Semiconductor Components Industries, LLC, 2001
June, 2001 – Rev. 3 1Publication 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
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.
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
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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
DIP–8
N SUFFIX
CASE 626
1
8
SO–8
D SUFFIX
CASE 751
1
8
SO–14
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
SO–16L
DW SUFFIX
CASE 751G
1
16
1
CSx84yDW
AWLYYWW
16
CS2844, CS3844, CS2845, CS3845
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2
PIN CONNECTIONS
GNDOSC VOUT
Sense VCC
VFB
VREF
COMP1
Pwr GNDOSC GNDNC VOUT
Sense VCC PwrNC
114
VCC
VFB
NCNC VREF
COMP
8
NCNC
116
Pwr GNDNC GNDOSC VOUT
Sense VCC PwrVFB
VCC
COMP VREF
NC NCNC
DIP–8 & SO–8 SO–14 SO–16L
Figure 1. Block Diagram
Set/
Reset 5.0 V
Reference
VCC Undervoltage Lockout
16 V/10 V
(8.4 V/7.6 V)
34 V
VCC
GND
Internal
Bias
Oscillator
OSC
2.50 V
VCC Pwr
VREF
VOUT
+
–
VFB
COMP
Error
Amplifier
S
R
2R
R1.0 V
Sense
Current
Sensing
Comparator
PWM
Latch
Pwr GND
( ) Indicates CS2845/3845
NOR
VREF
Undervoltage
Lockout
R
RToggle
Flip–Flop
CS2844, CS3844, CS2845, CS3845
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3
MAXIMUM RATINGS*
Rating Value Unit
Supply Voltage (ICC < 30 mA) Self Limiting –
Supply Voltage (Low Impedance Source) 30 V
Output Current ±1.0 A
Output Energy (Capacitive Load) 5.0 µJ
Analog Inputs (VFB, Sense) –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
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° ≤ 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 CS3844/CS3845
Characteristic Test Conditions Min Typ Max Min Typ Max Unit
Reference Section
Output Voltage TJ = 25°C, IREF = 1.0 mA 4.95 5.00 5.05 4.90 5.00 5.10 V
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
Oscillator Section
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
3. These parameters, although guaranteed, are not 100% tested in production.
*Adjust VCC above the start threshold before setting at 15 V.
CS2844, CS3844, CS2845, CS3845
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4
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.)
CS2842A/CS2843A CS3842A/CS3843A
Characteristic Test Conditions Min Typ Max Min Typ Max Unit
Error Amp Section
Input Voltage VCOMP = 2.5 V 2.45 2.50 2.55 2.42 2.50 2.58 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 Section
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
Total Standby Current
Startup Current – – 0.5 1.0 – 0.5 1.0 mA
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. Gai n defined as: A = ∆VCOMP/∆VSENSE; 0 ≤ VSENSE ≤ 0.8 V.
*Adjust VCC above the start threshold before setting at 15 V.
CS2844, CS3844, CS2845, CS3845
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5
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 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 VCC above the start threshold before setting at 15 V.
PACKAGE PIN DESCRIPTION
Package Pin Number
DIP–8 & SO–8 SO–14 Symbol Symbol Description
1 1 3 COMP Error amp output, used to compensate error amplifier.
2 3 4 VFB 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 VREF.
5 9 11 GND Ground.
– 8 10 Pwr GND Output driver ground.
6 10 12 VOUT Output drive pin.
–11 13 VCC Pwr Output driver positive supply.
7 12 14 VCC Positive power supply.
8 14 15 VREF 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
VREF
VCC
VOUT
GND
COMP
VFB
Sense
OSC
0.1 µF
0.1 µF
RT
1.0 kΩ
1.0 W
2N2222
100 kΩ
VCC
VREF
VOUT
GND
A
5.0 kΩ
Sense
ADJUST
CT
4.7 kΩ
4.7 kΩ
1.0 kΩ
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
VON
VOFF
ON/OFF Command
to reset of IC
VCC
< 1.0 mA
< 15 mA
VON VOFF
VCC
ICC
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 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.
Figure 4. Timing Diagram
VOSC
OSC
RESET
Toggle
F/F Output
EA Output
Switch
Current
VCC
IO
VO
Figure 5. Duty Cycle Parameters
Vupper
Vlower
ton
tc
toff
td
ton = tc
toff = tc + 2td
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 tc and td can be determined as follows:
tcRTCTlnVREF Vlower
VREF Vupper
tdRTCTlnVREF IdRTVlower
VREF IdRTVupper
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:
tc0.5534RTCT
tdRTCTln2.3 0.0083RT
4.0 0.0083RT
For better accuracy RT should be ≥ 10 kΩ.
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 kΩ 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 DIP–8 50 Units/Rail
CS2844LD14 SO–14 55 Units/Rail
CS2844LDR14 SO–14 2500 Tape & Reel
CS2844LDW16
25°Cto85°C
SO–16L 48 Units/Rail
CS2844LDWR16 –25°C to 85°CSO–16L 2500 Tape & Reel
CS2845LN8 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
CS3844GDWR16
0°Cto70°C
SO–16 2500 Tape & Reel
CS3845GN8 0°C to 70°CDIP–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
CS2844, CS3844, CS2845, CS3845
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8
PACKAGE DIMENSIONS
DIP–8
N SUFFIX
CASE 626–05
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.
14
58
F
NOTE 2 –A–
–B–
–T–
SEATING
PLANE
H
J
GDK
N
C
L
M
M
A
M
0.13 (0.005) B M
T
DIM MIN MAX MIN MAX
INCHESMILLIMETERS
A9.40 10.16 0.370 0.400
B6.10 6.60 0.240 0.260
C3.94 4.45 0.155 0.175
D0.38 0.51 0.015 0.020
F1.02 1.78 0.040 0.070
G2.54 BSC 0.100 BSC
H0.76 1.27 0.030 0.050
J0.20 0.30 0.008 0.012
K2.92 3.43 0.115 0.135
L7.62 BSC 0.300 BSC
M--- 10 --- 10
N0.76 1.01 0.030 0.040
SO–8
D SUFFIX
CASE 751–07
ISSUE W
SEATING
PLANE
1
4
58
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
BS
D
H
C
0.10 (0.004)
DIM
A
MIN MAX MIN MAX
INCHES
4.80 5.00 0.189 0.197
MILLIMETERS
B3.80 4.00 0.150 0.157
C1.35 1.75 0.053 0.069
D0.33 0.51 0.013 0.020
G1.27 BSC 0.050 BSC
H0.10 0.25 0.004 0.010
J0.19 0.25 0.007 0.010
K0.40 1.27 0.016 0.050
M0 8 0 8
N0.25 0.50 0.010 0.020
S5.80 6.20 0.228 0.244
–X–
–Y–
G
M
Y
M
0.25 (0.010)
–Z–
Y
M
0.25 (0.010) Z SXS
M
CS2844, CS3844, CS2845, CS3845
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9
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–
–B–
G
P7 PL
14 8
71 M
0.25 (0.010) B M
S
B
M
0.25 (0.010) A S
T
–T–
F
RX 45
SEATING
PLANE D14 PL K
C
J
M
DIM MIN MAX MIN MAX
INCHESMILLIMETERS
A8.55 8.75 0.337 0.344
B3.80 4.00 0.150 0.157
C1.35 1.75 0.054 0.068
D0.35 0.49 0.014 0.019
F0.40 1.25 0.016 0.049
G1.27 BSC 0.050 BSC
J0.19 0.25 0.008 0.009
K0.10 0.25 0.004 0.009
M0 7 0 7
P5.80 6.20 0.228 0.244
R0.25 0.50 0.010 0.019
SO–16L
DW SUFFIX
CASE 751G–03
ISSUE B
D
14X
B16X
SEATING
PLANE
S
A
M
0.25 B S
T
16 9
81
hX 45
M
B
M
0.25
H8X
E
B
A
eT
A1
A
L
C
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
A2.35 2.65
A1 0.10 0.25
B0.35 0.49
C0.23 0.32
D10.15 10.45
E7.40 7.60
e1.27 BSC
H10.05 10.55
h0.25 0.75
L0.50 0.90
0 7
CS2844, CS3844, CS2845, CS3845
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10
Notes
CS2844, CS3844, CS2845, CS3845
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11
Notes
CS2844, CS3844, CS2845, CS3845
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12
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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.
SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
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death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold
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alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer.
PUBLICATION ORDERING INFORMATION
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4–32–1 Nishi–Gotanda, Shinagawa–ku, Tokyo, Japan 141–0031
Phone: 81–3–5740–2700
Email: r14525@onsemi.com
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For additional information, please contact your local
Sales Representative.
CS2844/D
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