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SG1549/SG2549/SG3549
CURRENT SENSE LATCH
DESCRIPTION
This monolithic integrated circuit is an analog latch device with digital reset. It was specifically designed to provide pulse-by-pulse current limiting for switch-mode power supply systems, but many other application are also feasible. Its function is to provide a latching switch action upon sensing an input threshold voltage, with reset accomplished by an external clock signal. This device can be interfaced directly with many kinds of pulse width modulating control IC's, including the SG1524, SG1525A and SG1527A. The input threshold for the latch circuit is 100mV, which can be referenced either to ground or to a wide-ranging positive voltage. There are high and low-going output signals available, and both the supply voltage and clock signal can be taken directly from an associated PWM control chip. With delays in the range of 200 nanoseconds, this latch circuit is ideal for fast reaction sensing to provide overall current limiting, short circuit protection, or transformer saturation control.
FEATURES
* Current sensing with 100mV threshold * Common-mode input at ground or to 40V * Complementary outputs * Automatic reset from PWM clock * 180ns delay * Interface direct to SG1524, SG1525A, SG1527A
HIGH RELIABILITY FEATURES - SG1549
Available to MIL-STD-883 LMI level "S" processing available Radiation data available
BLOCK DIAGRAM
SCHEMATIC
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.
SG1549/SG2549/SG3549
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage, VS ..................................................... 25V HI CM Input Voltage ............................................................ 40V LO Output "off" Voltage ....................................................... 40V LO Output "on" current ..................................................... 25mA
Note 1. Values beyond which damage may occur.
Operating Junction Temperature Hermetic (Y Package) .................................................. 150C Plastic (N Package) ...................................................... 150C Storage Temperature Range ............................ -65C to 150C
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
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)
Input Supply Voltage, VS .................................................... 5.0V HI CM Input Voltage .................................................. 2V to 40V LO Output "off" Voltage ............................................. 5V to 40V LO Output "on" Current ............................................. 0 to 10mA Reset LO Voltage ..................................................... 0V to 0.8V
Note 2. Range over which the device is functional.
Reset HI Voltage .................................................... 2.5V to 5.0V Operating Ambient Temperature Range SG1549Y ....................................................... -55C to 125C SG2549Y or M ................................................. -25C to 85C SG3549Y or M .................................................... 0C to 70C
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for SG1549 with -55C TA 125C, SG2549 with -25C TA 85C, SG3549 with 0C TA 70C, and VS = 5V. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)
Parameter Supply Section Supply Current LO CM Input Section (Note 3) Threshold Voltage Input Impedance HI CM Input Section (Note 3) Threshold Voltage VPIN 8 = 5V VPIN 8 = 20V
Test Conditions
SG1549/2549 SG3549 Units Min. Typ. Max. Min. Typ. Max. 2 10 80 70 400 300 80 80 70 70 100 100 500 500 100 100 100 100 200 2.0 20 3 15 120 130 600 700 120 120 130 130 300 2.5 40 80 70 400 300 80 80 70 70 2 10 100 100 500 500 100 100 100 100 200 2.0 20 5 15 120 130 600 700 120 120 130 130 300 2.5 40 mA mA mV mV mV mV mV mV A V A
Pin 1 & 2 shorted, TA = 25C pin 1 & 2 shorted VPIN 3 = 50mV, TA = 25C VPIN 3 = 50mV VCM = 2V, Pin 3 open, TA = 25C VCM = 40V, Pin 3 open, T A = 25C VCM = 2V, Pin 3 open VCM = 40V, Pin 3 open VPIN 1 = VPIN 2 = 40V
Input Current Clock Reset Section Min. Trigger Voltage Input Current
VPIN 7 = 4V
Note 3. Input threshold voltages and supply current are directly proportional to supply voltage, VS .
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.
SG1549/SG2549/SG3549
ELECTRICAL CHARACTERISTICS
(VS = 5V, and over recomended operating temperature, unless otherwise specified.)
Parameter HI Output Section Off Voltage On Voltage LO Output Off Leakage On Voltage
Test Conditions
SG1549/2549 SG3549 Units Min. Typ. Max. Min. Typ. Max. 0 3.2 .01 .3 0.1 2.8 1.0 0.5 0 3.2 .01 .3 0.1 V V A V
IL = 1mA VPIN 5 = 40V IL = 5mA
(Note 4)
2.8
1.0 0.5
TYPICAL SWITCHING CHARACTERISTICS
(VS = 5V, TA = 25C)
Parameter Reset Minimum Pulse Width (TW1) Delay from Reset to LO Output (TD(OFF)) LO Input Minimum Pulse Width (TW2) Delay from LO Input to LO Output (TD(ON)) Delay from HI Input to LO Output (TD(ON)) Delay from HI Output to LO Output
Test Conditions Amplitude = 3.0V RL = 470 to V S LO CM Amplitude = 200mV LO CM Amplitude = 200mV, RL = 470 to VS Amplitude = 200mV, VCM = 5V LO CM Input = 200mV
SG1549 Series Units Min. Typ. Max. 150 300 ns ns 300 600 50 300 ns 180 360 ns 300 900 ns 30 60 ns
Note 4: These parameters, although guaranteed, are not tested in production.
DYNAMIC TEST CIRCUIT
SWITCHING WAVEFORMS
APPLICATION NOTES
HIGH LINE SENSING - The SG1549 will provide current sensing in the positive supply line in the typical SG1524 single-ended switching regulator application shown in Figure 1. The HI CM sense circuitry can be used with input voltages between 2 and 40 volts. A value for RSC is determined by dividing the 100mV input threshold by the peak current desired. High-frequency noise, or switching transients, can usually be eliminated by a small capacitor between pins 3 and 4. Current control may be accomplished by either the HI OUTPUT pin connected to the SG1524's Shutdown pin, or the LO OUTPUT pin connected directly to the Compensation Terminal. In either case, activation of the current sense latch will tend to discharge the compensation capacitor, CC, which may cause slow recovery from pulse limiting. If this feature is desired, the LO OUTPUT pin may be used to discharge a soft-start network instead of coupling directly to the SG1524. If it is not desired, the use of a small value of CC, and perhaps a diode across RC, will enhance recovery.
FIGURE 1 -- HIGH LINE SENSING WITH THE SG1549 IN CONJUNCTION WITH AN SG1524 PWM CONTROL IC
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.
SG1549/SG2549/SG3549
APPLICATION NOTES
(continued)
Another method of introducing the current shutdown signal is shown in Figure 2 where the SG1524 is used to activate a constant drive current to the high-current switch, in this case an SM600. The 2N2222 forms a constant current generator when driven from the SG1524's 5.0 volt reference through a 1K resistor. This transistor is then switched off by the LO OUTPUT transistor in the SG1549, achieving the fastest response to the output of the regulator. LOW LINE SENSING - In many types of feed-forward or push-pull converters, current protection may be provided by sensing in an emitter resistor referenced to ground on the primary side of an output transformer. The fast-reacting SG1549 can easily sense secondary overload as reflected back to the primary and, additionally, provide protection from unbalanced transformer saturation. When using the LO CM inputs, the HI CM inputs should be shorted together. While the LO CM inputs may be connected directly across a sense resistor, RSC , a small low-pass filter as shown in Figure 3 is often required to eliminate high frequency transients. It must be remembered that the 500 input impedance at the LO CM terminals will cause the use of R1 to increase the effective threshold; however, this also offers the possibility of an easily adjustable threshold by incorporating a potentiometer at the input. Coupling the output signal from the SG1549 to the control chip may be done in several ways including the use of either the Compensation or Shutdown pins on the SG1524 as described earlier. Another convenient way to tie the output of the SG1549 into the PWM control in higher power applications is by using the SG1627 Dual Interface Driver and connecting the LO OUTPUT terminal of the Sg1549 directly to the two Non-Inverting inputs of the SG1627 as shown in Figure 4. And finally, keep in mind that the LO OUTPUT terminal of the SG1549 will easily drive most high-speed optical couplers should some type of isolation between current sense and shutdown control be required.
FIGURE 2 -- CURRENT CONTROL FOR A BUCK REGULATOR WITH CONSTANT DRIVE CURRENT
FIGURE 3 -- A PUSH-PULL CONVERTER WITH LOW-LINE EMITTER CURRENT SENSING
FIGURE 4 -- POWER BOOST AND CURRENT CONTROL WITH THE SG1627
CONNECTION DIAGRAMS & ORDERING INFORMATION
Package
8-PIN CERAMIC DIP Y - PACKAGE
(See Notes Below)
Part No. SG1549Y/883B SG1549Y/DESC SG1549Y SG2549Y SG3549Y SG2549M SG3549M
Ambient Temperature Range -55C to 125C -55C to 125C -55C to 125C -25C to 85C 0C to 70C -25C to 85C 0C to 70C
Connection Diagram
+ HI CM INPUT -- HI CM INPUT + LO CM INPUT -- LO CM INPUT
1 2 3 4
8 7 6 5
+VS CLOCK RESET HI OUTPUT LO OUTPUT
8-PIN PLASTIC DIP M - PACKAGE
Note 1. Contact factory for JAN and DESC product availability. 4/90 Rev 1.1 2/94
Copyright (c) 1994
2. All parts are viewed from the top.
11861 Western Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
LINFINITY
Microelectronics Inc.
4

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