Rev 1.1a 03/17/2005

Microsemi Inc.

Copyright

© 1994

11861 Western Avenue

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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 accom-

plished 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

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♦ Available to MIL-STD-883

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♦ LMI level "S" processing available

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♦ Radiation data available

BLOCK DIAGRAM

SCHEMATIC