©
Semiconductor Components Industries, LLC, 2001
June, 2001 Rev. 3
1
Publication Order Number:
CS2844/D
CS2844, CS3844, CS2845,
CS3845
Current Mode PWM
Control Circuit with
50% Max Duty Cycle
The CS3844/45 provides all the necessary features to implement
offline fixed frequency currentmode control with a minimum
number of external components.
T h e C S 3 8 4 4 f a m i l y i n c o r p o r a t e s a n e w p r e c i s i o n
temperaturecontrolled oscillator to minimize variations in frequency.
An internal toggle flipflop, which blanks the output every other clock
cycle, limits the dutycycle 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 16 V and turn off at
10 V. In the CS2845/CS3845 turn on is at 8.4 V and turn off at 7.6 V.
Other features include low startup current, pulsebypulse current
limiting, and a highcurrent totem pole output for driving capacitive
loads, such as gate of a power MOSFET. The output is low in the off
state, consistent with Nchannel devices.
Features
·
Optimized for OffLine Control
·
Temp. Compensated Oscillator
·
50% Max DutyCycle Clamp
·
V
REF
Stabilized Before Output Stage Is Enabled
·
Low StartUp Current
·
PulseByPulse Current Limiting
·
Improved Undervoltage Lockout
·
Double Pulse Suppression
·
1.0% Trimmed Bandgap Reference
·
High Current Totem Pole Output
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x
= 2 or 3
y
= 4 or 5
A
= Assembly Location
WL, L
= Wafer Lot
YY, Y
= Year
WW, W = Work Week
DIP8
N SUFFIX
CASE 626
1
8
SO8
D SUFFIX
CASE 751
1
8
SO14
D SUFFIX
CASE 751A
1
14
1
8
CSx84yN
AWL
YYWW
MARKING
DIAGRAMS
1
384yD
ALYW
8
1
CSx84yD14
AWLYWW
14
See detailed ordering and shipping information in the package
dimensions section on page 7 of this data sheet.
ORDERING INFORMATION
SO16L
DW SUFFIX
CASE 751G
1
16
1
CSx84yDW
AWLYYWW
16
CS2844, CS3844, CS2845, CS3845
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2
PIN CONNECTIONS
GND
OSC
V
OUT
Sense
V
CC
V
FB
V
REF
COMP
1
Pwr GND
OSC
GND
NC
V
OUT
Sense
V
CC
Pwr
NC
1
14
V
CC
V
FB
NC
NC
V
REF
COMP
8
NC
NC
1
16
Pwr GND
NC
GND
OSC
V
OUT
Sense
V
CC
Pwr
V
FB
V
CC
COMP
V
REF
NC
NC
NC
DIP8 & SO8
SO14
SO16L
Figure 1. Block Diagram
Set/
Reset
5.0 V
Reference
V
CC
Undervoltage Lockout
16 V/10 V
(8.4 V/7.6 V)
34 V
V
CC
GND
Internal
Bias
Oscillator
OSC
2.50 V
V
CC
Pwr
V
REF
V
OUT
+
V
FB
COMP
Error
Amplifier
S
R
2R
R
1.0 V
Sense
Current
Sensing
Comparator
PWM
Latch
Pwr GND
( ) Indicates CS2845/3845
NOR
V
REF
Undervoltage
Lockout
R
R
Toggle
FlipFlop
CS2844, CS3844, CS2845, CS3845
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3
MAXIMUM RATINGS*
Rating
Value
Unit
Supply Voltage (I
CC
< 30 mA)
Self Limiting
Supply Voltage (Low Impedance Source)
30
V
Output Current
±
1.0
A
Output Energy (Capacitive Load)
5.0
µ
J
Analog Inputs (V
FB
, Sense)
0.3 to + 5.5
V
Error Amp Output Sink Current
10
mA
Package Thermal Resistance, PDIP8
JunctiontoCase, R
JC
JunctiontoAmbient, R
JA
52
100
°
CW
°
CW
Package Thermal Resistance, SO8
JunctiontoCase, R
JC
JunctiontoAmbient, R
JA
45
165
°
CW
°
CW
Package Thermal Resistance, SO14
JunctiontoCase, R
JC
JunctiontoAmbient, R
JA
30
125
°
CW
°
CW
Package Thermal Resistance, SO16L
JunctiontoCase, R
JC
JunctiontoAmbient, R
JA
23
105
°
CW
°
CW
Lead Temperature Soldering:
Wave Solder (through hole styles only) (Note 1)
Reflow (SMD styles only) (Note 2)
260 peak
230 peak
°
C
°
C
1. 10 second maximum.
2. 60 second maximum above 183
°
C.
*The maximum package power dissipation must be observed.
ELECTRICAL CHARACTERISTICS
(25
°
T
A
85
°
for CS2844/2845, 0
°
T
A
70
°
for CS3844/CS3845.
V
CC
= 15 V*; R
T
= 10 k
, C
T
= 3.3 nF for sawtooth mode; unless otherwise stated.)
CS2844/CS2845
CS3844/CS3845
Characteristic
Test Conditions
Min
Typ
Max
Min
Typ
Max
Unit
Reference Section
Output Voltage
T
J
= 25
°
C, I
REF
= 1.0 mA
4.95
5.00
5.05
4.90
5.00
5.10
V
Line Regulation
12
V
CC
25 V
6.0
20
6.0
20
mV
Load Regulation
1.0
I
REF
20 mA
6.0
25
6.0
25
mV
Temperature Stability
Note 3.
0.2
0.4
0.2
0.4
mV/
°
C
Total Output Variation
Line, Load, Temperature. Note 3.
4.90
5.10
4.82
5.18
V
Output Noise Voltage
10 Hz
f
10 kHz, T
J
= 25
°
C. Note 3.
50
50
µ
V
Long Term Stability
T
A
= 125
°
C, 1000 Hrs. Note 3.
5.0
25
5.0
25
mV
Output Short Circuit
T
A
= 25
°
C
30
100
180
30
100
180
mA
Oscillator Section
Initial Accuracy
Sawtooth Mode, T
J
= 25
°
C
47
52
57
47
52
57
kHz
Voltage Stability
12
V
CC
25 V
0.2
1.0
0.2
1.0
%
Temperature Stability
Sawtooth Mode T
MIN
T
A
T
MAX
. Note 3.
5.0
5.0
%
Amplitude
V
OSC
(peak to peak)
1.7
1.7
V
3. These parameters, although guaranteed, are not 100% tested in production.
*Adjust V
CC
above the start threshold before setting at 15 V.
CS2844, CS3844, CS2845, CS3845
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4
ELECTRICAL CHARACTERISTICS (continued)
(25
°
T
A
85
°
for CS2844/2845, 0
°
T
A
70
°
for CS3844/CS3845.
V
CC
= 15 V*; R
T
= 10 k
, C
T
= 3.3 nF for sawtooth mode; unless otherwise stated.)
CS2842A/CS2843A
CS3842A/CS3843A
Characteristic
Test Conditions
Min
Typ
Max
Min
Typ
Max
Unit
Error Amp Section
Input Voltage
V
COMP
= 2.5 V
2.45
2.50
2.55
2.42
2.50
2.58
V
Input Bias Current
V
FB
= 0
0.3
1.0
0.3
2.0
µ
A
A
VOL
2.0
V
OUT
4.0 V
65
90
65
90
dB
Unity Gain Bandwidth
Note 4.
0.7
1.0
0.7
1.0
MHz
PSRR
12
V
CC
25 V
60
70
60
70
dB
Output Sink Current
V
FB
= 2.7 V, V
COMP
= 1.1 V
2.0
6.0
2.0
6.0
mA
Output Source Current
V
FB
= 2.3 V, V
COMP
= 5.0 V
0.5
0.8
0.5
0.8
mA
V
OUT
High
V
FB
= 2.3 V, R
L
= 15 k
to GND
5.0
6.0
5.0
6.0
V
V
OUT
Low
V
FB
= 2.7 V, R
L
= 15 k
to V
REF
0.7
1.1
0.7
1.1
V
Current Sense Section
Gain
Notes 5 & 6.
2.85
3.00
3.15
2.85
3.00
3.15
V/V
Maximum Input Signal
V
COMP
= 5.0 V. Note 5.
0.9
1.0
1.1
0.9
1.0
1.1
V
PSRR
12
V
CC
25 V. Note 5.
70
70
dB
Input Bias Current
V
SENSE
= 0
2.0
10
2.0
10
µ
A
Delay to Output
T
J
= 25
°
C. Note 4.
150
300
150
300
ns
Output Section
Output Low Level
I
SINK
= 20 mA
I
SINK
= 200 mA
0.1
1.5
0.4
2.2
0.1
1.5
0.4
2.2
V
V
Output High Level
I
SOURCE
= 20 mA
I
SOURCE
= 200 mA
13
12
13.5
13.5
13
12
13.5
13.5
V
V
Rise Time
T
J
= 25
°
C, C
L
= 1.0 nF. Note 4.
50
150
50
150
ns
Fall Time
T
J
= 25
°
C, C
L
= 1.0 nF. Note 4.
50
150
50
150
ns
Total Standby Current
Startup Current
0.5
1.0
0.5
1.0
mA
Operating Supply Current
V
FB
= V
SENSE
= 0 V,
R
T
= 10 k
, C
T
= 3.3 nF
11
17
11
17
mA
V
CC
Zener Voltage
I
CC
= 25 mA
34
34
V
PWM Section
Maximum Duty Cycle
46
48
50
46
48
50
%
Minimum Duty Cycle
0
0
%
4. These parameters, although guaranteed, are not 100% tested in production.
5. Parameters measured at trip point of latch with V
FB
= 0.
6. Gain defined as: A =
V
COMP
/
V
SENSE
; 0
V
SENSE
0.8 V.
*Adjust V
CC
above the start threshold before setting at 15 V.
CS2844, CS3844, CS2845, CS3845
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5
ELECTRICAL CHARACTERISTICS (continued)
(25
°
T
A
85
°
for CS2844/2845, 0
°
T
A
70
°
for CS3844/CS3845.
V
CC
= 15 V*; R
T
= 10 k
, C
T
= 3.3 nF for sawtooth mode; unless otherwise stated.)
CS2844
CS3844
CS2845/CS3845
Characteristic
Test Conditions
Min
Typ
Max
Min
Typ
Max
Min
Typ
Max
Unit
Undervoltage Lockout Section
Start Threshold
15
16
17
14.5
16
17.5
7.8
8.4
9.0
V
Min. Operating Voltage
After Turn On
9.0
10
11
8.5
10
11.5
7.0
7.6
8.2
V
*Adjust V
CC
above the start threshold before setting at 15 V.
PACKAGE PIN DESCRIPTION
Package Pin Number
DIP8 & SO8
SO14
Symbol
Symbol
Description
1
1
3
COMP
Error amp output, used to compensate error amplifier.
2
3
4
V
FB
Error amp inverting input.
3
5
5
Sense
Noninverting input to Current Sense Comparator.
4
7
6
OSC
Oscillator timing network with capacitor to ground, resistor to V
REF.
5
9
11
GND
Ground.
8
10
Pwr GND
Output driver ground.
6
10
12
V
OUT
Output drive pin.
11
13
V
CC
Pwr
Output driver positive supply.
7
12
14
V
CC
Positive power supply.
8
14
15
V
REF
Output of 5.0 V internal reference.
2, 4, 6, 13
1, 2, 7, 8,
9, 16
NC
No connection.
Figure 2. Test Circuit Open Loop Laboratory Test Fixture
V
REF
V
CC
V
OUT
GND
COMP
V
FB
Sense
OSC
0.1
µ
F
0.1
µ
F
R
T
1.0 k
1.0 W
2N2222
100 k
V
CC
V
REF
V
OUT
GND
A
5.0 k
Sense
ADJUST
C
T
4.7 k
4.7 k
1.0 k
ERROR AMP
ADJUST
CS2844, CS3844, CS2845, CS3845
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6
CIRCUIT DESCRIPTION
CSX845
8.4 V
7.6 V
CSX844
16 V
10 V
V
ON
V
OFF
ON/OFF Command
to reset of IC
V
CC
< 1.0 mA
< 15 mA
V
ON
V
OFF
V
CC
I
CC
Figure 3. Startup Voltage for CSX844 and CSX845
Undervoltage Lockout
During Undervoltage Lockout (Figure 3), the output
driver is biased to sink minor amounts of current. The output
should be shunted to ground with a resistor to prevent
activating the power switch with extraneous leakage
currents.
PWM Waveform
To generate the PWM waveform, the control voltage from
the error amplifier is compared to a current sense signal
which represents the peak output inductor current (Figure
4). An increase in V
CC
causes the inductor current slope to
increase, thus reducing the duty cycle. This is an inherent
feedforward characteristic of current mode control, since
the control voltage does not have to change during changes
of input supply voltage.
Figure 4. Timing Diagram
V
OSC
OSC
RESET
Toggle
F/F Output
EA Output
Switch
Current
V
CC
I
O
V
O
Figure 5. Duty Cycle Parameters
V
upper
V
lower
t
on
t
c
t
off
t
d
t
on
= t
c
t
off
= t
c
+ 2t
d
When the power supply sees a sudden large output current
increase, the control voltage will increase allowing the duty
cycle to momentarily increase. Since the duty cycle tends to
exceed the maximum allowed to prevent transformer
saturation in some power supplies, the internal oscillator
waveform provides the maximum duty cycle clamp as
programmed by the selection of OSC components.
Setting the Oscillator
The times t
c
and t
d
can be determined as follows:
tc
+
RTCT ln
VREF
*
Vlower
VREF
*
Vupper
td
+
RTCT ln
VREF
*
IdRT
*
Vlower
VREF
*
IdRT
*
Vupper
Substituting in typical values for the parameters in the
above formulas:
V
REF
= 5.0 V, V
upper
= 2.7 V, V
lower
= 1.0 V, I
d
= 8.3 mA
then:
tc
[
0.5534RTCT
td
+
RTCT ln
2.3
*
0.0083RT
4.0
*
0.0083RT
For better accuracy R
T
should be
10 k
.
Grounding
High peak currents associated with capacitive loads
necessitate careful grounding techniques. Timing and
bypass capacitors should be connected close to Gnd in a
single point ground.
The transistor and 5.0 k
potentiometer are used to
sample the oscillator waveform and apply an adjustable
ramp to Sense.
CS2844, CS3844, CS2845, CS3845
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7
ORDERING INFORMATION
Device
Temperature Range
Package
Shipping
CS2844LN8
DIP8
50 Units/Rail
CS2844LD14
SO14
55 Units/Rail
CS2844LDR14
SO14
2500 Tape & Reel
CS2844LDW16
25
°
C to 85
°
C
SO16L
48 Units/Rail
CS2844LDWR16
25
°
C to 85
°
C
SO16L
2500 Tape & Reel
CS2845LN8
DIP8
50 Units/Rail
CS2845LDW16
SO16L
48 Units/Rail
CS2845LDWR16
SO16L
2500 Tape & Reel
CS3844GN8
DIP8
50 Units/Rail
CS3844GD8
SO8
98 Units/Rail
CS3844GDR8
SO8
2500 Tape & Reel
CS3844GD14
SO14
55 Units/Rail
CS3844GDR14
SO14
2500 Tape & Reel
CS3844GDW16
SO16
48 Units/Rail
CS3844GDWR16
0
°
C to 70
°
C
SO16
2500 Tape & Reel
CS3845GN8
0
°
C to 70
°
C
DIP8
50 Units/Rail
CS3845GD8
SO8
98 Units/Rail
CS3845GDR8
SO8
2500 Tape & Reel
CS3845GD14
SO14
55 Units/Rail
CS3845GDR14
SO14
2500 Tape & Reel
CS3845GDW16
SO16L
48 Units/Rail
CS3845GDWR16
SO16L
2500 Tape & Reel
CS2844, CS3844, CS2845, CS3845
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8
PACKAGE DIMENSIONS
DIP8
N SUFFIX
CASE 62605
ISSUE L
NOTES:
1. DIMENSION L TO CENTER OF LEAD WHEN
FORMED PARALLEL.
2. PACKAGE CONTOUR OPTIONAL (ROUND OR
SQUARE CORNERS).
3. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
1
4
5
8
F
NOTE 2
A
B
T
SEATING
PLANE
H
J
G
D
K
N
C
L
M
M
A
M
0.13 (0.005)
B
M
T
DIM
MIN
MAX
MIN
MAX
INCHES
MILLIMETERS
A
9.40
10.16
0.370
0.400
B
6.10
6.60
0.240
0.260
C
3.94
4.45
0.155
0.175
D
0.38
0.51
0.015
0.020
F
1.02
1.78
0.040
0.070
G
2.54 BSC
0.100 BSC
H
0.76
1.27
0.030
0.050
J
0.20
0.30
0.008
0.012
K
2.92
3.43
0.115
0.135
L
7.62 BSC
0.300 BSC
M
---
10
---
10
N
0.76
1.01
0.030
0.040
_
_
SO8
D SUFFIX
CASE 75107
ISSUE W
SEATING
PLANE
1
4
5
8
N
J
X 45
_
K
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSION A AND B DO NOT INCLUDE MOLD
PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER
SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN
EXCESS OF THE D DIMENSION AT MAXIMUM
MATERIAL CONDITION.
A
B
S
D
H
C
0.10 (0.004)
DIM
A
MIN
MAX
MIN
MAX
INCHES
4.80
5.00
0.189
0.197
MILLIMETERS
B
3.80
4.00
0.150
0.157
C
1.35
1.75
0.053
0.069
D
0.33
0.51
0.013
0.020
G
1.27 BSC
0.050 BSC
H
0.10
0.25
0.004
0.010
J
0.19
0.25
0.007
0.010
K
0.40
1.27
0.016
0.050
M
0
8
0
8
N
0.25
0.50
0.010
0.020
S
5.80
6.20
0.228
0.244
X
Y
G
M
Y
M
0.25 (0.010)
Z
Y
M
0.25 (0.010)
Z
S
X
S
M
_
_
_
_
CS2844, CS3844, CS2845, CS3845
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9
PACKAGE DIMENSIONS
SO14
D SUFFIX
CASE 751A03
ISSUE F
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSIONS A AND B DO NOT INCLUDE
MOLD PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)
PER SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL
IN EXCESS OF THE D DIMENSION AT
MAXIMUM MATERIAL CONDITION.
A
B
G
P
7 PL
14
8
7
1
M
0.25 (0.010)
B
M
S
B
M
0.25 (0.010)
A
S
T
T
F
R
X 45
SEATING
PLANE
D
14 PL
K
C
J
M
_
DIM
MIN
MAX
MIN
MAX
INCHES
MILLIMETERS
A
8.55
8.75
0.337
0.344
B
3.80
4.00
0.150
0.157
C
1.35
1.75
0.054
0.068
D
0.35
0.49
0.014
0.019
F
0.40
1.25
0.016
0.049
G
1.27 BSC
0.050 BSC
J
0.19
0.25
0.008
0.009
K
0.10
0.25
0.004
0.009
M
0
7
0
7
P
5.80
6.20
0.228
0.244
R
0.25
0.50
0.010
0.019
_
_
_
_
SO16L
DW SUFFIX
CASE 751G03
ISSUE B
D
14X
B
16X
SEATING
PLANE
S
A
M
0.25
B
S
T
16
9
8
1
h
X 45
_
M
B
M
0.25
H
8X
E
B
A
e
T
A1
A
L
C
q
NOTES:
1. DIMENSIONS ARE IN MILLIMETERS.
2. INTERPRET DIMENSIONS AND TOLERANCES
PER ASME Y14.5M, 1994.
3. DIMENSIONS D AND E DO NOT INLCUDE MOLD
PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 PER SIDE.
5. DIMENSION B DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.13 TOTAL IN EXCESS
OF THE B DIMENSION AT MAXIMUM MATERIAL
CONDITION.
DIM
MIN
MAX
MILLIMETERS
A
2.35
2.65
A1
0.10
0.25
B
0.35
0.49
C
0.23
0.32
D
10.15
10.45
E
7.40
7.60
e
1.27 BSC
H
10.05
10.55
h
0.25
0.75
L
0.50
0.90
q
0
7
_
_
CS2844, CS3844, CS2845, CS3845
http://onsemi.com
10
Notes
CS2844, CS3844, CS2845, CS3845
http://onsemi.com
11
Notes
CS2844, CS3844, CS2845, CS3845
http://onsemi.com
12
ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes
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purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability,
including without limitation special, consequential or incidental damages. "Typical" parameters which may be provided in SCILLC data sheets and/or
specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be
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For additional information, please contact your local
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CS2844/D
Literature Fulfillment:
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