Semiconductor Components Industries, LLC, 2001
June, 2001 Rev. 3
1
Publication Order Number:
CS2842A/D
CS2842A, CS3842A,
CS2843A, CS3843A
Off-Line Current Mode
PWM Control Circuit with
Undervoltage Lockout
The CS284XA, CS384XA 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 X A 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 with an internally trimmed
discharge current to minimize variations in frequency. A precision
dutycycle clamp eliminates the need for an external oscillator when a
50% dutycycle is used. Dutycycles greater than 50% are also
possible. On board logic ensures that V
REF
is stabilized before the
output stage is enabled. Ion implant resistors provide tighter control of
undervoltage lockout.
Other features include low startup current, pulsebypulse current
limiting, and a highcurrent totem pole output for driving capacitive
loads, such as the gate of power MOSFET. The output is LOW in the
off state, consistent with Nchannel devices.
The CS384XA series of currentmode control ICs are available in
8 and14 lead packages for surface mount (SO) applications as well as
8 lead PDIP packages.
Features
Optimized for Offline Control
Internally Trimmed Temperature Compensated Oscillator
Maximum 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
= 2 or 3
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
x84yA
AWL
YYWW
MARKING
DIAGRAM
1
x84yA
ALYWX
8
1
CSx84yA
AWLYWW
14
See detailed ordering and shipping information in the package
dimensions section on page 8 of this data sheet.
ORDERING INFORMATION
CS2842A, CS3842A, CS2843A, CS3843A
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2
PIN CONNECTIONS
GND
OSC
V
OUT
Sense
V
CC
V
FB
V
REF
COMP
1
GND
OSC
Pwr GND
NC
V
OUT
Sense
V
CC
Pwr
NC
1
14
V
CC
V
FB
NC
NC
V
REF
COMP
8
DIP8 & SO8
SO14
Figure 1. Block Diagram
Set/
Reset
5.0 V
Reference
Undervoltage
Lockout Circuit
16 V/10 V
(8.4 V/7.6 V)
34 V
V
CC
GND
Output
Enable
Internal
Bias
Oscillator
OSC
2.50 V
V
CC
Pwr
V
REF
V
OUT
+
V
FB
COMP
Error
Amplifier
S
R
V
C
2R
R
1.0 V
Sense
Current
Sensing
Comparator
PWM
Latch
Pwr GND
( ) Indicates CS2843A/3843A
NOR
CS2842A, CS3842A, CS2843A, CS3843A
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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
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
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 CS2842A/CS2843A, 0
T
A
70
for CS3842A/CS3843A.
V
CC
= 15 V*; R
T
= 680
, C
T
= 0.022
F for triangular mode, R
T
= 10 k
, C
T
= 3.3 nF for sawtooth mode (see Figure 7);
unless otherwise stated.)
CS2842A/CS2843A
CS3842A/CS3843A
Characteristic
Test Conditions
Min
Typ
Max
Min
Typ
Max
Unit
Reference Section
Output Voltage
T
J
= 25
C, I
OUT
= 1.0 mA
4.95
5.00
5.05
4.90
5.00
5.10
V
Line Regulation
12
V
IN
25 V
6.0
20
6.0
20
mV
Load Regulation
1.0
I
OUT
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
V
Long Term Stability
T
A
= 125
C, 1.0 kHrs. (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 (see Figure 7), T
J
= 25
C
Triangular Mode (see Figure 7), T
J
= 25
C
47
47
52
52
57
57
47
44
52
52
57
60
kHz
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.)
Triangular Mode T
MIN
T
A
T
MAX
(Note 3.)
5.0
8.0
5.0
8.0
%
%
Amplitude
OSC peak to peak
1.7
1.7
V
Discharge Current
T
J
= 25
C
T
MIN
T
A
T
MAX
7.5
7.2
8.3
9.3
9.5
7.5
7.2
8.3
9.3
9.5
mA
mA
3. These parameters, although guaranteed, are not 100% tested in production.
*Adjust V
CC
above the start threshold before setting at 15 V.
CS2842A, CS3842A, CS2843A, CS3843A
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4
ELECTRICAL CHARACTERISTICS (continued)
(25
T
A
85
for CS2842A/CS2843A, 0
T
A
70
for CS3842A/CS3843A.
V
CC
= 15 V*; R
T
= 680
, C
T
= 0.022
F for triangular mode, R
T
= 10 k
, C
T
= 3.3 nF for sawtooth mode (see Figure 7);
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
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, 15 k
to ground
5.0
6.0
5.0
6.0
V
V
OUT
Low
V
FB
= 2.7 V, 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
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
Output Leakage
UVLO Active, V
OUT
= 0
0.01
10.00
0.01
10.00
A
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
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.
CS2842A, CS3842A, CS2843A, CS3843A
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5
ELECTRICAL CHARACTERISTICS (continued)
(25
T
A
85
for CS2842A/CS2843A, 0
T
A
70
for CS3842A/CS3843A.
V
CC
= 15 V*; R
T
= 680
, C
T
= 0.022
F for triangular mode, R
T
= 10 k
, C
T
= 3.3 nF for sawtooth mode (see Figure 7);
unless otherwise stated.)
CS2842A
CS3842A
CS2843A/CS3843A
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
Description
1
1
1
COMP
Error amp output, used to compensate error amplifier.
2
2
3
V
FB
Error amp inverting input.
3
3
5
Sense
Noninverting input to Current Sense Comparator.
4
4
7
OSC
Oscillator timing network with capacitor to ground, resistor to V
REF.
5
5
8
GND
Ground.
9
Pwr GND
Output driver ground.
6
6
10
V
OUT
Output drive pin.
11
V
CC
Pwr
Output driver positive supply.
7
7
12
V
CC
Positive power supply.
8
8
14
V
REF
Output of 5.0 V internal reference.
2, 4, 6, 13
NC
No connection.
TYPICAL PERFORMANCE CHARACTERISTICS
Figure 2. Oscillator Frequency vs. C
T
Figure 3. Oscillator Duty Cycle vs. R
T
900
800
700
600
500
Frequency
(kHz)
.0005
.001
.002
.04 .05
C
T
(
F)
400
300
200
100
.03
.02
.01
.003 .005
R
T
= 680
R
T
= 1.5 k
R
T
= 10 k
100
90
80
70
50
Duty Cycle (%)
R
T
(
)
40
30
20
10
60
100
200
300
400
500
700
1 k
2 k
3 k
4 k
5 k
7 k
10 k
CS2842A, CS3842A, CS2843A, CS3843A
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6
Figure 4. Test Circuit
V
REF
V
CC
V
OUT
GND
COMP
V
FB
Sense
OSC
0.1
F
0.1
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
CIRCUIT DESCRIPTION
CSX843A
8.4 V
7.6 V
CSX842A
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 5. Typical Undervoltage Characteristics
Undervoltage Lockout
During Undervoltage Lockout (Figure 5), the output
driver is biased to a high impedance state. The output should
be shunted to ground with a resistor to prevent output
leakage current from activating the power switch.
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 6). 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 6. Timing Diagram for Key CS2841B
Parameters
Switch
Current
EA Output
V
CC
I
O
V
O
OSC
RESET
OSC
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 oscillator components.
Setting the Oscillator
Oscillator timing capacitor, C
T
, is charged by V
REF
through R
T
and discharged by an internal current source.
During the discharge time, the internal clock signal blanks
out the output to the Low state, thus providing a user selected
maximum duty cycle clamp. Charge and discharge times are
determined by the formula:
CS2842A, CS3842A, CS2843A, CS3843A
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7
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
t
c
0.5534R
T
C
T
td
+
RTCT ln
2.3
*
0.0083RT
4.0
*
0.0083RT
The frequency and maximum duty cycle can be
determined using the Typical Performance Characteristic
graphs.
Grounding
High peak currents associated with capacitive loads
necessitate careful grounding techniques. Timing and
bypass capacitors should be connected close to GND pin in
a single point ground.
The transistor and 5.0 k
potentiometer, shown in the test
circuit, are used to sample the oscillator waveform and apply
and adjustable ramp to Sense.
Figure 7. Oscillator Timing Network and
Parameters
Internal Clock
Triangular Mode
V
OSC
V
OSC
Internal Clock
Small R
T
(
700 k
)
Large R
T
(
10 k
)
Sawtooth Mode
Timing Parameters
V
upper
V
lower
t
c
t
d
V
REF
OSC
GND
R
T
C
T
CS2842A, CS3842A, CS2843A, CS3843A
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8
ORDERING INFORMATION
Device
Temperature Range
Package
Shipping
CS2842ALN8
DIP8
50 Units/Rail
CS2843ALN8
25
C to 85
C
DIP8
50 Units/Rail
CS2842ALD14
25
C to 85
C
SO14
55 Units/Rail
CS2842ALDR14
SO14
2500 Tape & Reel
CS3842AGN8
DIP8
50 Units/Rail
CS3842AGD8
SO8
98 Units/Rail
CS3842AGDR8
SO8
2500 Tape & Reel
CS3842AGD14
SO14
55 Units/Rail
CS3842AGDR14
0
C to 70
C
SO14
2500 Tape & Reel
CS3843AGN8
0
C to 70
C
DIP8
50 Units/Rail
CS3843AGD8
SO8
98 Units/Rail
CS3843AGDR8
SO8
2500 Tape & Reel
CS3843AGD14
SO14
55 Units/Rail
CS3843AGDR14
SO14
2500 Tape & Reel
CS2842A, CS3842A, CS2843A, CS3843A
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9
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
_
_
_
_
CS2842A, CS3842A, CS2843A, CS3843A
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10
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
_
_
_
_
CS2842A, CS3842A, CS2843A, CS3843A
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11
Notes
CS2842A, CS3842A, CS2843A, CS3843A
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12
ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes
without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular
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
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PUBLICATION ORDERING INFORMATION
JAPAN: ON Semiconductor, Japan Customer Focus Center
4321 NishiGotanda, Shinagawaku, Tokyo, Japan 1410031
Phone: 81357402700
Email: r14525@onsemi.com
ON Semiconductor Website: http://onsemi.com
For additional information, please contact your local
Sales Representative.
CS2842A/D
Literature Fulfillment:
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P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 3036752175 or 8003443860 Toll Free USA/Canada
Fax: 3036752176 or 8003443867 Toll Free USA/Canada
Email: ONlit@hibbertco.com
N. American Technical Support: 8002829855 Toll Free USA/Canada
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