Pin Description

Pin Name

Pin

Number

Description

Application Information

V

IN

1

Source Input Voltage

Input to start-up regulator. Input range 14 to 100 Volts.

V

FB

2

Inverting input to the error amplifier The non-inverting input is internally connected to a 1.25 Volt

reference.

COMP

3

Output to the error amplifier

There is an internal 5K resistor pull-up on this pin. The error

amplifier provides an active sink.

Vcc

4

Output from the internal high

voltage series pass regulator. The

regulation setpoint is 7.7 Volts.

If an auxiliary winding raises the voltage on this pin above the

regulation setpoint the internal series pass regulator will

shutdown, reducing the IC power dissipation.

OUT1

5

Output of the PWM controller

Alternating PWM output gate driver.

OUT2

6

Output of the PWM controller

Alternating PWM output gate driver.

GND

7

Return

Ground

CS

8

Current sense input

Current sense input for current mode control and current limit

sensing. Using separate dedicated comparators, if CS exceeds

0.5 Volt the outputs will go into Cycle by Cycle current limit. If CS

exceeds 0.625V the outputs will be disabled and a softstart

commenced.

RT

9

Oscillator timing resistor pin and

synchronization input.

An external resistor sets the oscillator frequency. This pin will

also accept synchronization pulses from an external oscillator.

SS

10

Dual purpose Softstart and

Shutdown pin

A 10µA current source and an external capacitor set the softstart

timing length. The controller will enter a low power state if the SS

pin is pulled below the typical shutdown threshold of 0.45V.

www.national.com

3