Datasheet SG1540Y-883B, SG2540DW, SG2540M, SG2540Y, SG3540DW Datasheet (Microsemi Corporation)

SG1540/SG2540/SG3540

OFF-LINE START-UP CONTROLLER

DESCRIPTION

The SG1540 is an integrated circuit designed to efficiently provide
start-up power from a high-voltage DC bus to a PWM control circuit
in a switching power supply. When used on the primary side, it
reduces start-up current to less than 1mA and allows any standard
PWM control circuit to be used as a primary-side controller. When
used to power a controller on the secondary side, it efficiently
eliminates the need for a heavy 50/60Hz line transformer with its
associated low frequency magnetic fields.

The circuit consists of three sections: a micropower bandgap
comparator/power switch referenced to 2.5 volts which isolates the
start-up capacitor from its load; a high frequency square-wave
oscillator with 200mA totem-pole output for driving an isolation
transformer; and a second bandgap comparator with latching
crowbar to protect against overvoltage faults while starting or
running.

The SG1540 is specified for operation over the full military ambient
temperature range of -55°C to 125°C. The SG2540 is character­ized for the industrial range of -25°C to 85°C, and the SG3540 is
designed for the commercial range of 0°C to 70°C.

BLOCK DIAGRAM

FEATURES

••

• Useable with primary and secondary side PWM

••

controllers

••

• Micropower comparator / switch

••

- Internal 2.5V bandgap reference

- 50mA power switch

••

• Squarewave oscillator

••

- 500Hz to 200KHz operation

- 200mA totem pole outputs

••

• Eliminates bulky, expensive 50/60 Hz transformer

••

••

• Minimizes high voltage bleeder current

••

••

• Programmable start-up voltage and hysteresis

••

••

• Internal and programmable overvoltage crowbar

••

latch

••

• Available in 8 pin DIP, 10 pin flat pack, and 16 pin

••

widebody SOIC

HIGH RELIABILITY FEATURES - SG1540

♦♦

♦ Available to MIL-STD - 883

♦♦
♦♦

♦ LMI level "S" processing available

♦♦

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ABSOLUTE MAXIMUM RATINGS (Note 1)

Supply Voltage (+V
DC Output Current, Continuous (V

AC Output Current, Continuous ..................................... 200mA

Analog Inputs (Start and Overvoltage) .................-0.3V to 6.0V

Analog Input Currents (V>8V).......................................... 10mA

Overvoltage Crowbar Current, Continuous ..................... 50mA

Note 1. Values beyond which damage may occur.

)........................................................ +37V

IN

)........................... 100mA

OUT

THERMAL DATA

Y Package:

Thermal Resistance­Thermal Resistance-

M Package:

Thermal Resistance­Thermal Resistance-

DW Package:

Thermal Resistance­Thermal Resistance-

Junction to Case, θ
Junction to Ambient, θ

Junction to Case, θ
Junction to Ambient, θ

Junction to Case, θ
Junction to Ambient, θ

JC

JC

JC

.................. 50°C/W

............ 130°C/W

JA

.................. 60°C/W

............. 95°C/W

JA

.................. 40°C/W

............. 95°C/W

JA

RECOMMENDED OPERATING CONDITIONS (Note 2)

Supply Voltage Range ............................................... 7V to 35V

DC Output Current, Continuous................................ 0 to 50mA

AC Output Current, Continuous ............................. 0 to 100 mA

Oscillator Frequency Range ........................... 1KHz to 400KHz

Timing Resistor Range ...................................... 2KΩ to 150KΩ

Note 2. Range over which the device is functional.

SG1540/SG2540/SG3540

Overvoltage Crowbar Energy (½CV²)................................. 8mJ

Operating Junction Temperature

Hermetic (Y Package) ................................................ 150°C

Plastic (M, DW Packages) .......................................... 150°C

Storage Temperature Range ............................ -65°C to 150°C

Lead Temperature (Soldering, 10 Seconds) .................. 300°C

Note A. Junction Temperature Calculation: TJ = TA + (PD x θJA).
Note B. The above numbers for θ

thermal resistance of the package in a standard mount­ing configuration. The θ
guidelines for the thermal performance of the device/pc­board system. All of the above assume no ambient
airflow.

Timing Capacitor Range ........................................ 1nF to 20µF

Operating Ambient Temperature Range

SG1540 ...........................................................-55°C to 125°C

SG2540 .............................................................-25°C to 85°C

SG3540 ................................................................ 0°C to 70°C

are maximums for the limiting

JC

numbers are meant to be

JA

ELECTRICAL CHARACTERISTICS

(Unless otherwise specified, these specifications apply over the operating ambient temperatures for SG1540 with -55°C ≤ TA ≤ 125°C, SG2540 with

-25°C ≤ TA ≤ 85°C, SG3540 with 0°C ≤ TA ≤ 70°C, and +VIN = 15V. A 0.1µF high frequency bypass capacitor is recommended on VIN. Low duty cycle
testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)

SG1540/2540/3540

Min.

Typ. Max.

0.2

0.4

0.3

0.6

3

6

2.37

2.50

2.63

6

12.5

12.0
50

0.1

0.1

13.5

13.0
100 225

1

7

8

0.2

Units

mA
mA
mA

V

µA

V
V

V
V

mA

Start-up Section

Start Current I

CC

Operating Current
Start Threshold

Start Bias Current
Start Clamp Voltage
Hysteresis ON Voltage

DC Output Section

Voltage

V

OUT

Short Circuit Current

V

= 0 to 2.37V

START

V

TIMING

F

= 50KHz, V

OSC

= 0 to 5V

V

PIN 1

I

= 1mA

PIN 1

= 100µA

I

PIN 4

I

SOURCE

I

SOURCE

V

= 0V

OUT

= +VIN; V

= 10mA
= 50mA

Test ConditionsParameter

Open

OUT

and AC

OUT

OUT

Open

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ELECTRICAL CHARACTERISTICS (continued)

SG1540/SG2540/SG3540

Parameter Units

Test Conditions

Oscillator Section (Note 3)

Initial Accuracy
Voltage Stability
Temperature Stability

(Note 4)

Oscillator Minimum Frequency
Oscillator Maximum Frequency

TJ = 25°C
+V

= 12 to 18V

IN

= 17.8K, CT = .068µF

R

T

R

= 1.5K, CT = 470pF

T

AC Output Section

I

HIGH Output Voltage
LOW Output Voltage
Squarewave Duty Cycle

AC Output Risetime
AC Output Falltime

SOURCE

I

SOURCE

= 20mA

I

SINK

I

= 100mA

SINK

= 1000pF

C

L

C

= 1000pF

L

= 20mA
= 100mA

Overvoltage Crowbar Section

Overvoltage Threshold
Overvoltage Bias Current
Overvoltage Clamp Voltage
+V

Overvoltage Threshold

IN

SCR ON Voltage
SCR Holding Current

Note 3. F
Note 4. These parameters, although guaranteed, are not tested in production.

= 50KHz, RT = 3.48K CT = 4.7nF unless otherwise specified.

OSC

V

= 0 to 2.37V

O.V.

= 1mA

I

O.V.

= 35mA

I

VIN

V

= 0

O.V.

SG1540/2540/3540

Min. Typ. Max.

46

50

54

5

12

2

5
1

400

13.5

12.5

13.0

12.0

0.3

0.2

2.0

1.2

50

45

2.37
6

37

0.15

2.50

0.35

0.3

0.1

0.1
42

55

0.6

0.2

2.63
1

7

8

44

9

12

0.55

KHz

%

%
KHz
KHz

V
V
V
V

%

µS
µS

V

µA

V
V
V

mA

CHARACTERISTIC CURVES

FIGURE 1 - SATURATION VOLTAGE (DC OUT PIN) VS. OUTPUT CURRENT

FIGURE 2 - OSCILLATOR FREQUENCY VS. RT AND C

T

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SG1540/SG2540/SG3540

APPLICATION INFORMATION

FIGURE 3 - EFFICIENT PRIMARY SIDE START-UP

PRIMARY SIDE START-UP

When the design goal is efficient start-up for a control PWM referenced to the primary side of the power transformer, the configuration
in Figure 3 is recommended. An energy storage capacitor C
The value of R
C

ramps up from zero, the only load current is the standby current of the SG1540 and that of the divider network R1-R3. (Connecting

START

the TIMING pin to +V
bias current at the START pin is 1µA maximum, a divider current of 100µA is adequate).

is chosen to provide a constant 1mA charging current, allowing the use of a ½ watt resistor. As the voltage on

START

disables the internal power oscillator and forces the circuitry into a micropower standby model. Since the input

IN

is trickle-charged from the 300-400 Volt DC bus by resistor R

START

START

.

When the voltage at the START pin reaches +2.5 Volts, the hysteresis transistor turns off, overdriving the START pin. The V
is switched to the HIGH state, providing power to the PWM control circuit. As energy flows out of the START capacitor, its voltage
decays; but it remains connected to the PWM circuit until the dropout voltage is reached (V
on the power transformer and rectifier diode D5 prevent this from happening. As the PWM control circuit becomes active, the power

START

- V

HYSTERESIS

). The bootstrap winding

OUT

pin

transistor begins to switch, providing operating current to the PWM circuit through the SG1540.

RESISTOR CALCULATIONS

Given that V
are calculated as follows:

1. For simplification, let X =

START

and V

have been chosen, and that the divider current at start-up is 100µA, then the values for R1 through R3

DROPOUT

V

- 2.5

and Y =

START

V

DROPOUT

2.5

2.5

-2.5

2. Then,R1 = 2.5 x 10
R2 = R1/Y [2]

and R3 = [3]

4

* X [1]

R1 * R2

X * R2 - R1

DESIGN EXAMPLE

Suppose we have a power MOSFET device, and so want to start at +18 volts and drop out at +12 volts.

Then X = 6.20

and Y = 3.80

4

Therefore R1 = 2.5 x 10

R2 = 1.5 x 10
R3 = = 63.7K (Choose 62K)

6.2 * 3.9 x 104 - 1.5 x 10

* 6.2 = 155K (Choose 150K)

5

/3.8 = 39.5K (Choose 39K)

1.5 x 105 * 3.9 x 10

4

5

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APPLICATIONS INFORMATION (continued)

The voltage waveform at +VIN is shown in Figure 4 with these resistor values and with C
before the +15 volt bootstrap winding becomes active.

SG1540/SG2540/SG3540

= 3µF. Notice that two tries are required

START

FIGURE 4 - STARTUP VOLTAGE WAVEFORM

FIGURE 5 - SECONDARY-SIDE START-UP WITHOUT A LINE TRANSFORMER

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CONNECTION DIAGRAMS & ORDERING INFORMATION (See Notes Below)

SG1540/SG2540/SG3540

8-PIN CERAMIC DIP
Y - PACKAGE

8-PIN PLASTIC DIP
M - PACKAGE

16-PIN WIDE BODY
PLASTIC S.O.I.C.
DW - PACKAGE

Part No.Package

Ambient

Temperature Range

SG1540Y/883B -55°C to 125°C
SG1540Y -55°C to 125°C
SG2540Y -25°C to 85°C
SG3540Y 0°C to 70°C

SG2540M -25°C to 85°C
SG3540M 0°C to 70°C

SG2540DW -25°C to 85°C
SG3540DW 0°C to 70°C

Connection Diagram

START

OVER VOLTAGE

HYSTERESIS

TIMING

START

N.C.

OVER VOLTAGE

N.C.

HYSTERESIS

N.C.

TIMING

N.C.

8

1
2
3
4

1
2
3
4
5
6
7
8

7
6
5

16
15
14
13
12
11
10

DC OUT
+V
AC OUT
GROUND

9

IN

DC OUT
N.C.
+V
N.C.
AC OUT
N.C.
GROUND
N.C.

IN

Notes: 1. Contact factory for JAN and DESC part availability.

2. All parts are viewed from the top.

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