (Low Impedance Source) .................................................................30V
Output Current..............................................................................................................±1A
Output Energy (Capacitive Load)................................................................................5µJ
Analog Inputs (VFB, VSENSE) .........................................................................-0.3V to 5.5V
Error Amp Output Sink Current.............................................................................10mA
Lead Temperature Soldering
ꢀ High Current Totem Pole
Output
Package Options
8 Lead PDIP & SO Narrow
1
2
3
4
8
7
6
5
COMP
VFB
VREF
VCC
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
Sense
OSC
VOUT
Gnd
Block Diagram
14 Lead SO Narrow
1
2
3
4
5
6
7
14
13
12
COMP
VREF
VCC Undervoltage Lock-out
VCC
VCC Pwr
NC
NC
VFB
VCC
34V
Set/
5.0 Volt
VREF
11 VCC Pwr
NC
Reset Reference
Gnd
VFB
10
Sense
NC
VOUT
16V/10V
(8.4V/7.6V)
Internal
Bias
9
Gnd
8
OSC
Pwr Gnd
Error
Amplifier
VREF
R
R
Undervoltage
Lockout
-
16 Lead SO Wide
COMP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
NC
NC
+
2.50V
NC
VREF
VCC
VCCPwr
VO
Toggle
Flip-Flop
NOR
VOUT
OSC
Oscillator
COMP
VFB
S
R
SENSE
OSC
NC
2 R
Pwr Gnd
Gnd
R
1V
Pwr Gnd
NC
PWM
Latch
Current
Sensing
Comparator
NC
(
) indicates CS-2845/3845
Sense
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
Rev. 3/17/99
A
®
Company
1
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
