LINFINITY SG1842, SG1843 DATA SHEET

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LIN DOC #: 1842

SG1842/SG1843 Series

C

URRENT MODE

PWM C

ONTROLLER

T HE I NFINITE P OWER OF I NNOVATION

DESCRIPTION KEY FEATURES

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-

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.

PRODUCT HIGHLIGHT

TYPICAL APPLICATION OF SG3842 IN A FLYBACK CONVERTER

R

AC

INPUT

I

V

CC

SG3842

ST

P RODUCTION DATA SHEET

■ 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

ST

HIGH RELIABILITY FEATURES

■ AVAILABLE TO MIL-STD-883B AND DESC

SMD

■ SCHEDULED FOR MIL-M38510 QPL LISTING

■ RADIATION DATA AVAILABLE

■

LINFINITY LEVEL "S" PROCESSING AVAILABLE

(°C)

T

A

0 to 70

-25 to 85

-55 to 125

MIL-STD/883

DESC

Copyright © 2000
Rev. 1.6 4/00

PACKAGE ORDER INFORMATION

Plastic DIP

M

8-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

Plastic DIP

N

14-pin

Plastic SOIC

DM

8-pin

— — SG1843Y/DESC SG1843J/DESC SG1843F/DESC SG1843L/DESC

Note: All surface-mount packages are available in Tape & Reel.

Plastic SOIC

D

14-pin

Ceramic DIP

Y

8-pin

Ceramic DIP

J

14-pin

Cer. Flatpack

F

10-pin

L

FOR FURTHER INFORMATION CALL [phone]

11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841

Ceramic LCC
20-pin

1

PRODUCT DATABOOK 1996/1997

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

PWM C

ONTROLLER

ABSOLUTE MAXIMUM RATINGS (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

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 DATA

M PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

N PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

DM PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

D PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

Y PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

J PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

F PACKAGE:

THERMAL RESISTANCE-JUNCTION TO CASE,

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

L PACKAGE:

THERMAL RESISTANCE-JUNCTION TO CASE,

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

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.

θθ

θ

θθ

JA

θθ

θ

θθ

JA

θθ

θ

θθ

JA

θθ

θ

θθ

JA

θθ

θ

θθ

JA

θθ

θ

θθ

JA

θθ

θ

θθ

JC

θθ

θ

θθ

JA

θθ

θ

θθ

JC

θθ

θ

θθ

JA

95°C/W

65°C/W

165°C/W

120°C/W

130°C/W

80°C/W

80°C/W

145°C/W

35°C/W

120°C/W

1. COMP

2. V

FB

3. I

SENSE

4. RT/C

T

5. POWER GND

32

4

5

6

7

8

91110

PACKAGE PIN OUTS

1 8

COMP

27

V

FB

36

I

SENSE

45

RT/C

T

M & Y PACKAGE

(Top View)

SENSE

V

FB

T

1 8

27

36

45

COMP

I

RT/C

DM PACKAGE

(Top View)

N.C.

V
N.C.
I

SENSE

N.C.

FB

T

1 14

213

312

411

510

69

78

COMP

RT/C

D PACKAGE

(Top View)

1 14

COMP

213

N.C.

312

V

FB

411

N.C.

510

I

SENSE

69

N.C.

78

RT/C

T

J & N PACKAGE

(Top View)

1 10
29
38
47
56

F PACKAGE

(Top View)

12019

12 13

L PACKAGE

(Top View)

V

REF

V

CC

OUTPUT
GND

V

REF

V

CC

OUTPUT
GND

V

REF

N.C.
V

CC

V

C

OUTPUT
GND
PWR GND

V

REF

N.C.
V

CC

V

C

OUTPUT
GROUND
POWER GND

1. N.C.

2. COMP

3. N.C.

18

4. N.C.

17

5. V

16

15

14

FB

6. N.C.

7. I

SENSE

8. N.C.

9. N.C.

10. RT/C

T

10.V

REF

9. V

CC

8. V

C

7. OUTPUT

6. GND

11. N.C.

12. GROUND

13. N.C.

14. N.C.

15. OUTPUT

16. N.C.

17. V

CC

18. N.C.

19. N.C.

20. V

REF

2

Copyright © 2000

Rev. 1.6 4/00

PRODUCT DATABOOK 1996/1997

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

RECOMMENDED OPERATING CONDITIONS (Note 3)

PWM C

ONTROLLER

Parameter

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 R
Oscillator Timing Capacitor C

T

T

Recommended Operating Conditions

Min. Typ. Max.

Units

30 V
±1 A

200 mA

02.6V
5mA

0.1 500 kHz

0.52 150 KΩ

0.001 1.0 µF

Operating Ambient Temperature Range:

SG1842/43
SG2842/43
SG3842/43

-55 125 °C

-25 85 °C
070°C

Note 3. Range over which the device is functional.

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

Min. Typ. Max. Min. Typ. Max. Min. Typ. Max.

SG3842/43

Units

Reference Section

Output Voltage TJ = 25°C, IO = 1mA
Line Regulation 12 ≤ VIN ≤ 25V
Load Regulation 1 ≤ IO ≤ 20mA
Temperature Stability (Note 4)
Total Output Variation (Note 4) Line, Load, Temp.
Output Noise Voltage (Note 4) VN10Hz ≤ f ≤ 10kHz, TJ = 25°C
Long Term Stability (Note 4) TA = 125°C, 1000hrs
Output Short Circuit

4.95 5.00 5.05 4.95 5.00 5.05 4.90 5.00 5.10 V
620 620 620 mV
625 625 625 mV

0.2 0.4 0.2 0.4 0.2 0.4 mV/°C

4.90 5.10 4.90 5.10 4.82 5.18 V

50 50 50 µV

525 525 525 mV

-30 -100 -180 -30 -100 -180 -30 -100 -180 mA

Oscillator Section

Initial Accuracy TJ = 25°C
Voltage Stability 12 ≤ VCC ≤ 25V
Temperature Stability (Note 4) T
Amplitude V

≤ TA ≤ T

MIN

(Peak to Peak)

RT/CT

MAX

Discharge Current TJ = 25°C

T

≤ TA ≤ T

MIN

MAX

47 52 57 47 52 57 47 52 57 kHz

0.2 1 0.2 1 0.2 1 %
555%

1.7 1.7 1.7 V

7.8 8.3 8.8 7.5 8.4 9.3 7.5 8.4 9.3 mA

7.0 9.0 7.2 9.5 7.2 9.5 mA

Error Amp Section

Input Voltage V
Input Bias Current
Open Loop Gain A

VOL

Unity Gain Bandwidth (Note 4) TJ = 25°C
Power Supply Rejection Ratio PSRR 12 ≤ VCC ≤ 25V
Output Sink Current V
Output Source Current V
V

High V

OUT

V

Low V

OUT

= 2.5V

COMP

2 ≤ VO ≤ 4V

= 2.7V, V

VFB

= 2.3V, V

VFB

= 2.3V, RL = 15K to gnd

VFB

= 2.7V, RL = 15K to V

VFB

COMP

COMP

= 1.1V
= 5V

2.45 2.50 2.55 2.45 2.50 2.55 2.42 2.50 2.58 V

-0.3 -1 -0.3 1 -0.3 -2 µA

65 90 65 90 65 90 dB

0.7 1 0.7 1 0.7 1 MHz
60 70 60 70 60 70 dB

26 26 26 mA

-0.5 -0.8 -0.5 -0.8 -0.5 -0.8 mA
56 56 56 V

REF

0.7 1.1 0.7 1.1 0.7 1.1 V

(Electrical Characteristics continue next page.)

Copyright © 2000
Rev. 1.6 4/00

3

PRODUCT DATABOOK 1996/1997

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS (Cont'd.)

PWM C

ONTROLLER

Parameter

Symbol

Test Conditions

Current Sense Section

Gain (Notes 5 & 6)
Maximum Input Signal (Note 5) V
Power Supply Rejection Ratio (Note 5) PSRR 12 ≤ V
Input Bias Current
Delay to Output (Note 4)

COMP

= 5V

CC

≤ 25V

Output Section

Output Low Level I

Output High Level I

Rise Time TJ = 25°C, CL = 1nF
Fall Time TJ = 25°C, CL = 1nF

= 20mA

SINK

I

= 200mA

SINK

SOURCE

I

SOURCE

= 20mA
= 200mA

Under-Voltage Lockout Section

Start Threshold 1842

1843

Min. Operation Voltage After Turn-On 1842

1843

PWM Section

Maximum Duty Cycle
Minimum Duty Cycle

Power Consumption Section

Start-Up Current
Operating Supply Current VFB = V
VCC Zener Voltage ICC = 25mA

Notes: 4. These parameters, although guaranteed, are not 100% tested in

production.

5. Parameter measured at trip point of latch with V

ISENSE

VFB

= 0V

= 0.

SG1842/43

SG2842/43

Min. Typ. Max. Min. Typ. Max. Min. Typ. Max.

2.85 3 3.15 2.85 3 3.15 2.85 3 3.15 V/V

0.9 1 1.1 0.9 1 1.1 0.9 1 1.1 V
70 70 70 dB

-2 -10 -2 -10 -2 -10 µA

150 300 150 300 150 300 ns

0.1 0.4 0.1 0.4 0.1 0.4 V

1.5 2.2 1.5 2.2 1.5 2.2 V
13 13.5 13 13.5 13 13.5 V
12 13.5 12 13.5 12 13.5 V

50 150 50 150 50 150 ns
50 150 50 150 50 150 ns

15 16 17 15 16 17 14.5 16 17.5 V

7.8 8.4 9.0 7.8 8.4 9.0 7.8 8.4 9.0 V
9 10 11 9 10 11 8.5 10 11.5 V

7.0 7.6 8.3 7.0 7.6 8.2 7.0 7.6 8.2 V

93 95 100 90 95 100 90 95 100 %

000%

0.5 1 0.5 1 0.5 1 mA
11 17 11 17 11 17 mA
34 34 34 V

∆ V

6. Gain defined as: A = ; 0 ≤ V

7. Adjust VCC above the start threshold before setting at 15V.

∆ V

COMP

ISENSE

SG3842/43

≤ 0.8V.

ISENSE

Units

4

Copyright © 2000

Rev. 1.6 4/00

V

CC

GROUND**

PRODUCT DATABOOK 1996/1997

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

BLOCK DIAGRAM

*

34V

16V (1842)

8.4V (1843)

2.5V

UVLO

6V (1842)

0.8V (1843)

PWM C

S / R

V

REF

GOOD LOGIC

ONTROLLER

5V

REF

INTERNAL

BIAS

V

REF

5.0V
50mA

V

*

C

R

T/CT

V

FB

COMP

CURRENT SENSE

- V

and VC are internally connected for 8 pin packages.

*

CC

- POWER GROUND and GROUND are internally connected for 8 pin packages.

**

OSCILLATOR

ERROR AMP

2R

R

1V

S

R

CURRENT SENSE
COMPARATOR

PWM
LATCH

OUTPUT

POWER GROUND**

Copyright © 2000
Rev. 1.6 4/00

5

PRODUCT DATABOOK 1996/1997

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

PWM C

ONTROLLER

GRAPH / CURVE INDEX

Characteristic Curves

FIGURE #

1. DROPOUT VOLTAGE vs. TEMPERATURE

2. OSCILLATOR TEMPERATURE STABILITY

3. CURRENT SENSE TO OUTPUT DELAY vs. TEMPERATURE

4. OUTPUT DUTY CYCLE vs. TEMPERATURE

5. START-UP CURRENT vs. TEMPERATURE

6. REFERENCE VOLTAGE vs. TEMPERATURE

7. START-UP VOLTAGE THRESHOLD vs. TEMPERATURE

8. START-UP VOLTAGE THRESHOLD vs. TEMPERATURE

9. OSCILLATOR DISCHARGE CURRENT vs. TEMPERATURE

10. OUTPUT SATURATION VOLTAGE vs. OUTPUT CURRENT AND

TEMPERATURE (SINK TRANSISTOR)

11. CURRENT SENSE THRESHOLD vs. ERROR AMPLIFIER OUTPUT

12. OUTPUT SATURATION VOLTAGE vs. OUTPUT CURRENT AND

TEMPERATURE (SOURCE TRANSISTOR)

FIGURE INDEX

Application Information

FIGURE #

13. OSCILLATOR TIMING CIRCUIT

14. OSCILLATOR FREQUENCY vs. R

FOR VARIOUS C

T

T

Typical Applications Section

FIGURE #

15. CURRENT SENSE SPIKE SUPPRESSION

16. MOSFET PARASITIC OSCILLATIONS

17. BIPOLAR TRANSISTOR DRIVE

18. ISOLATED MOSFET DRIVE

19. ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL WITH

SOFTSTART

20. EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT

SYNCHRONIZATION

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

C

URRENT-MODE

P RODUCTION DATA SHEET

CHARACTERISTIC CURVES

PWM C

ONTROLLER

FIGURE 1. — DROPOUT VOLTAGE vs. TEMPERATURE

10.0

SG1842

9.6

9.2

8.8

8.4

Minimum Operating Voltage - (V)

8.0

-50-25 0255075100125

-75

SG1843

Junction Temperature - (°C)

FIGURE 3. — CURRENT SENSE TO OUTPUT DELAY vs.

TEMPERATURE

FIGURE 2. — OSCILLATOR TEMPERATURE STABILITY

2

0

-2

-4

-6

-8

Frequency Drift - (%)

-10

-50-25 0255075100125

-75

VIN = 15V
Duty Cycle = 50%

Junction Temperature - (°C)

FIGURE 4. — OUTPUT DUTY CYCLE vs. TEMPERATURE

Current Sense Delay - (nS)

Copyright © 2000
Rev. 1.6 4/00

220

200

180

160

140

120

V

PIN3

-50-25 0255075100125

-75

Junction Temperature - (°C)

= 1.1V

200kHz

50

49

48

47

46

45

Output Duty Cycle - (%)

44

-50-25 0255075100125

-75

100kHz
50kHz

Junction Temperature - (°C)

50kHz

100kHz
200kHz

7

PRODUCT DATABOOK 1996/1997

Junction Temperature - (°C)

Start Up Voltage - (V)

16.00

-75

-50-25 0255075100125

SG1842

16.02

16.04

16.06

16.08

15.98

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

CHARACTERISTIC CURVES

PWM C

ONTROLLER

FIGURE 5. — START-UP CURRENT vs. TEMPERATURE

0.7

SG1842

0.6

0.5

0.4

0.3

Start-Up Current - (mA)

0.2

-50-25 0255075100125

-75

SG1843

Junction Temperature - (°C)

FIGURE 7. — START-UP VOLTAGE THRESHOLD vs.

TEMPERATURE

FIGURE 6. — REFERENCE VOLTAGE vs. TEMPERATURE

5.02

5.01

VCC = 15V

5.00

4.99

Reference Voltage - (V)

4.98

-75

-50-25 0255075100125

Junction Temperature - (°C)

FIGURE 8. — START-UP VOLTAGE THRESHOLD vs.

TEMPERATURE

8.32

8.30

8.28

8.26

8.24

Reference Voltage - (V)

8.22

8.20

8.18

8

SG1843

-75

-50-25 0255075100125

Junction Temperature - (°C)

Copyright © 2000

Rev. 1.6 4/00

PRODUCT DATABOOK 1996/1997

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

CHARACTERISTIC CURVES

PWM C

ONTROLLER

FIGURE 9. — OSCILLATOR DISCHARGE CURRENT vs.

TEMPERATURE

8.2

8.0

7.8

7.6

7.4

Oscillator Discharge Current - (mA)

7.2

-75

-50-25 0255075100125

Junction Temperature - (°C)

FIGURE 11. — CURRENT SENSE THRESHOLD vs.

ERROR AMPLIFIER OUTPUT

1.0

FIGURE 10. — OUTPUT SATURATION VOLTAGE vs.

OUTPUT CURRENT & TEMPERATURE

2.5

2.0

1.5

1.0

Saturation Voltage - (V)

0.5

0

100 200 300 400 500

-55°C

+25°C

+125°C

VIN = 15V
Duty Cycle < 5%

Output Current - (mA)

FIGURE 12. — OUTPUT SATURATION VOLTAGE vs.

OUTPUT CURRENT & TEMPERATURE

Current Sense Threshold - (V)

Copyright © 2000
Rev. 1.6 4/00

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

4.0

125°C

25°C

-55°C

3.0

2.0

Saturation Voltage - (V)

1.0

0

1.0 2.0 3.0 4.0 5.0

0

Error Amp Output Voltage - (V)

VIN = 15V

Duty Cycle < 5%

+125°C

+25°C

-55°C

+25°C

+125°C

100 200 300 400 500

Output Current - (mA)

9

PRODUCT DATABOOK 1996/1997

T

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

APPLICATION INFORMATION

OSCILLATOR

The oscillator of the 1842/43 family of PWM's is designed such
that many values of R
frequency, but only one combination will yield a specific duty
cycle at a given frequency.

Given: Frequency ≡ f

Maximum Duty Cycle ≡ D

Calculate: RT = 267 (Ω)

CT = (µF)

For Duty-Cycles above 95% use:

and CT will give the same oscillator

T

m

1/D

(1-Dm)/D

m



-1



m

- 1






(1.76)



(1.76)

where .3 < Dm < .95

1.86 * D
f * R

V

RT/C

T

REF

m

RT

T

C

GND

PWM C

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.)

Example:

cycle at a switching frequency of 50kHz. What are the values
of RT and CT?

Given: f = 50kHz

Calculate: RT = 267 = 674Ω

1000

100

f - (kHz)

10

ONTROLLER

A set of formulas are given to determine the values of RT and

A Flyback power supply requires a maximum of 45% duty

Dm = 0.45

1/.045



(1.76)



.55/.45

(1.76)



1.86 * 0.45

CT = = .025µF

50000 * 674

R

= 680

T



R

= 2k

T



R

= 5k

T



R

= 10k

T



R

= 20k

T



R

= 30k

T



R

= 50k

T



R

= 70k

T



R

= 100k

T



-1

- 1





10

1.86

F ≈ where RT ≥ 5kΩ

R

TCT

FIGURE 13 — OSCILLATOR TIMING CIRCUIT

1

.001

.002 .02

.005 .01 .05 0.1

CT Value - (µF)

FIGURE 14 — OSCILLATOR FREQUENCY vs. RT FOR VARIOUS C

T

Copyright © 2000

Rev. 1.6 4/00

PRODUCT DATABOOK 1996/1997

VINV

CC

7 (12)

7 (11)

6 (10)

5 (8)

R

S

Q1

SG1842/43

3 (5)

R

1



V

CC

V

IN

7 (12)

7 (11)

6 (10)

5 (8)

3 (5)

SG1842/43

Isolation

Boundary

C

R

R

S

N

S

N

P

Q1

Waveforms

+
_

0

+
_

0

50% DC

25% DC

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS

Pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package.

VCCV

IN

7 (12)

PWM C

ONTROLLER

SG1842/43

7 (11)

6 (10)

5 (8)

3 (5)

Q1

I

PK

R

1.0V

I

=

PK(MAX)

R

R

C

S

S

FIGURE 15. — CURRENT-SENSE SPIKE SUPPRESSION

The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.

I

B

V

C

+



R

2

V

C1

_

R1|| R

2

SG1842/43

V

C

7 (11)

6 (10)

V

C

R

2

R

V

IN

C1

1

Q1

1

FIGURE 16. — MOSFET PARASITIC OSCILLATIONS

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.)

5 (8)

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

3 (5)





R

S

V (PIN 1) - 1.4

IPK =

3R

S

N

P





N

S





FIGURE 18. — ISOLATED MOSFET DRIVEFIGURE 17. — BIPOLAR TRANSISTOR 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

A

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

PWM C

ONTROLLER

V

7 (12)

8 (14)

4 (7)

2 (3)

1 (1)

R

2

1N4148

C

IPK = Where: VCS = 1.67 and V

t

SOFTSTART

where; V
minimum line and maximum load conditions.

MPSA63

R

1

V

CS

R

S



= -ln 1 - C




≡ voltage at the Error Amp Output under

EAO

V

EAO



5




SG1842/43

5 (9)

R




R1+R



- 1.3

R1+R









R



1









2

1

2

R1 R

R1+R





7 (11)

6 (10)

5 (8)

3 (5)

C.S.MAX



2



2



CC

= 1V (Typ.)

V

IN

Q1

I

V

CS

R

S

FIGURE 19. — ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL

WITH SOFTSTART

Softstart and adjustable peak current can be done with the external
circuitry shown above.

8 (14)

R

A

84

6

SG1842/43

R

B

2

f =

(RA + 2RB)C

f =

RA + 2R

1.44

R

B

555

TIMER

1

B

4 (7)

3

To other

SGX842/43

5 (9)

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.

5V

2.8V

1.1V

8 (14)

R

T

4 (7)

C

SG1842/43

Discharge

Current

I

= 8.2mA

d

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

2.5V
SG1842/43

0.5m

R

 10K

F

2 (3)

1 (1)

R

F

T

R

i

FIGURE 22. — ERROR AMPLIFIER CONNECTIONFIGURE 21. — OSCILLATOR 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

A

D

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

PWM C

ONTROLLER

V

CC

V

IN

From V

2N222A

O

R

i

R

d

SG1842/43

5V

8(14)

R

T

R

SLOPE

C

4(7)

C

T

2(3)

R

F

F

1(1)

OSCILLATOR

ERROR

AMP

2.5V

UVLO

2R

R5VREF

R

5(9)

S

V

REF

GOOD LOGIC

1V

C.S.

COMP

PWM

LATCH

5V

INTERNAL

BIAS

7(12)

7(11)

6(10)

5(8)

3(5)

Q1

R

CR

S

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.

V

O

V

REF

R

4.7K

ERROR AMP

DJUST

4.7K

T

COMP

1

V

2

I

3

RTC

4

SG1842/43

FB

SENSE

T

V

V

OUTPUT

GROUND

C

T

8

REF

7

CC

0.1µF 0.1µF

6

5

2N2222

100K

1K

5K

I

SENSE

ADJUST

A

1K

V

CC

OUTPUT

GROUN

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

Copyright © 2000
Rev. 1.6 4/00

an adjustable ramp to pin 3.

13

PRODUCT DATABOOK 1996/1997

A

SG1842/SG1843 Series

C

URRENT-MODE

P RODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

PWM C

ONTROLLER

AC

INPUT

3.6k

4.7 1W

220µF
250V

673-3

16V

20k

150k



100pF

10k

.0047µF0.01µF

SG1842

V

FB

COMP

V

REF

RT/C

T

V

CC

GND

56k
1W

OUT

CUR
SEN



1N3613

10µF

1k

470pF

20V



0.01µF

27

20k





0.01pF
400V

1N3613

UFN432

0.85

820pF

1N3613



2.5k



TI

ISOLATION

BOUNDARY

USD 735

4700µF

10V

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

5V

2-5

14

FIGURE 25. — OFF-LINE FLYBACK REGULATOR

SPECIFICATIONS

Input line voltage: 90VAC to 130VAC
Input frequency: 50 or 60Hz
Switching frequency: 40KHz ±10%
Output power: 25W maximum
Output voltage: 5V +5%
Output current: 2 to 5A
Line regulation: 0.01%/V
Load regulation: 8%/A*
Efficiency @ 25 Watts,

VIN = 90VAC: 70%
VIN = 130VAC: 65%

Output short-circuit current: 2.5Amp average

* 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.

Copyright © 2000

Rev. 1.6 4/00