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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 -55C to 125C. The SG2540 is characterized for the industrial range of -25C to 85C, and the SG3540 is designed for the commercial range of 0C to 70C.
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
BLOCK DIAGRAM
4/90 Rev 1.1 2/94
Copyright (c) 1994
1
11861 Western Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
LINFINITY
Microelectronics Inc.
SG1540/SG2540/SG3540
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (+VIN ) ........................................................ +37V DC Output Current, Continuous (VOUT) ........................... 100mA 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.
Overvoltage Crowbar Energy (1/2CV) ................................. 8mJ Operating Junction Temperature Hermetic (Y Package) ................................................ 150C Plastic (M, DW Packages) .......................................... 150C Storage Temperature Range ............................ -65C to 150C Lead Temperature (Soldering, 10 Seconds) .................. 300C
THERMAL DATA
Y Package: Thermal Resistance-Junction to Case, JC .................. 50C/W Thermal Resistance-Junction to Ambient, JA ............ 130C/W M Package: Thermal Resistance-Junction to Case, JC .................. 60C/W Thermal Resistance-Junction to Ambient, JA ............. 95C/W DW Package: Thermal Resistance-Junction to Case, JC .................. 40C/W Thermal Resistance-Junction to Ambient, JA ............. 95C/W
Note A. Junction Temperature Calculation: TJ = TA + (PD x JA). Note B. The above numbers for JC are maximums for the limiting
thermal resistance of the package in a standard mounting configuration. The JA numbers are meant to be guidelines for the thermal performance of the device/pcboard system. All of the above assume no ambient airflow.
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 ...................................... 2K to 150K
Note 2. Range over which the device is functional.
Timing Capacitor Range ........................................ 1nF to 20F Operating Ambient Temperature Range SG1540 ........................................................... -55C to 125C SG2540 ............................................................. -25C to 85C SG3540 ................................................................ 0C to 70C
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for SG1540 with -55C TA 125C, SG2540 with -25C TA 85C, SG3540 with 0C TA 70C, and +VIN = 15V. A 0.1F high frequency bypass capacitor is recommended on V IN. Low duty cycle testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)
Parameter Start-up Section Start Current ICC Operating Current Start Threshold Start Bias Current Start Clamp Voltage Hysteresis ON Voltage DC Output Section VOUT Voltage Short Circuit Current
Test Conditions VSTART = 0 to 2.37V VTIMING = +VIN ; VOUT Open FOSC = 50KHz, VOUT and AC OUT Open VPIN 1 = 0 to 5V IPIN 1 = 1mA IPIN 4 = 100A ISOURCE = 10mA ISOURCE = 50mA VOUT = 0V
SG1540/2540/3540 Units Min. Typ. Max. 0.2 0.3 3 2.37 2.50 0.1 6 7 0.1 12.5 12.0 50 13.5 13.0 100 0.4 0.6 6 2.63 1 8 0.2 mA mA mA V A V V V V mA
225
4/90 Rev 1.1 2/94
Copyright (c) 1994
2
11861 Western Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
LINFINITY
Microelectronics Inc.
SG1540/SG2540/SG3540
ELECTRICAL CHARACTERISTICS (continued)
Parameter Oscillator Section (Note 3) Initial Accuracy Voltage Stability Temperature Stability (Note 4) Oscillator Minimum Frequency Oscillator Maximum Frequency AC Output Section HIGH Output Voltage LOW Output Voltage Squarewave Duty Cycle AC Output Risetime AC Output Falltime Overvoltage Crowbar Section Overvoltage Threshold Overvoltage Bias Current Overvoltage Clamp Voltage +VIN Overvoltage Threshold SCR ON Voltage SCR Holding Current TJ = 25C +VIN = 12 to 18V RT = 17.8K, CT = .068F RT = 1.5K, CT = 470pF ISOURCE = 20mA ISOURCE = 100mA ISINK = 20mA ISINK = 100mA CL = 1000pF CL = 1000pF 2.37 VO.V. = 0 to 2.37V IO.V. = 1mA IVIN = 35mA VO.V. = 0 6 37 0.15 Test Conditions SG1540/2540/3540 Units Min. Typ. Max. 46 50 5 2 54 12 5 1 KHz % % KHz KHz V V V V % S S V A V V V mA
400 12.5 12.0 13.5 13.0 0.2 1.2 50 0.3 0.1 2.50 0.1 7 42 9 0.35
45
0.3 2.0 55 0.6 0.2 2.63 1 8 44 12 0.55
Note 3. FOSC = 50KHz, RT = 3.48K C T = 4.7nF unless otherwise specified. Note 4. These parameters, although guaranteed, are not tested in production.
CHARACTERISTIC CURVES
FIGURE 1 - SATURATION VOLTAGE (DC OUT PIN) VS. OUTPUT CURRENT
FIGURE 2 - OSCILLATOR FREQUENCY VS. RT AND CT
4/90 Rev 1.1 2/94
Copyright (c) 1994
3
11861 Western Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
LINFINITY
Microelectronics Inc.
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 CSTART is trickle-charged from the 300-400 Volt DC bus by resistor RSTART. The value of RSTART is chosen to provide a constant 1mA charging current, allowing the use of a 1/2 watt resistor. As the voltage on CSTART ramps up from zero, the only load current is the standby current of the SG1540 and that of the divider network R1-R3. (Connecting the TIMING pin to +VIN disables the internal power oscillator and forces the circuitry into a micropower standby model. Since the input bias current at the START pin is 1A maximum, a divider current of 100A is adequate). When the voltage at the START pin reaches +2.5 Volts, the hysteresis transistor turns off, overdriving the START pin. The VOUT pin 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 (VSTART - VHYSTERESIS). The bootstrap winding on the power transformer and rectifier diode D5 prevent this from happening. As the PWM control circuit becomes active, the power transistor begins to switch, providing operating current to the PWM circuit through the SG1540. RESISTOR CALCULATIONS Given that VSTART and VDROPOUT have been chosen, and that the divider current at start-up is 100A, then the values for R1 through R3 are calculated as follows: 1. For simplification, let X = VSTART - 2.5 2.5 VDROPOUT -2.5 2.5 2. Then,R1 = 2.5 x 104 * X R2 = R1/Y and R3 = R1 * R2 X * R2 - R1 [1] [2] [3]
and Y =
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 R1 = 2.5 x 104 * 6.2 = 155K R2 = 1.5 x 105/3.8 = 39.5K R3 = 1.5 x 105 * 3.9 x 104 = 63.7K 6.2 * 3.9 x 104 - 1.5 x 105 (Choose 150K) (Choose 39K) (Choose 62K)
Therefore
4/90 Rev 1.1 2/94
Copyright (c) 1994
4
11861 Western Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
LINFINITY
Microelectronics Inc.
SG1540/SG2540/SG3540
APPLICATIONS INFORMATION (continued)
The voltage waveform at +VIN is shown in Figure 4 with these resistor values and with CSTART = 3F. Notice that two tries are required before the +15 volt bootstrap winding becomes active.
FIGURE 4 - STARTUP VOLTAGE WAVEFORM
FIGURE 5 - SECONDARY-SIDE START-UP WITHOUT A LINE TRANSFORMER
4/90 Rev 1.1 2/94
Copyright (c) 1994
5
11861 Western Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
LINFINITY
Microelectronics Inc.
SG1540/SG2540/SG3540
CONNECTION DIAGRAMS & ORDERING INFORMATION (See Notes Below)
Package
8-PIN CERAMIC DIP Y - PACKAGE
Part No. SG1540Y/883B SG1540Y SG2540Y SG3540Y SG2540M SG3540M SG2540DW SG3540DW
Ambient Temperature Range -55C to 125C -55C to 125C -25C to 85C 0C to 70C -25C to 85C 0C to 70C -25C to 85C 0C to 70C
Connection Diagram
START OVER VOLTAGE HYSTERESIS TIMING
1 2 3 4
8 7 6 5
DC OUT +VIN AC OUT GROUND
8-PIN PLASTIC DIP M - PACKAGE 16-PIN WIDE BODY PLASTIC S.O.I.C. DW - PACKAGE
START N.C. OVER VOLTAGE N.C. HYSTERESIS N.C. TIMING N.C.
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
DC OUT N.C. +VIN N.C. AC OUT N.C. GROUND N.C.
Notes:
1. Contact factory for JAN and DESC part availability. 2. All parts are viewed from the top.
11861 Western Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
4/90 Rev 1.1 2/94
Copyright (c) 1994
LINFINITY
Microelectronics Inc.
6

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