ON CS3844GD8 Current mode pwm control circuit Datasheet

CS2844, CS3844, CS2845,
CS3845
Current Mode PWM
Control Circuit with
50% Max Duty Cycle
The CS3844/45 provides all the necessary 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 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 VREF 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 start–up current, pulse–by–pulse current
limiting, 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.
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MARKING
DIAGRAMS
8
CSx84yN
AWL
YYWW
DIP–8
N SUFFIX
CASE 626
8
1
8
1
8
1
SO–8
D SUFFIX
CASE 751
384yD
ALYW
1
14
Features
• Optimized for Off–Line Control
• Temp. Compensated Oscillator
• 50% Max Duty–Cycle Clamp
• VREF Stabilized Before Output Stage Is Enabled
• Low Start–Up Current
• Pulse–By–Pulse Current Limiting
• Improved Undervoltage Lockout
• Double Pulse Suppression
• 1.0% Trimmed Bandgap Reference
• High Current Totem Pole Output
SO–14
D SUFFIX
CASE 751A
14
1
CSx84yD14
AWLYWW
1
16
SO–16L
DW SUFFIX
CASE 751G
16
CSx84yDW
AWLYYWW
1
1
x
y
A
WL, L
YY, Y
WW, W
= 2 or 3
= 4 or 5
= Assembly Location
= Wafer Lot
= Year
= Work Week
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 7 of this data sheet.
 Semiconductor Components Industries, LLC, 2001
June, 2001 – Rev. 3
1
Publication Order Number:
CS2844/D
CS2844, CS3844, CS2845, CS3845
PIN CONNECTIONS
DIP–8 & SO–8
COMP
1
8
SO–14
1
COMP
NC
VFB
NC
Sense
NC
OSC
VREF
VCC
VFB
Sense
OSC
SO–16L
14
VOUT
GND
1
VREF
NC
VCC
VCC Pwr
VOUT
GND
Pwr GND
16
NC
VREF
VCC
VCC Pwr
VOUT
GND
Pwr GND
NC
NC
NC
COMP
VFB
Sense
OSC
NC
NC
VCC Undervoltage Lockout
VCC
VCC Pwr
34 V
Set/
Reset
GND
5.0 V
Reference
16 V/10 V
(8.4 V/7.6 V)
Error
Amplifier
COMP
Internal
Bias
–
VFB
VREF
R
VREF
Undervoltage
Lockout
+
2.50 V
R
Toggle
Flip–Flop
OSC
NOR
Oscillator
VOUT
S
2R
R
R
1.0 V
PWM
Latch
Current
Sensing
Comparator
Sense
( ) Indicates CS2845/3845
Figure 1. Block Diagram
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2
Pwr GND
CS2844, CS3844, CS2845, CS3845
MAXIMUM RATINGS*
Rating
Value
Unit
Self Limiting
–
30
V
Output Current
±1.0
A
Output Energy (Capacitive Load)
5.0
µJ
–0.3 to + 5.5
V
Error Amp Output Sink Current
10
mA
Package Thermal Resistance, PDIP–8
Junction–to–Case, RθJC
Junction–to–Ambient, RθJA
52
100
°CW
°CW
Package Thermal Resistance, SO–8
Junction–to–Case, RθJC
Junction–to–Ambient, RθJA
45
165
°CW
°CW
Package Thermal Resistance, SO–14
Junction–to–Case, RθJC
Junction–to–Ambient, RθJA
30
125
°CW
°CW
Package Thermal Resistance, SO–16L
Junction–to–Case, RθJC
Junction–to–Ambient, RθJA
23
105
°CW
°CW
260 peak
230 peak
°C
°C
Supply Voltage (ICC < 30 mA)
Supply Voltage (Low Impedance Source)
Analog Inputs (VFB, Sense)
Lead Temperature Soldering:
Wave Solder (through hole styles only) (Note 1)
Reflow (SMD styles only) (Note 2)
1. 10 second maximum.
2. 60 second maximum above 183°C.
*The maximum package power dissipation must be observed.
ELECTRICAL CHARACTERISTICS (–25° ≤ TA ≤ 85° for CS2844/2845, 0° ≤ TA ≤ 70° for CS3844/CS3845.
VCC = 15 V*; RT = 10 kΩ, CT = 3.3 nF for sawtooth mode; unless otherwise stated.)
CS2844/CS2845
Characteristic
Test Conditions
CS3844/CS3845
Min
Typ
Max
Min
Typ
Max
Unit
4.95
5.00
5.05
4.90
5.00
5.10
V
Reference Section
Output Voltage
TJ = 25°C, IREF = 1.0 mA
Line Regulation
12 ≤ VCC ≤ 25 V
–
6.0
20
–
6.0
20
mV
Load Regulation
1.0 ≤ IREF ≤ 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, TJ = 25°C. Note 3.
–
50
–
–
50
–
µV
Long Term Stability
TA = 125°C, 1000 Hrs. Note 3.
–
5.0
25
–
5.0
25
mV
Output Short Circuit
TA = 25°C
–30
–100
–180
–30
–100
–180
mA
Initial Accuracy
Sawtooth Mode, TJ = 25°C
47
52
57
47
52
57
kHz
Voltage Stability
12 ≤ VCC ≤ 25 V
–
0.2
1.0
–
0.2
1.0
%
Temperature Stability
Sawtooth Mode TMIN ≤ TA ≤ TMAX. Note 3.
–
5.0
–
–
5.0
–
%
Amplitude
VOSC (peak to peak)
–
1.7
–
–
1.7
–
V
Oscillator Section
3. These parameters, although guaranteed, are not 100% tested in production.
*Adjust VCC above the start threshold before setting at 15 V.
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3
CS2844, CS3844, CS2845, CS3845
ELECTRICAL CHARACTERISTICS (continued) (–25° ≤ TA ≤ 85° for CS2844/2845, 0° ≤ TA ≤ 70° for CS3844/CS3845.
VCC = 15 V*; RT = 10 kΩ, CT = 3.3 nF for sawtooth mode; unless otherwise stated.)
Characteristic
Test Conditions
CS2842A/CS2843A
CS3842A/CS3843A
Min
Typ
Max
Min
Typ
Max
Unit
2.45
2.50
2.55
2.42
2.50
2.58
V
Error Amp Section
Input Voltage
VCOMP = 2.5 V
Input Bias Current
VFB = 0
–
–0.3
–1.0
–
–0.3
–2.0
µA
AVOL
2.0 ≤ VOUT ≤ 4.0 V
65
90
–
65
90
–
dB
Unity Gain Bandwidth
Note 4.
0.7
1.0
–
0.7
1.0
–
MHz
PSRR
12 ≤ VCC ≤ 25 V
60
70
–
60
70
–
dB
Output Sink Current
VFB = 2.7 V, VCOMP = 1.1 V
2.0
6.0
–
2.0
6.0
–
mA
Output Source Current
VFB = 2.3 V, VCOMP = 5.0 V
–0.5
–0.8
–
–0.5
–0.8
–
mA
VOUT High
VFB = 2.3 V, RL = 15 kΩ to GND
5.0
6.0
–
5.0
6.0
–
V
VOUT Low
VFB = 2.7 V, RL = 15 kΩ to VREF
–
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
VCOMP = 5.0 V. Note 5.
0.9
1.0
1.1
0.9
1.0
1.1
V
PSRR
12 ≤ VCC ≤ 25 V. Note 5.
–
70
–
–
70
–
dB
Input Bias Current
VSENSE = 0
–
–2.0
–10
–
–2.0
–10
µA
Delay to Output
TJ = 25°C. Note 4.
–
150
300
–
150
300
ns
Output Low Level
ISINK = 20 mA
ISINK = 200 mA
–
–
0.1
1.5
0.4
2.2
–
–
0.1
1.5
0.4
2.2
V
V
Output High Level
ISOURCE = 20 mA
ISOURCE = 200 mA
13
12
13.5
13.5
–
–
13
12
13.5
13.5
–
–
V
V
Rise Time
TJ = 25°C, CL = 1.0 nF. Note 4.
–
50
150
–
50
150
ns
Fall Time
TJ = 25°C, CL = 1.0 nF. Note 4.
–
50
150
–
50
150
ns
–
0.5
1.0
–
0.5
1.0
mA
Output Section
Total Standby Current
–
Startup Current
Operating Supply Current
VFB = VSENSE = 0 V,
RT = 10 kΩ, CT = 3.3 nF
–
11
17
–
11
17
mA
VCC Zener Voltage
ICC = 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 VFB = 0.
6. Gain defined as: A = ∆VCOMP/∆VSENSE; 0 ≤ VSENSE ≤ 0.8 V.
*Adjust VCC above the start threshold before setting at 15 V.
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4
CS2844, CS3844, CS2845, CS3845
ELECTRICAL CHARACTERISTICS (continued) (–25° ≤ TA ≤ 85° for CS2844/2845, 0° ≤ TA ≤ 70° for CS3844/CS3845.
VCC = 15 V*; RT = 10 kΩ, CT = 3.3 nF for sawtooth mode; unless otherwise stated.)
CS2844
Characteristic
Test Conditions
CS3844
CS2845/CS3845
Min
Typ
Max
Min
Typ
Max
Min
Typ
Max
Unit
15
16
17
14.5
16
17.5
7.8
8.4
9.0
V
9.0
10
11
8.5
10
11.5
7.0
7.6
8.2
V
Undervoltage Lockout Section
Start Threshold
–
Min. Operating Voltage
After Turn On
*Adjust VCC above the start threshold before setting at 15 V.
PACKAGE PIN DESCRIPTION
Package Pin Number
DIP–8 & SO–8
SO–14
Symbol
Symbol
1
1
3
COMP
2
3
4
VFB
3
5
5
Sense
4
7
6
OSC
Oscillator timing network with capacitor to ground, resistor to VREF.
5
9
11
GND
Ground.
–
8
10
Pwr GND
6
10
12
VOUT
–
11
13
VCC Pwr
7
12
14
VCC
Positive power supply.
Output of 5.0 V internal reference.
8
14
15
VREF
–
2, 4, 6, 13
1, 2, 7, 8,
9, 16
NC
Description
Error amp output, used to compensate error amplifier.
Error amp inverting input.
Noninverting input to Current Sense Comparator.
Output driver ground.
Output drive pin.
Output driver positive supply.
No connection.
VREF
RT
A
VCC
2N2222
4.7 kΩ
COMP
VREF
100 kΩ
1.0 kΩ
ERROR AMP
ADJUST
4.7 kΩ
0.1 µF
VFB
5.0 kΩ
Sense
ADJUST
VCC
1.0 kΩ
1.0 W
0.1 µF
Sense
VOUT
OSC
GND
VOUT
GND
CT
Figure 2. Test Circuit Open Loop Laboratory Test Fixture
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5
CS2844, CS3844, CS2845, CS3845
CIRCUIT DESCRIPTION
Vupper
VCC
ON/OFF Command
to reset of IC
Vlower
VON
VOFF
CSX844
CSX845
16 V
8.4 V
10 V
ton
toff
td
tc
7.6 V
ton = tc
toff = tc + 2td
ICC
Figure 5. Duty Cycle Parameters
< 15 mA
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.
< 1.0 mA
VCC
VON VOFF
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.
Setting the Oscillator
The times tc and td can be determined as follows:
V
Vlower
tc RTCT ln REF
VREF Vupper
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 VCC causes the inductor current slope to
increase, thus reducing the duty cycle. This is an inherent
feed–forward characteristic of current mode control, since
the control voltage does not have to change during changes
of input supply voltage.
V
IdRT Vlower
td RTCT ln REF
VREF IdRT Vupper
Substituting in typical values for the parameters in the
above formulas:
VREF = 5.0 V, Vupper = 2.7 V, Vlower = 1.0 V, Id = 8.3 mA
then:
tc 0.5534RTCT
2.3 0.0083RT
td RTCT ln
4.0 0.0083RT
VOSC
For better accuracy RT should be ≥ 10 kΩ.
OSC
RESET
Grounding
Toggle
F/F Output
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 kΩ potentiometer are used to
sample the oscillator waveform and apply an adjustable
ramp to Sense.
EA Output
Switch
Current
VCC
IO
VO
Figure 4. Timing Diagram
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6
CS2844, CS3844, CS2845, CS3845
ORDERING INFORMATION
Device
Temperature Range
Package
Shipping
CS2844LN8
DIP–8
50 Units/Rail
CS2844LD14
SO–14
55 Units/Rail
CS2844LDR14
SO–14
2500 Tape & Reel
CS2844LDW16
SO–16L
48 Units/Rail
SO–16L
2500 Tape & Reel
DIP–8
50 Units/Rail
CS2845LDW16
SO–16L
48 Units/Rail
CS2845LDWR16
SO–16L
2500 Tape & Reel
CS3844GN8
DIP–8
50 Units/Rail
CS3844GD8
SO–8
98 Units/Rail
CS3844GDR8
SO–8
2500 Tape & Reel
CS3844GD14
SO–14
55 Units/Rail
CS3844GDR14
SO–14
2500 Tape & Reel
CS3844GDW16
SO–16
48 Units/Rail
SO–16
2500 Tape & Reel
CS2844LDWR16
–25°C
25°C to 85°C
CS2845LN8
CS3844GDWR16
CS3845GN8
0°C to 70°C
DIP–8
50 Units/Rail
CS3845GD8
SO–8
98 Units/Rail
CS3845GDR8
SO–8
2500 Tape & Reel
CS3845GD14
SO–14
55 Units/Rail
CS3845GDR14
SO–14
2500 Tape & Reel
CS3845GDW16
SO–16L
48 Units/Rail
CS3845GDWR16
SO–16L
2500 Tape & Reel
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7
CS2844, CS3844, CS2845, CS3845
PACKAGE DIMENSIONS
DIP–8
N SUFFIX
CASE 626–05
ISSUE L
8
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.
5
–B–
1
4
DIM
A
B
C
D
F
G
H
J
K
L
M
N
F
–A–
NOTE 2
L
C
J
–T–
MILLIMETERS
MIN
MAX
9.40
10.16
6.10
6.60
3.94
4.45
0.38
0.51
1.02
1.78
2.54 BSC
0.76
1.27
0.20
0.30
2.92
3.43
7.62 BSC
--10
0.76
1.01
INCHES
MIN
MAX
0.370
0.400
0.240
0.260
0.155
0.175
0.015
0.020
0.040
0.070
0.100 BSC
0.030
0.050
0.008
0.012
0.115
0.135
0.300 BSC
--10
0.030
0.040
N
SEATING
PLANE
D
M
K
G
H
0.13 (0.005)
M
T A
M
B
M
SO–8
D SUFFIX
CASE 751–07
ISSUE W
–X–
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
8
5
0.25 (0.010)
S
B
1
M
Y
M
4
K
–Y–
G
C
N
X 45 SEATING
PLANE
–Z–
0.10 (0.004)
H
D
0.25 (0.010)
M
Z Y
S
X
M
S
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8
J
DIM
A
B
C
D
G
H
J
K
M
N
S
MILLIMETERS
MIN
MAX
4.80
5.00
3.80
4.00
1.35
1.75
0.33
0.51
1.27 BSC
0.10
0.25
0.19
0.25
0.40
1.27
0
8
0.25
0.50
5.80
6.20
INCHES
MIN
MAX
0.189
0.197
0.150
0.157
0.053
0.069
0.013
0.020
0.050 BSC
0.004
0.010
0.007
0.010
0.016
0.050
0
8
0.010
0.020
0.228
0.244
CS2844, CS3844, CS2845, CS3845
PACKAGE DIMENSIONS
SO–14
D SUFFIX
CASE 751A–03
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–
14
8
–B–
1
P 7 PL
0.25 (0.010)
7
G
M
B
M
F
R X 45 C
–T–
SEATING
PLANE
M
T B
J
M
K
D 14 PL
0.25 (0.010)
S
A
S
DIM
A
B
C
D
F
G
J
K
M
P
R
MILLIMETERS
MIN
MAX
8.55
8.75
3.80
4.00
1.35
1.75
0.35
0.49
0.40
1.25
1.27 BSC
0.19
0.25
0.10
0.25
0
7
5.80
6.20
0.25
0.50
INCHES
MIN
MAX
0.337
0.344
0.150
0.157
0.054
0.068
0.014
0.019
0.016
0.049
0.050 BSC
0.008
0.009
0.004
0.009
0
7
0.228
0.244
0.010
0.019
SO–16L
DW SUFFIX
CASE 751G–03
ISSUE B
A
D
9
1
8
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.
16X
M
14X
e
T A
S
B
h X 45 S
L
A
0.25
B
B
A1
H
E
0.25
8X
M
B
M
16
SEATING
PLANE
T
C
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9
DIM
A
A1
B
C
D
E
e
H
h
L
MILLIMETERS
MIN
MAX
2.35
2.65
0.10
0.25
0.35
0.49
0.23
0.32
10.15
10.45
7.40
7.60
1.27 BSC
10.05
10.55
0.25
0.75
0.50
0.90
0
7
CS2844, CS3844, CS2845, CS3845
Notes
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10
CS2844, CS3844, CS2845, CS3845
Notes
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11
CS2844, CS3844, CS2845, CS3845
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
specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be
validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others.
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intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or
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SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable
attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim
alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer.
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For additional information, please contact your local
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http://onsemi.com
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