5962-8670402PA - MICROSEMI - Datasheet.Directory

PRODUCTION DATA SHEET

Microsemi

Analog Mixed Signal Group

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

SG1842/SG1843 Series

CURRENT MODE PWM CONTROLLER

Rev. 1.6b 2010-03-15

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-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.

IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com

PRODUCT HIGHLIGHT

INPUT

SG3842

KEY FEATURES

 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

HIGH RELIABILITY

FEATURES

 AVAILABLE TO MIL-STD-883B AND

DSCC

 SCHEDULED FOR MIL-M38510

QPL LISTING

 RADIATION DATA AVAILABLE

 Microsemi LEVEL "S" PROCESSING

AVAILABLE

PACKAGE ORDER INFO

M Plastic DIP

8-Pin N Plastic DIP

14-Pin DM Plastic SOIC

8-Pin D Plastic SOIC

14-Pin Y Ceramic Dip

8-Pin J Ceramic DIP

14-Pin F Cer Flatpack

10-Pin L Ceramic LCC

20-Pin

TA (°C) RoHS / Pb-free Transition DC: 0503 RoHS / Pb-free Transition DC:0440

SG3842M SG3842N SG3842DM SG3842D SG3842Y SG3842J

0 to 70 SG3843M SG3843N SG3843DM SG3843D SG3843Y SG3842J

SG2842M SG2842N SG2842DM SG2842D SG2842Y SG2842J

-25 to 85 SG2843M SG2843N SG2843DM SG2843D SG2843Y SG2843J

SG1842Y SG1842J SG1842F SG1842L -55 to

125 SG1843Y SG1843J SG1843F SG1842L

SG1842Y/883B SG1842J/883B SG1842F/883B SG1842L/883B MIL-

STD/883 SG1843Y/883B SG1843J/883B SG1843F/883B SG1843L/883B

SG1842Y/DESC SG1842J/DESC SG1842F/DESC SG1842L/DESC

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

Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. SG2843DM-TR)

Plastic packages are RoHS compliant

TM ®

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PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

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

PACKAGE PIN OUTS

VREF

VCC

OUTPUT

GND

COMP

VFB

ISENSE

RT/CT

1 8

M & Y PACKAGE

(Top View)

DM PACKAGE

(Top View)

VREF

VCC

OUTPUT

GND

COMP

VFB

ISENSE

RT/CT

1 8

VREF

N.C.

VCC

OUTPUT

GND

PWR GND

COMP

N.C.

VFB

N.C.

ISENSE

N.C.

RT/CT

1 14

213

312

411

510

D PACKAGE

(Top View)

M PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 95°C/W

N PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 65°C/W

DM PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 165°C/W

D PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 120°C/W

Y PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 130°C/W

J PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 80°C/W

F PACKAGE:

THERMAL RESISTANCE-JUNCTION TO CASE, θθ

θθ

θJC 80°C/W

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 145°C/W

L PACKAGE:

THERMAL RESISTANCE-JUNCTION TO CASE, θθ

θθ

θJC 35°C/W

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θθ

θθ

θJA 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.

THERMAL DATA

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.

1 14

213

312

411

510

J & N PACKAGE

(Top View)

COMP

N.C.

VFB

N.C.

ISENSE

N.C.

RT/CT

VREF

N.C.

VCC

OUTPUT

GROUND

POWER GND

F PACKAGE

(Top View)

10.VREF

9. VCC

8. VC

7. OUTPUT

6. GND

1. COMP

2. VFB

3. ISENSE

4. RT/CT

5. POWER GND

1 10

L PACKAGE

(Top View)

91110

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

12019

12 13

11. N.C.

12. GROUND

13. N.C.

14. N.C.

15. OUTPUT

16. N.C.

17. VCC

18. N.C.

19. N.C.

20. VREF

Pb-free / RoHS Peak Package Solder Reflow Temp. (40 second max. exposure)........ 260°C (+0, -5)Pb-free / RoHS 100% Matte Tin Lead Finish

Pb-free / RoHS 100% Matte Tin Lead Finish

N Package: Pb-free / RoHS 100% Matte Tin Lead Finish

M Package: Pb-free / RoHS 100% Matte Tin Lead Finish

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ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS

(Unless otherwise specified, these specifications apply over the operating ambient temperatures for SG1842/SG1843 with -55°C ≤ T

≤ 125°C, SG2842/

SG2843 with -25°C ≤ T

≤ 85°C, SG3842/SG3843 with 0°C ≤ T

≤ 70°C, V

= 15V (Note 7), R

= 10kΩ, and C

= 3.3nF. Low duty cycle pulse testing

techniques are used which maintains junction and case temperatures equal to the ambient temperature.)

Reference Section

Parameter

Symbol

Test Conditions

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

SG3842/43

Units

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

SG2842/43

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) TMIN ≤ TA ≤ TMAX

Amplitude VRT/CT (Peak to Peak)

Discharge Current TJ = 25°C

TMIN ≤ TA ≤ TMAX

Error Amp Section

Input Voltage VCOMP = 2.5V

Input Bias Current

Open Loop Gain AVOL 2 ≤ VO ≤ 4V

Unity Gain Bandwidth (Note 4) TJ = 25°C

Power Supply Rejection Ratio PSRR 12 ≤ VCC ≤ 25V

Output Sink Current VVFB = 2.7V, VCOMP = 1.1V

Output Source Current VVFB = 2.3V, VCOMP = 5V

VOUT High VVFB = 2.3V, RL = 15K to gnd

VOUT Low VVFB = 2.7V, RL = 15K to VREF

SG1842/43

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

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

0.7 1.1 0.7 1.1 0.7 1.1 V

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 RT

Oscillator Timing Capacitor CT

Operating Ambient Temperature Range:

SG1842/43

SG2842/43

SG3842/43

RECOMMENDED OPERATING CONDITIONS (Note 3)

Parameter

Symbol

Units

Recommended Operating Conditions

Min. Typ. Max.

30 V

±1 A

200 mA

02.6V

5mA

0.1 500 kHz

0.52 150 KΩ

0.001 1.0 µF

-55 125 °C

-25 85 °C

070°C

Note 3. Range over which the device is functional.

(Electrical Characteristics continue next page.)

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PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS (Cont'd.)

Under-Voltage Lockout Section

Parameter

Symbol

Test Conditions

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 = VISENSE = 0V

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 VVFB = 0.

SG3842/43

Units

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

SG2842/43

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

SG1842/43

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

6. Gain defined as: A = ; 0 ≤ VISENSE ≤ 0.8V.

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

Output Low Level ISINK = 20mA

ISINK = 200mA

Output High Level ISOURCE = 20mA

ISOURCE = 200mA

Rise Time TJ = 25°C, CL = 1nF

Fall Time TJ = 25°C, CL = 1nF

Current Sense Section

Gain (Notes 5 & 6)

Maximum Input Signal (Note 5) VCOMP = 5V

Power Supply Rejection Ratio (Note 5) PSRR 12 ≤ VCC ≤ 25V

Input Bias Current

Delay to Output (Note 4)

Output Section

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

∆ VCOMP

∆ VISENSE

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ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

BLOCK DIAGRAM

*- VCC and VC are internally connected for 8 pin packages.

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

OSCILLATOR

REF

GOOD LOGIC

INTERNAL

BIAS

S / R 5V

REF

PWM

LATCH

CURRENT SENSE

COMPARATOR

ERROR AMP

UVLO

34V

GROUND**

COMP

CURRENT SENSE

POWER GROUND**

OUTPUT

REF

5.0V

50mA

16V (1842)

8.4V (1843)

6V (1842)

0.8V (1843)

2.5V

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PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

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. RT FOR VARIOUS CT

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

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ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

CHARACTERISTIC CURVES

FIGURE 2. — OSCILLATOR TEMPERATURE STABILITY

FIGURE 3. — CURRENT SENSE TO OUTPUT DELAY vs.

TEMPERATURE

FIGURE 4. — OUTPUT DUTY CYCLE vs. TEMPERATURE

FIGURE 1. — DROPOUT VOLTAGE vs. TEMPERATURE

Junction Temperature - (°C)

Frequency Drift - (%)

-10

-75 -50-25 0255075100125

-8

-6

-4

-2

= 15V

Duty Cycle = 50%

Junction Temperature - (°C)

Minimum Operating Voltage - (V)

8.0

-75 -50-25 0 255075100125

8.4

8.8

9.2

9.6

10.0

SG1842

SG1843

Junction Temperature - (°C)

Current Sense Delay - (nS)

120

-75 -50-25 0 255075100125

140

160

180

200

220

PIN3

= 1.1V

Junction Temperature - (°C)

Output Duty Cycle - (%)

-75 -50-25 0 255075100125

50kHz

100kHz

200kHz

50kHz

200kHz

100kHz

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PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

CHARACTERISTIC CURVES

FIGURE 6. — REFERENCE VOLTAGE vs. TEMPERATURE

FIGURE 7. — START-UP VOLTAGE THRESHOLD vs.

TEMPERATURE

FIGURE 8. — START-UP VOLTAGE THRESHOLD vs.

TEMPERATURE

FIGURE 5. — START-UP CURRENT vs. TEMPERATURE

Junction Temperature - (°C)

Reference Voltage - (V)

4.98

-75 -50-25 0255075100125

= 15V

4.99

5.00

5.01

5.02

Junction Temperature - (°C)

Start-Up Current - (mA)

0.2

-75 -50-25 0 255075100125

0.3

0.4

0.5

0.6

0.7

SG1842

SG1843

Junction Temperature - (°C)

Reference Voltage - (V)

8.18-75 -50-25 0 255075100125

SG1843

8.22

8.26

8.30

8.32

8.20

8.24

8.28

Junction Temperature - (°C)

Start Up Voltage - (V)

16.00

-75 -50-25 0 255075100125

SG1842

16.02

16.04

16.06

16.08

15.98

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ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

CHARACTERISTIC CURVES

FIGURE 10. — OUTPUT SATURATION VOLTAGE vs.

OUTPUT CURRENT & TEMPERATURE

FIGURE 11. — CURRENT SENSE THRESHOLD vs.

ERROR AMPLIFIER OUTPUT

FIGURE 12. — OUTPUT SATURATION VOLTAGE vs.

OUTPUT CURRENT & TEMPERATURE

FIGURE 9. — OSCILLATOR DISCHARGE CURRENT vs.

TEMPERATURE

Output Current - (mA)

Saturation Voltage - (V)

0.5

100 200 300 400 500

1.0

1.5

2.0

2.5

-55°C

+25°C

+125°C

= 15V

Duty Cycle < 5%

Junction Temperature - (°C)

Oscillator Discharge Current - (mA)

7.4

-75 -50-25 0255075100125

7.6

7.8

8.0

8.2

7.2

Error Amp Output Voltage - (V)

Current Sense Threshold - (V)

0.2

1.0 2.0 3.0 4.0 5.0

0.4

0.6

0.8

1.0

0.1

0.3

0.5

0.7

0.9

125°C

25°C

-55°C

Output Current - (mA)

Saturation Voltage - (V)

1.0

100 200 300 400 500

2.0

3.0

4.0

= 15V

Duty Cycle < 5%

-55°C

+25°C

+125°C

+25°C

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PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

APPLICATION INFORMATION

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.

FIGURE 13 — OSCILLATOR TIMING CIRCUIT

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

Calculate: RT = 267 (Ω)

where .3 < Dm < .95

CT = (µF)

For Duty-Cycles above 95% use:

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?

Given: f = 50kHz

Dm = 0.45

Calculate: RT = 267 = 674Ω

CT = = .025µF

(1.76)1/.045 -1

(1.76).55/.45 - 1













1.86 * 0.45

50000 * 674

(1.76)1/Dm -1

(1.76)(1-Dm)/Dm - 1













1.86 * Dm

f * RT

REF

GND

.001

CT Value - (µF)

1000

f - (kHz)

.002 .02

100

.005 .01 .05 0.1

= 680

= 2k

= 5k

= 10k

= 20k

= 30k

= 50k

= 70k

= 100k

FIGURE 14 — OSCILLATOR FREQUENCY vs. RT FOR VARIOUS CT

F ≈where RT ≥ 5kΩ

1.86

RTCT

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ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS

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.

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.

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

FIGURE 15. — CURRENT-SENSE SPIKE SUPPRESSION 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 induc-

tance 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.)

The RC low pass filter will eliminate the leading edge current spike

caused by parasitics of Power MOSFET.

7 (12)

7 (11)

6 (10)

5 (8)

3 (5)

PK(MAX)

= 1.0V

SG1842/43

7 (12)

7 (11)

6 (10)

5 (8)

SG1842/43

3 (5)

SG1842/43

3 (5)

5 (8)

6 (10)

7 (11)



|| R

_

7 (12)

7 (11)

6 (10)

5 (8)

3 (5)

SG1842/43

Isolation

Boundary

Waveforms

50% DC

25% DC

IPK = V (PIN 1) - 1.4

3RS













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PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

FIGURE 20. — EXTERNAL DUTY CYCLE CLAMP AND

MULTI-UNIT SYNCHRONIZATION

FIGURE 19. — ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL

WITH SOFTSTART

Precision duty cycle limiting as well as synchronizing several 1842/

1843's is possible with the above circuitry.

Softstart and adjustable peak current can be done with the external

circuitry shown above.

tSOFTSTART = -ln 1 - C

where; VEAO ≡ voltage at the Error Amp Output under

minimum line and maximum load conditions.

IPK = Where: VCS = 1.67 and VC.S.MAX = 1V (Typ.)

7 (12)

6 (10)

7 (11)

5 (8)

3 (5)

SG1842/43

5 (9)

8 (14)

4 (7)

2 (3)

1 (1)

MPSA63

1N4148

555

TIMER 4 (7)

5 (9)

8 (14)

SG1842/43

To other

SGX842/43

















































FIGURE 22. — ERROR AMPLIFIER CONNECTIONFIGURE 21. — OSCILLATOR CONNECTION

8 (14)

4 (7)

2.8V

1.1V

SG1842/43

Discharge

Current I

= 8.2mA

1 (1)

2 (3)

 10K

2.5V

SG1842/43

0.5mA

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.

Error amplifier is capable of sourcing and sinking current up to 0.5mA.

R1 R2

R1+R2

VEAO - 1.3

5 R1

R1+R2

R1+R2f = (RA + 2RB)C

1.44

f = RA + 2RB

VCS

URRENT

-M

ODE

PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

FIGURE 23. — SLOPE COMPENSATION

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.

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.

OSCILLATOR

REF

GOOD LOGIC

R 5V

REF

INTERNAL

BIAS

8(14)

4(7)

2(3)

1(1)

From V

SLOPE

2N222A

UVLO

2.5V

ERROR

AMP

C.S.

COMP

PWM

LATCH

5(9)

3(5)

5(8)

6(10)

7(11)

7(12)

SG1842/43

FIGURE 24. — OPEN LOOP LABORATORY FIXTURE

COMP

SENSE

REF

OUTPUT

GROUND

0.1µF 0.1µF

SG1842/43

2N2222

100K

4.7K

4.7K 5K

SENSE

ADJUST

ERROR AMP

ADJUST

GROUND

OUTPUT

REF

URRENT

-M

ODE

PWM C

ONTROLLER

SG1842/SG1843 Series

PRODUCT DATABOOK 1996/1997

Rev. 1.6a 10/04

PRODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

FIGURE 25. — OFF-LINE FLYBACK REGULATOR

150k

100pF

COMP

REF

4700µF

10V 5V

2-5A

ISOLATION

BOUNDARY

0.01pF

400V

1N3613

820pF

2.5k

1N3613

UFN432

27

0.01µF

10µF

20V

1N3613

1k

470pF 0.85

USD 735

220µF

250V

4.7 1W

673-3

INPUT

OUT

CUR

SEN

GND

SG1842

20k

3.6k

10k

.0047µF0.01µF

16V

56k

20k

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

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.