Features: · Current sensing with 100mV threshold
· Common-mode input at ground to 40V
· Complementary outputs
· Automatic reset from PWM clock
· 180ns delay
· Interface direct to SG1524, SG1525A, SG1527AApplicationHIGH 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.
Pinout
SpecificationsInput Supply Voltage, VS .....................................................25V
HI CM Input Voltage ............................................................40V
LO Output "off" Voltage .......................................................40V
LO Output "on" current .....................................................25mA
Operating Junction Temperature
Hermetic (Y Package) ..................................................150°C
Plastic (N Package) ......................................................150°C
Storage Temperature Range ............................-65°C to 150°C
DescriptionThis SG1549 is an analog latch device with digital reset. SG1549 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 SG1549, SG1524, SG1525A and SG1527A.
The input threshold of SG1549 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, the SG1549 is ideal for fast reaction sensing to provide overall current limiting, short circuit protection, or transformer saturation control.
SG1549 Data Sheet
