© 2006 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FSQ0365, FSQ0265, FSQ0165, FSQ321, FSQ311 Rev. 1.0.5

4

Pin Configuration

Figure 3. Pin Configuration (Top View)

Pin Definitions

Pin #

Name

Description

1

GND

SenseFET source terminal on primary side and internal control ground.

2Vcc

Positive supply voltage input. Although connected to an auxiliary transformer winding, current

is supplied from pin 5 (Vstr) via an internal switch during startup (see Internal Block Diagram

switch opens and device power is supplied via the auxiliary transformer winding.

3Vfb

The feedback voltage pin is the non-inverting input to the PWM comparator. It has a 0.9mA

current source connected internally while a capacitor and optocoupler are typically connected

externally. There is a time delay while charging external capacitor Cfb from 3V to 6V using an

internal 5

μA current source. This time delay prevents false triggering under transient condi-

tions but still allows the protection mechanism to operate under true overload conditions.

4

Sync

This pin is internally connected to the sync-detect comparator for valley switching. Typically the

voltage of the auxiliary winding is used as Sync input voltage and external resistors and capac-

itor are needed to make time delay to match valley point. The threshold of the internal sync

comparator is 0.7V/0.2V.

5Vstr

This pin is connected to the rectified AC line voltage source. At start-up the internal switch sup-

plies internal bias and charges an external storage capacitor placed between the Vcc pin and

ground. Once the Vcc reaches 12V, the internal switch is opened.

6,7,8

Drain

The drain pins are designed to connect directly to the primary lead of the transformer and are

capable of switching a maximum of 700V. Minimizing the length of the trace connecting these

pins to the transformer will decrease leakage inductance.

GND

Vcc

Sync

Vstr

8-DIP

Vfb

D

D

D

FSQ0365RN Rev.01

8-LSOP

V