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Cherry Semiconductor Corporation

CS3844 Datasheet Preview

CS3844 Datasheet

Current Mode PWM Control Circuit

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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 VREF 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 (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
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
VCC
Gnd
VFB
COMP
OSC
Sense
VCC Undervoltage Lock-out
34V
16V/10V
(8.4V/7.6V)
Error
Amplifier
-
+
2.50V
Oscillator
Set/ 5.0 Volt
Reset Reference
R
VREF
Undervoltage
Lockout
R
Toggle
Flip-Flop
NOR
Internal
Bias
2R
R
S
R
1V
Current PWM
Sensing Latch
Comparator
( ) indicates CS-2845/3845
VCC Pwr
VREF
V O UT
Pwr Gnd
s Optimized for Offline
Control
s Temp. Compensated
Oscillator
s 50% Max Duty-cycle Clamp
s VREF 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
VFB 2
Sense 3
OSC 4
8 VREF
7 VCC
6 VOUT
5 Gnd
14 Lead SO Narrow
COMP 1
NC 2
14 VREF
13 NC
VFB 3
NC 4
Sense 5
NC 6
12 VCC
11 VCC Pwr
10 VOUT
9 Gnd
OSC 7
8 Pwr Gnd
16 Lead SO Wide
NC 1
16 NC
NC 2
COMP 3
VFB 4
SENSE 5
OSC 6
NC 7
15 VREF
14 VCC
13 VCCPwr
12 VO
11 Gnd
10 Pwr Gnd
NC 8
9 NC
Rev. 3/17/99
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
1 A ® Company




Cherry Semiconductor Corporation

CS3844 Datasheet Preview

CS3844 Datasheet

Current Mode PWM Control Circuit

No Preview Available !

Electrical Characteristics: -25 TA 85˚C for CS2844/2845, 0 TA 70˚C for CS3844/3845. VCC = 15V (Note 1); RT = 10k,
CT = 3.3nF for sawtooth mode., unless otherwise stated.
PARAMETER
s Reference Section
Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Output Variation
Output Noise Voltage
Long Term Stability
Output Short Circuit
TEST CONDITIONS
CS2844/CS2845
CS3844/CS3845
MIN TYP MAX MIN TYP MAX UNITS
TJ=25˚C, IREF=1mA
12VCC25V
1IREF20mA
(Note 2)
Line, Load, Temp. (Note 2)
10Hzf10kHz, TJ=25˚C (Note 2)
TA=125˚C, 1000 Hrs. (Note 2)
TA=25˚C
4.95 5.00 5.05 4.90 5.00 5.10 V
6 20
6 20 mV
6 25
6 25 mV
0.2 0.4
0.2 0.4 mV/˚C
4.90 5.10 4.82 5.18 V
50 50 µV
5 25
5 25 mV
-30 -100 -180 -30 -100 -180 mA
s Oscillator Section
Initial Accuracy
Voltage Stability
Temperature Stability
Amplitude
Sawtooth Mode, TJ=25˚C
12VCC25V
Sawtooth Mode TMINTATMAX
(Note 2)
VOSC (peak to peak)
47 52 57 47 52 57 kHz
0.2 1.0
0.2 1.0 %
5 5%
1.7 1.7 V
s Error Amp Section
Input Voltage
Input Bias Current
AVOL
Unity Gain Bandwidth
PSRR
Output Sink Current
Output Source Current
VOUT HIGH
VOUT LOW
VCOMP=2.5V
VFB=0V
2VOUT4V
(Note 2)
12VCC25V
VFB=2.7V, VCOMP=1.1V
VFB=2.3V, VCOMP=5V
VFB=2.3V, RL=15kto Gnd
VFB=2.7V, RL=15kto VREF
2.45 2.50 2.55 2.42 2.50 2.58 V
-0.3 -1.0
-0.3 -2.0 µA
65 90
65 90
dB
0.7 1.0
0.7 1.0
MHz
60 70
60 70
dB
26
26
mA
-0.5 -0.8
-0.5 -0.8
mA
56
56
V
0.7 1.1
0.7 1.1 V
s Current Sense Section
Gain
Maximum Input Signal
PSRR
Input Bias Current
Delay to Output
(Notes 3 & 4)
VCOMP=5V (Note 3)
12VCC25V (Note 3)
VSense=0V
TJ=25˚C (Note 2)
2.85 3.00 3.15 2.85 3.00 3.15 V/V
0.9 1.0 1.1 0.9 1.0 1.1 V
70 70 dB
-2 -10
-2 -10 µA
150 300
150 300 ns
s Output Section
Output Low Level
Output High Level
Rise Time
Fall Time
ISINK=20mA
ISINK=200mA
ISOURCE=20mA
ISOURCE=200mA
TJ=25˚C, CL=1nF (Note 2)
TJ=25˚C, CL=1nF (Note 2)
0.1 0.4
1.5 2.2
13.0 13.5
12.0 13.5
50 150
50 150
0.1 0.4 V
1.5 2.2 V
13.0 13.5
12.0 13.5
V
V
50 150 ns
50 150 ns
2


Part Number CS3844
Description Current Mode PWM Control Circuit
Maker Cherry Semiconductor Corporation
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CS3844 Datasheet PDF






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