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AS2916

PWM Controller

Pin Function Description

Pin Number

Function

Description

1

OUTB

This is the gate drive output for the Main FET. The totem pole

output has equivalent of an extra 10

Ω resistor to limit the FET

turn on speed and a pull down resistor to ensure the FET gate

is never open. No external circuitry except for the FET is

expected on this pin. The largest FET expected to be driven is

IRFBC40. If a larger power FET is used, a buffer might be

required.

2VCC

Positive supply for the IC. Absolute maximum rating is 20 V.

The running voltage shall be provided by the Auxiliary conver

tor.

3

REG

Output of 5 V series regulator.

4

SNSB

This is the Main convertor current sense pin. An external RC

filter from the Main power FET and slope compensation resis-

tor from the RAMP pin is all the expected external circuitry.

5

CMPB

This is the Main output control pin. An opto isolated control

signal from the secondary side error amplifier is buffered and

connected to the invert pin of the main output current mode

comparator. A pull-up current of 1 mA is provided so the only

external circuitry expected is a common emitter opto-isolator.

6

SS

This pin provides a 6 µA current source to linearly charge an

external capacitor. This spin is compared to the RAMP pin in

the soft start comparator, terminating output pulses when

RAMP goes above the SS voltage. While this pin is held low,

the main output is inhibited.

7

RAMP

This pin is a level-shifted and buffered oscillator waveform,

used to provide slope compensation for the Main and Auxiliary

converters. The pin also serves as the non-inverting input of

the soft-start comparator.

8

OSC

Oscillator frequency and maximum duty cycle are set by con-

necting the resistor (RT) to VREG and a capacitor (CT) to

ground.

9

WBL

Provides an FM modulation of the oscillator, approximately

±25% deviation frequency, at a modulation rate set by an exter-

nal cap at WBL. Shorting to GND eliminates modulation.

10

ON

This pin is used to remotely turn the main convertor ON/OFF

either for normal user application or for protection.

11

BOK

Bulk OK. This is a brownout protection feature. The pin moni-

tors the bulk voltage through a resistor divider. When BOK

exceeds 2.5 V a 50 µA current is sourced from the pin for hys-

teresis. When the pin drops below 2.5 V the hysteresis is

turned off and SS is pulled low,inhibiting the main output.

The Auxiliary output is not tied to BOK and will run as long as

there is sufficient bias voltage.