NCP1280

http://onsemi.com

3

PIN DESCRIPTION

Pin

Name

Application Information

1

This pin is connected to the input voltage of the system. The voltage can be a rectified, filtered line voltage

or output of a power factor correction (PFC) front end. A constant current source supplies current from this

voltage is 700 V.

2

NC

Not Connected.

3

UV/OV

Provides protection under line undervoltage and overvoltage conditions. The built in voltage range is

X 2:1. If needed, the OV function can be disabled by a Zener from this pin to ground.

4

FF

regulation is improved.

5

CS

Overcurrent sense input. If the CS voltage exceeds 0.48 V or 0.57 V, the converter enters the Cycle by

Cycle or Cycle Skip current limit mode, respectively.

6

CSKIP

The capacitor connected between this pin and ground sets the Cycle Skip period. A soft−start sequence

follows at the conclusion of the fault period.

7

A single external resistor between this pin and GND sets the oscillator fixed frequency.

8

An external resistor between this pin and GND sets the voltage on the Max DC Comparator inverting

input. The duty cycle is limited by comparing the voltage on the Max DC Comparator inverting input to the

Feedforward Ramp.

9

SS

An internal 6.2

mA current source charges the external capacitor connected to this pin. The duty cycle is

limited during startup by comparing the voltage on this pin to the Oscillator Ramp.

10

The error signal from an external error amplifier, typically supplied through an optocoupler, is fed into this

input and compared to the Feedforward Ramp. A series diode and resistor offset the voltage on this pin

before it is applied to the PWM Comparator inverting input.

11

Precision 5.0 V reference output. Maximum output current is 6 mA.

12

transitions.

13

OUT2

Output of the PWM controller with leading and trailing edge overlap delay. OUT2 can be used to drive a

synchronous rectifier topology, an active clamp/reset switch, or both.

14

GND

Control circuit ground.

15

OUT1

Main output of the PWM controller.

16

Positive input supply voltage. This pin is connected to an external capacitor for energy storage. An

the IC via this pin, by means of an auxiliary winding.