Data Sheet

© 2007 Fairchild Semiconductor Corporation www.fairchildsemi.com
FSQ0365, FSQ0265, FSQ0165, FSQ321 • Rev. 1.0.6 4
FSQ0365/0265/0165/321 — Green Mode Fairchild Power Switch (FPS™) for Valley Switching Converter
Pin Assignments
Figure 3. Pin Configuration (Top View)
Pin Definitions
Pin# Name Description
1 GND SenseFET source terminal on primary side and internal control ground.
2 V
CC
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 Figure 2).
It is not until V
CC
reaches the UVLO upper threshold (12V) that the internal startup switch
opens and device power is supplied via the auxiliary transformer winding.
3 Vfb
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 opto-coupler are typically
connected externally. There is a time delay while charging external capacitor C
fb
from 3V
to 6V using an internal 5A current source. This delay prevents false triggering under
transient conditions, 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 capacitor are needed to make delay to match valley point. The threshold of
the internal sync comparator is 0.7V/0.2V.
5 Vstr
This pin is connected to the rectified AC line voltage source. At startup, the internal switch
supplies internal bias and charges an external storage capacitor placed between the Vcc
pin and ground. Once the V
CC
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 650V. Minimizing the length of the trace
connecting these pins to the transformer decreases leakage inductance.