MICROSEMI SG1842J/883B

L I N D O C # : 1842
SG1842/SG1843 Series
CURRENT MODE PWM CONTROLLER
T
H E
I
N F I N I T E
P
O W E R
I
O F
P
N N O VA T I O N
R O D U C T I O N
DESCRIPTION
The SG1842/43 family of control IC's
provides all the necessary features to
implement off-line fixed frequency,
current-mode switching power supplies
with a minimum number of external
components. Current-mode
architecture demonstrates improved
line regulation, improved load
regulation, pulse-by-pulse current
limiting and inherent protection of the
power supply output switch.
The bandgap reference is trimmed to
±1% over temperature. Oscillator
discharge current is trimmed to less
than ±10%. The SG1842/43 has under-
OF
voltage lockout, current limiting
circuitry and start-up current of less
than 1mA.
The totem-pole output is optimized
to drive the gate of a power MOSFET.
The output is low in the off state to
provide direct interface to an N
channel device.
The SG1842/43 is specified for
operation over the full military ambient
temperature range of -55°C to 125°C.
The SG2842/43 is specified for the
industrial range of -25°C to 85°C, and
the SG3842/43 is designed for the
commercial range of 0°C to 70°C.
S G 3 8 4 2 I N A F LY B A C K C O N V E R T E R
■ AVAILABLE TO MIL-STD-883B AND DESC
SMD
■ SCHEDULED FOR MIL-M38510 QPL LISTING
■ RADIATION DATA AVAILABLE
■ LINFINITY LEVEL "S" PROCESSING AVAILABLE
IST
SG3842
TA (°C)
0 to 70
-25 to 85
-55 to 125
MIL-STD/883
DESC
M
N
Plastic DIP
14-pin
H E E T
HIGH RELIABILITY FEATURES
VCC
Plastic DIP
8-pin
S
■ OPTIMIZED FOR OFF-LINE CONTROL
■ LOW START-UP CURRENT (<1mA)
■ AUTOMATIC FEED FORWARD
COMPENSATION
■ TRIMMED OSCILLATOR DISCHARGE
CURRENT
■ PULSE-BY-PULSE CURRENT LIMITING
■ ENHANCED LOAD RESPONSE
CHARACTERISTICS
■ UNDER-VOLTAGE LOCKOUT WITH 6V
HYSTERESIS (SG1842 only)
■ DOUBLE-PULSE SUPPRESSION
■ HIGH-CURRENT TOTEM-POLE OUTPUT
(1AMP PEAK)
■ INTERNALLY TRIMMED BANDGAP
REFERENCE
■ 500KHZ OPERATION
■ UNDERVOLTAGE LOCKOUT
SG1842 - 16 volts
SG1843 - 8.4 volts
■ LOW SHOOT-THROUGH CURRENT <75mA
OVER TEMPERATURE
RST
AC
INPUT
A T A
K E Y F E AT U R E S
PRODUCT HIGHLIGHT
T Y P I C A L A P P L I C AT I O N
D
PA C K A G E O R D E R I N F O R M AT I O N
Plastic SOIC
Plastic SOIC
Ceramic DIP
Ceramic DIP
DM 8-pin
D 14-pin
Y 8-pin
J 14-pin
Cer. Flatpack
F 10-pin
Ceramic LCC
L 20-pin
SG3842M
SG3842N
SG3842DM
SG3842D
SG3842Y
SG3842J
—
—
SG3843M
SG3843N
SG3843DM
SG3843D
SG3843Y
SG3843J
—
—
SG2842M
SG2842N
SG2842DM
SG2842D
SG2842Y
SG2842J
—
—
SG2843M
SG2843N
SG2843DM
SG2843D
SG2843Y
SG2843J
—
—
—
—
—
—
SG1842Y
SG1842J
—
SG1842L
—
—
—
—
SG1843Y
SG1843J
—
SG1843L
—
—
—
—
SG1842Y/883B SG1842J/883B
—
SG1842L/883B
—
—
—
—
SG1843Y/883B SG1843J/883B
—
SG1843L/883B
—
—
—
—
SG1842Y/DESC SG1842J/DESC
SG1842F/DESC SG1842L/DESC
—
—
SG1843Y/DESC SG1843J/DESC
Note: All surface-mount packages are available in Tape & Reel.
SG1843F/DESC SG1843L/DESC
F O R F U R T H E R I N F O R M AT I O N C A L L ( 7 1 4 ) 8 9 8 - 8 1 2 1
Copyright © 2000
Rev. 1.6 4/00
11861 W ESTERN A VENUE , G ARDEN G ROVE , CA. 92841
1
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
A B S O L U T E M A X I M U M R AT I N G S
D
A T A
S
H E E T
PACKAGE PIN OUTS
(Notes 1 & 2)
Supply Voltage (ICC < 30mA) ............................................................... Self Limiting
Supply Voltage (Low Impedance Source) ........................................................ 30V
Output Current (Peak) ....................................................................................... ±1A
Output Current (Continuous) ....................................................................... 350mA
Output Energy (Capacitive Load) ....................................................................... 5µJ
Analog Inputs (Pins 2, 3) ................................................................. -0.3V to +6.3V
Error Amp Output Sink Current ..................................................................... 10mA
Power Dissipation at TA = 25°C (DIL-8) ............................................................ 1W
Operating Junction Temperature
Hermetic (J, Y, F, L Packages) ................................................................... 150°C
Plastic (N, M, D, DM Packages) ................................................................ 150°C
Storage Temperature Range .......................................................... -65°C to +150°C
Lead Temperature (Soldering, 10 Seconds) .................................................. 300°C
COMP
VFB
ISENSE
RT/CT
COMP
N.C.
VFB
N.C.
ISENSE
N.C.
RT/CT
95°C/W
COMP
N.C.
VFB
N.C.
ISENSE
N.C.
RT/CT
165°C/W
D PACKAGE:
120°C/W
Y PACKAGE:
130°C/W
80°C/W
F PACKAGE:
THERMAL RESISTANCE-JUNCTION TO CASE, θ JC
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
1
8
2
7
3
6
4
5
VREF
VCC
OUTPUT
GND
1
14
2
13
3
12
4
11
5
10
6
9
7
8
VREF
N.C.
VCC
VC
OUTPUT
GND
PWR GND
80°C/W
145°C/W
1
14
2
13
3
12
4
11
5
10
6
9
7
8
VREF
N.C.
VCC
VC
OUTPUT
GROUND
POWER GND
J & N PACKAGE
(Top View)
J PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
5
65°C/W
DM PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
6
4
D PACKAGE
(Top View)
N PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
3
VREF
VCC
OUTPUT
GND
DM PACKAGE
(Top View)
M PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
7
COMP
VFB
ISENSE
RT/CT
T H E R M A L D ATA
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
8
2
M & Y PACKAGE
(Top View)
Note 1. Exceeding these ratings could cause damage to the device.
Note 2. All voltages are with respect to Pin 5. All currents are positive into the specified
terminal.
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
1
1. COMP
2. VFB
3. ISENSE
4. RT/CT
5. POWER GND
1
2
3
4
5
10.VREF
9. VCC
8. VC
7. OUTPUT
6. GND
10
9
8
7
6
L PACKAGE:
THERMAL RESISTANCE-JUNCTION TO CASE, θ JC
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
F PACKAGE
(Top View)
35°C/W
120°C/W
Junction Temperature Calculation: TJ = TA + (PD x θJA).
The θJA numbers are guidelines for the thermal performance of the device/pc-board
system. All of the above assume no ambient airflow.
3
2
1 20 19
4
18
5
17
6
16
7
15
8
14
9 10 11 12 13
1. N.C.
2. COMP
3. N.C.
4. N.C.
5. VFB
6. N.C.
7. ISENSE
8. N.C.
9. N.C.
10. RT/CT
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
N.C.
GROUND
N.C.
N.C.
OUTPUT
N.C.
VCC
N.C.
N.C.
VREF
L PACKAGE
(Top View)
2
Copyright © 2000
Rev. 1.6 4/00
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
D
R O D U C T I O N
A T A
S
H E E T
R E C O M M E N D E D O P E R AT I N G C O N D I T I O N S
Parameter
Recommended Operating Conditions
Min.
Typ.
Max.
Symbol
Supply Voltage Range
Output Current (Peak)
Output Current (Continuous)
Analog Inputs (Pin 2, Pin 3)
Error Amp Output Sink Current
Oscillator Frequency Range
Oscillator Timing Resistor
Oscillator Timing Capacitor
Operating Ambient Temperature Range:
SG1842/43
SG2842/43
SG3842/43
Note 3. Range over which the device is functional.
(Note 3)
Units
30
±1
200
0.1
0.52
0.001
500
150
1.0
V
A
mA
V
mA
kHz
KΩ
µF
-55
-25
0
125
85
70
°C
°C
°C
0
2.6
5
RT
CT
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for SG1842/SG1843 with -55°C ≤ TA ≤ 125°C, SG2842/
SG2843 with -25°C ≤ TA ≤ 85°C, SG3842/SG3843 with 0°C ≤ TA ≤ 70°C, VCC = 15V (Note 7), RT = 10kΩ, and CT = 3.3nF. Low duty cycle pulse testing
techniques are used which maintains junction and case temperatures equal to the ambient temperature.)
Parameter
Symbol
Test Conditions
SG1842/43
SG2842/43
SG3842/43
Units
Min. Typ. Max. Min. Typ. Max. Min. Typ. Max.
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temperature Stability (Note 4)
Total Output Variation (Note 4)
Output Noise Voltage (Note 4)
Long Term Stability (Note 4)
Output Short Circuit
TJ = 25°C, IO = 1mA
12 ≤ VIN ≤ 25V
1 ≤ IO ≤ 20mA
VN
Line, Load, Temp.
10Hz ≤ f ≤ 10kHz, TJ = 25°C
TA = 125°C, 1000hrs
4.95 5.00 5.05 4.95 5.00 5.05 4.90 5.00 5.10
6
20
6
20
6
20
6
25
6
25
6
25
0.2 0.4
0.2 0.4
0.2 0.4
4.90
5.10 4.90
5.10 4.82
5.18
50
50
50
5
25
5
25
5
25
-30 -100 -180 -30 -100 -180 -30 -100 -180
V
mV
mV
mV/°C
V
µV
mV
mA
Oscillator Section
Initial Accuracy
Voltage Stability
Temperature Stability (Note 4)
Amplitude
Discharge Current
TJ = 25°C
12 ≤ VCC ≤ 25V
TMIN ≤ TA ≤ TMAX
VRT/CT (Peak to Peak)
TJ = 25°C
TMIN ≤ TA ≤ TMAX
47
9.3
9.5
kHz
%
%
V
mA
mA
2.45 2.50 2.55 2.45 2.50 2.55 2.42 2.50 2.58
-0.3 -1
-0.3
1
-0.3 -2
65
90
65
90
65
90
0.7
1
0.7
1
0.7
1
60
70
60
70
60
70
2
6
2
6
2
6
-0.5 -0.8
-0.5 -0.8
-0.5 -0.8
5
6
5
6
5
6
0.7 1.1
0.7 1.1
0.7 1.1
V
µA
dB
MHz
dB
mA
mA
V
V
7.8
7.0
52
0.2
5
1.7
8.3
57
1
47
8.8
9.0
7.5
7.2
52
0.2
5
1.7
8.4
57
1
47
9.3
9.5
7.5
7.2
52
0.2
5
1.7
8.4
57
1
Error Amp Section
Input Voltage
Input Bias Current
Open Loop Gain
Unity Gain Bandwidth (Note 4)
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
VOUT High
VOUT Low
VCOMP = 2.5V
AVOL
PSRR
2 ≤ VO ≤ 4V
TJ = 25°C
12 ≤ VCC ≤ 25V
VVFB = 2.7V, VCOMP = 1.1V
VVFB = 2.3V, VCOMP = 5V
VVFB = 2.3V, RL = 15K to gnd
VVFB = 2.7V, RL = 15K to VREF
(Electrical Characteristics continue next page.)
Copyright © 2000
Rev. 1.6 4/00
3
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
ELECTRICAL CHARACTERISTICS
Parameter
Symbol
Test Conditions
(Cont'd.)
SG1842/43
SG2842/43
SG3842/43
Units
Min. Typ. Max. Min. Typ. Max. Min. Typ. Max.
Current Sense Section
Gain (Notes 5 & 6)
Maximum Input Signal (Note 5)
Power Supply Rejection Ratio (Note 5) PSRR
Input Bias Current
Delay to Output (Note 4)
VCOMP = 5V
12 ≤ VCC ≤ 25V
2.85
0.9
3
1
70
-2
150
3.15 2.85
1.1 0.9
0.1
1.5
13.5
13.5
50
50
0.4
2.2
150
150
-10
300
3
1
70
-2
150
3.15 2.85
1.1 0.9
0.1
1.5
13.5
13.5
50
50
0.4
2.2
150
150
-10
300
3
1
70
-2
150
3.15
1.1
0.1
1.5
13.5
13.5
50
50
0.4
2.2
150
150
V
V
V
V
ns
ns
-10
300
V/V
V
dB
µA
ns
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
TJ = 25°C, CL = 1nF
13
12
1842
1843
1842
1843
15
7.8
9
7.0
16
8.4
10
7.6
17
9.0
11
8.3
15
7.8
9
7.0
16
8.4
10
7.6
17
9.0
11
8.2
14.5
7.8
8.5
7.0
16
8.4
10
7.6
17.5
9.0
11.5
8.2
V
V
V
V
93
95
100
0
90
95
100
0
90
95
100
0
%
%
0.5
11
34
1
17
13
12
13
12
Under-Voltage Lockout Section
Start Threshold
Min. Operation Voltage After Turn-On
PWM Section
Maximum Duty Cycle
Minimum Duty Cycle
Power Consumption Section
Start-Up Current
Operating Supply Current
VCC Zener Voltage
VFB = VISENSE = 0V
ICC = 25mA
Notes: 4. These parameters, although guaranteed, are not 100% tested in
production.
5. Parameter measured at trip point of latch with VVFB = 0.
4
0.5
1
0.5
1
mA
11
17
11
17
mA
34
34
V
∆ VCOMP
6. Gain defined as: A = ∆ V
; 0 ≤ VISENSE ≤ 0.8V.
ISENSE
7. Adjust VCC above the start threshold before setting at 15V.
Copyright © 2000
Rev. 1.6 4/00
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
D
R O D U C T I O N
A T A
S
H E E T
BLOCK DIAGRAM
VCC*
34V
UVLO
S/R
GROUND**
16V (1842)
8.4V (1843)
6V (1842)
0.8V (1843)
VREF
5.0V
50mA
5V
REF
INTERNAL
BIAS
2.5V
VREF
GOOD LOGIC
RT/CT
VC*
OSCILLATOR
OUTPUT
ERROR AMP
VFB
COMP
CURRENT SENSE
S
2R
R
R
1V
PWM
LATCH
POWER GROUND**
CURRENT SENSE
COMPARATOR
* - VCC and VC are internally connected for 8 pin packages.
** - POWER GROUND and GROUND are internally connected for 8 pin packages.
Copyright © 2000
Rev. 1.6 4/00
5
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
GRAPH / CURVE INDEX
H E E T
FIGURE INDEX
Characteristic Curves
Application Information
FIGURE #
FIGURE #
1.
DROPOUT VOLTAGE vs. TEMPERATURE
13. OSCILLATOR TIMING CIRCUIT
2.
OSCILLATOR TEMPERATURE STABILITY
14. OSCILLATOR FREQUENCY vs. RT FOR VARIOUS CT
3.
CURRENT SENSE TO OUTPUT DELAY vs. TEMPERATURE
4.
OUTPUT DUTY CYCLE vs. TEMPERATURE
5.
START-UP CURRENT vs. TEMPERATURE
FIGURE #
6.
REFERENCE VOLTAGE vs. TEMPERATURE
15. CURRENT SENSE SPIKE SUPPRESSION
7.
START-UP VOLTAGE THRESHOLD vs. TEMPERATURE
16. MOSFET PARASITIC OSCILLATIONS
8.
START-UP VOLTAGE THRESHOLD vs. TEMPERATURE
17. BIPOLAR TRANSISTOR DRIVE
9.
OSCILLATOR DISCHARGE CURRENT vs. TEMPERATURE
18. ISOLATED MOSFET DRIVE
Typical Applications Section
10. OUTPUT SATURATION VOLTAGE vs. OUTPUT CURRENT AND
TEMPERATURE (SINK TRANSISTOR)
19. ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL WITH
SOFTSTART
11. CURRENT SENSE THRESHOLD vs. ERROR AMPLIFIER OUTPUT
20. EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT
SYNCHRONIZATION
12. OUTPUT SATURATION VOLTAGE vs. OUTPUT CURRENT AND
TEMPERATURE (SOURCE TRANSISTOR)
21. OSCILLATOR CONNECTION
22. ERROR AMPLIFIER CONNECTION
23. SLOPE COMPENSATION
24. OPEN LOOP LABORATORY FIXTURE
25. OFF-LINE FLYBACK REGULATOR
6
Copyright © 2000
Rev. 1.6 4/00
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
CHARACTERISTIC CURVES
FIGURE 1. — DROPOUT VOLTAGE vs. TEMPERATURE
FIGURE 2. — OSCILLATOR TEMPERATURE STABILITY
VIN = 15V
Duty Cycle = 50%
0
10.0
SG1842
Frequency Drift - (%)
Minimum Operating Voltage - (V)
2
9.6
9.2
8.8
8.4
8.0
-75
-25
0
-4
-6
-8
-10
SG1843
-50
-2
25
50
75
100
-75
125
-50
-25
0
25
50
75
100
125
Junction Temperature - (°C)
Junction Temperature - (°C)
FIGURE 3. — CURRENT SENSE TO OUTPUT DELAY vs.
TEMPERATURE
FIGURE 4. — OUTPUT DUTY CYCLE vs. TEMPERATURE
200kHz
50
Output Duty Cycle - (%)
Current Sense Delay - (nS)
220
200
180
VPIN3 = 1.1V
160
140
120
-75
100kHz
50kHz
50kHz
48
47
100kHz
46
200kHz
45
44
-50
-25
0
25
50
75
Junction Temperature - (°C)
Copyright © 2000
Rev. 1.6 4/00
49
100
125
-75
-50
-25
0
25
50
75
100
125
Junction Temperature - (°C)
7
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
CHARACTERISTIC CURVES
FIGURE 5. — START-UP CURRENT vs. TEMPERATURE
FIGURE 6. — REFERENCE VOLTAGE vs. TEMPERATURE
5.02
0.7
5.01
Reference Voltage - (V)
Start-Up Current - (mA)
SG1842
0.6
0.5
0.4
0.3
SG1843
VCC = 15V
5.00
4.99
4.98
0.2
-75
-50
-25
0
25
50
75
100
-75
125
-50
-25
0
25
50
75
100
125
Junction Temperature - (°C)
Junction Temperature - (°C)
FIGURE 7. — START-UP VOLTAGE THRESHOLD vs.
TEMPERATURE
FIGURE 8. — START-UP VOLTAGE THRESHOLD vs.
TEMPERATURE
16.08
8.32
16.06
Start Up Voltage - (V)
Reference Voltage - (V)
SG1843
8.30
8.28
8.26
8.24
8.22
SG1842
16.04
16.02
16.00
8.20
8.18
-75
15.98
-50
-25
0
25
50
75
Junction Temperature - (°C)
8
100
125
-75
-50
-25
0
25
50
75
100
125
Junction Temperature - (°C)
Copyright © 2000
Rev. 1.6 4/00
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
CHARACTERISTIC CURVES
FIGURE 10. — OUTPUT SATURATION VOLTAGE vs.
OUTPUT CURRENT & TEMPERATURE
8.2
2.5
8.0
2.0
Saturation Voltage - (V)
Oscillator Discharge Current - (mA)
FIGURE 9. — OSCILLATOR DISCHARGE CURRENT vs.
TEMPERATURE
7.8
7.6
7.4
°C
+25
1.5
5°C
+12
1.0
VIN = 15V
Duty Cycle < 5%
0.5
7.2
-75
C
-55°
0
-50
-25
0
25
50
75
100
100
125
Junction Temperature - (°C)
200
300
400
500
Output Current - (mA)
FIGURE 11. — CURRENT SENSE THRESHOLD vs.
ERROR AMPLIFIER OUTPUT
FIGURE 12. — OUTPUT SATURATION VOLTAGE vs.
OUTPUT CURRENT & TEMPERATURE
1.0
0.8
VIN = 15V
Duty Cycle < 5%
Saturation Voltage - (V)
4.0
12
5°C
25
°C
-55
°C
Current Sense Threshold - (V)
0.9
0.7
0.6
0.5
0.4
0.3
0.2
3.0
°C
25
+1
5°C
+2
°C
-55
°C
+25
2.0
5°C
+12
1.0
0.1
0
0
1.0
2.0
3.0
4.0
Error Amp Output Voltage - (V)
Copyright © 2000
Rev. 1.6 4/00
5.0
100
200
300
400
500
Output Current - (mA)
9
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
D
R O D U C T I O N
A T A
S
H E E T
A P P L I C AT I O N I N F O R M AT I O N
OSCILLATOR
The oscillator of the 1842/43 family of PWM's is designed such
that many values of RT and CT will give the same oscillator
frequency, but only one combination will yield a specific duty
cycle at a given frequency.
A set of formulas are given to determine the values of RT and
CT for a given frequency and maximum duty cycle. (Note: These
formulas are less accurate for smaller duty cycles or higher
frequencies. This will require trimming of RT or CT to correct for
this error.)
Given: Frequency ≡ f
Maximum Duty Cycle ≡ Dm
Example:
A Flyback power supply requires a maximum of 45% duty
cycle at a switching frequency of 50kHz. What are the values
of RT and CT?
 (1.76)1/Dm -1 
Calculate: RT = 267 
(Ω)
(1-Dm)/Dm
- 1
 (1.76)
Given:
 (1.76)1/.045 -1 
Calculate: RT = 267  (1.76).55/.45 - 1  = 674Ω


where .3 < Dm < .95
CT =
1.86 * Dm
f * RT
f = 50kHz
Dm = 0.45
(µF)
CT =
1.86 * 0.45
= .025µF
50000 * 674
1000
For Duty-Cycles above 95% use:
VREF
RT =
680
RT =
2k
RT =
5k
RT =
10k
RT =
20k
RT =
30k
RT =
50k
RT =
7
RT = 0k
100
k
RT
RT/CT
CT
f - (kHz)
100
10
GND
1.86
F≈
RT CT
where RT ≥ 5kΩ
FIGURE 13 — OSCILLATOR TIMING CIRCUIT
10
1
.001
.002
.005
.01
.02
.05
0.1
CT Value - (µF)
FIGURE 14 — OSCILLATOR FREQUENCY vs. RT FOR VARIOUS CT
Copyright © 2000
Rev. 1.6 4/00
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
T Y P I C A L A P P L I C AT I O N C I R C U I T S
Pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package.
VCC
VIN
VIN
7 (12)
7 (12)
7 (11)
SG1842/43
VCC
7 (11)
Q1
Q1
R1
6 (10)
SG1842/43
6 (10)
IPK
5 (8)
R
IPK(MAX) = 1.0V
RS
3 (5)
RS
C
5 (8)
RS
3 (5)
FIGURE 16. — MOSFET PARASITIC OSCILLATIONS
FIGURE 15. — CURRENT-SENSE SPIKE SUPPRESSION
The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
A resistor (R1) in series with the MOSFET gate reduce overshoot and
ringing caused by the MOSFET input capacitance and any inductance in series with the gate drive. (Note: It is very important to
have a low inductance ground path to insure correct operation of
the I.C. This can be done by making the ground paths as short and
as wide as possible.)
VCC
IB
VC +
R2
VIN
VIN
Isolation
Boundary
7 (12)
VC1
R1|| R2 _
7 (11)
VC
VC1
6 (10)
Waveforms
7 (11)
R2
SG1842/43
Q1
6 (10)
SG1842/43
C1
R1
+
0
_
50% DC
5 (8)
Q1
+
R
0
_
3 (5)
C
5 (8)
3 (5)
RS
FIGURE 17. — BIPOLAR TRANSISTOR DRIVE
The 1842/43 output stage can provide negative base current to
remove base charge of power transistor (Q1) for faster turn off. This
is accomplished by adding a capacitor (C1) in parallel with a resistor
(R1). The resistor (R1) is to limit the base current during turn on.
Copyright © 2000
Rev. 1.6 4/00
RS
IPK =
V (PIN 1) - 1.4
3RS



NP
NS
NS
NP
25% DC



FIGURE 18. — ISOLATED MOSFET DRIVE
Current transformers can be used where isolation is required
between PWM and Primary ground. A drive transformer is then
necessary to interface the PWM output with the MOSFET.
11
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
T Y P I C A L A P P L I C AT I O N C I R C U I T S
VCC
(continued)
VIN
8 (14)
7 (12)
6 (10)
SG1842/43
1N4148
1 (1)
R1
SG1842/43
Q1
2 (3)
C
4
6
7 (11)
4 (7)
R2
8
RA
8 (14)
I
555
TIMER
RB
3
4 (7)
5 (8)
MPSA63
2
VCS
3 (5)
1
RS
5 (9)
5 (9)
To other
SGX842/43
VCS
 R1 
Where: VCS = 1.67 
 and VC.S.MAX = 1V (Typ.)
RS
 R1+R2 
 V - 1.3   R1 R2 
tSOFTSTART = -ln 1 - EAO R
  R +R  C
5  1 
1
2
IPK =

 R1+R 2 
 

f=
1.44
(RA + 2RB)C
f=
RB
RA + 2RB
where; VEAO ≡ voltage at the Error Amp Output under
minimum line and maximum load conditions.
FIGURE 19. — ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL
WITH SOFTSTART
Softstart and adjustable peak current can be done with the external
circuitry shown above.
2.8V
5V
FIGURE 20. — EXTERNAL DUTY CYCLE CLAMP AND
MULTI-UNIT SYNCHRONIZATION
Precision duty cycle limiting as well as synchronizing several 1842/
1843's is possible with the above circuitry.
8 (14)
1.1V
2.5V
RT
SG1842/43
0.5mA
4 (7)
2 (3)
CT
SG1842/43
Discharge
Current
Ri
RF
Id = 8.2mA
FIGURE 21. — OSCILLATOR CONNECTION
The oscillator is programmed by the values selected for the timing
components RT and CT. Refer to application information for
calculation of the component values.
12
1 (1)
RF 10K
FIGURE 22. — ERROR AMPLIFIER CONNECTION
Error amplifier is capable of sourcing and sinking current up to 0.5mA.
Copyright © 2000
Rev. 1.6 4/00
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
D
R O D U C T I O N
A T A
S
H E E T
T Y P I C A L A P P L I C AT I O N C I R C U I T S
(continued)
VCC
SG1842/43
VIN
7(12)
VO
5V
8(14)
5V
UVLO
S
5V
REF
R
RT
INTERNAL
BIAS
2.5V
2N222A
VREF
GOOD LOGIC
RSLOPE
7(11)
4(7)
Q1
OSCILLATOR
From VO
CT
Ri
Rd
2(3)
CF
1V
ERROR
AMP
RF
6(10)
C.S.
COMP
2R
R
5(8)
PWM
LATCH
R
3(5)
1(1)
5(9)
C
RS
FIGURE 23. — SLOPE COMPENSATION
Due to inherent instability of current mode converters running above 50% duty cycle, a slope compensation should be added to
either current sense pin or the error amplifier. Figure 23 shows a typical slope compensation technique.
VREF
RT
2N2222
4.7K
100K
1K
ERROR AMP
ADJUST
4.7K
5K
ISENSE
ADJUST
VCC
A
SG1842/43
1
COMP
VREF
8
2
VFB
VCC
7
3
ISENSE
OUTPUT
6
4
RTCT
GROUND
5
0.1µF
0.1µF
CT
1K
OUTPUT
GROUND
FIGURE 24. — OPEN LOOP LABORATORY FIXTURE
High-peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be
connected to pin 5 in a single point ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply
an adjustable ramp to pin 3.
Copyright © 2000
Rev. 1.6 4/00
13
PRODUCT DATABOOK 1996/1997
SG1842/SG1843 Series
CURRENT-MODE PWM CONTROLLER
P
R O D U C T I O N
D
A T A
S
H E E T
T Y P I C A L A P P L I C AT I O N C I R C U I T S
(continued)
TI
4.7 1W
220µF
250V
673-3
USD735
0.01pF
400V
56k
1W
5V
2-5A
4700µF
10V
1N3613
AC
INPUT
1N3613
16V
SG1842
150k
3.6k
COMP
0.01µF
27
OUT
20k
100pF
VREF
10k
RT/CT
0.01µF
820pF
1N3613
VCC
VFB
10µF
20V
UFN432
20k
CUR
SEN
GND
2.5k
T1: Coilcraft E - 4140 - b
Primary - 97 turns
single AWG 24
Secondary - 4 turns
4 parallel AWG 22
Control - 9 turns
3 parallel AWG 28
1k
470pF
0.85
.0047µF
ISOLATION
BOUNDARY
FIGURE 25. — OFF-LINE FLYBACK REGULATOR
SPECIFICATIONS
Input line voltage:
Input frequency:
Switching frequency:
Output power:
Output voltage:
Output current:
Line regulation:
Load regulation:
Efficiency @ 25 Watts,
VIN = 90VAC:
VIN = 130VAC:
Output short-circuit current:
14
90VAC to 130VAC
50 or 60Hz
40KHz ±10%
25W maximum
5V +5%
2 to 5A
0.01%/V
8%/A*
* This circuit uses a low-cost feedback scheme in which the DC
voltage developed from the primary-side control winding is
sensed by the SG1842 error amplifier. Load regulation is
therefore dependent on the coupling between secondary
and control windings, and on transformer leakage
inductance.
70%
65%
2.5Amp average
Copyright © 2000
Rev. 1.6 4/00