SG3525A Pulse Width Modulator Control Circuit

The SG1525A series of pulse width modulator integrated circuits are designed to offer improved performance and lower external parts count when used to implement all types of switching power supplies. The on-chip +5.1 V reference is trimmed to ±1% initial accuracy and the input common-mode range of the error amplifier includes the reference voltage, eliminating external potentiometers and divider resistors. A Sync input to the oscillator allows multiple units to be slaved together, or a single unit to be synchronized to an external system clock. A single resistor between the CT pin and the Discharge pin provides a wide range of deadtime adjustment. These devices also feature built-in soft-start circuitry with only a timing capacitor required externally. A Shutdown pin controls both the soft-start circuitry and the output stages, providing instantaneous turn-off with soft-start recycle for slow turn-on. These functions are also controlled by an undervoltage lockout which keeps the outputs off and the soft-start capacitor discharged for input voltages less than that required for normal operation. Another unique feature of these PWM circuits is a latch following the comparator. Once a PWM pulse has been terminated for any reason, the outputs remain off for the duration of the period. The latch is reset with each clock pulse. The output stages are totempole designs capable of sourcing or sinking in excess of 200mA.
The SG1525A output stage features NOR logic, giving a LOW output for an OFF state. The SG1527A utilizes OR logic, which results in a HIGH output level when OFF.

Features
■ 8V to 35V Operation
■ 5.1V Reference Trimmed to 1%
■ 100Hz to 500kHz Oscillator Range
■ Separate Oscillator Sync Terminal
■ Adjustable Deadtime Control
■ Internal Soft-start
■ Input Undervoltage Lockout
■ Latching P.W.M. to Prevent Multiple Pulses
■ Dual Source/Sink Output Drivers

High Reliability Features
Following are the high reliability features of SG1525A and SG1527A:
■ Available to MIL-STD-883, ¶ 1.2.1
■ MIL-M38510/12602BEA - JAN1525AJ
■ MIL-M38510/12604BEA - JAN1527AJ
■ MSC-AMS level “S” Processing Available