© 2007 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FSQ211 Rev. 1.0.0

3

Pin Assignments

1

2

3

45

6

7

8

GND

Vcc

Vfb

NC

Vstr

Drain

Drain

Drain

Figure 3.

Pin Configuration (Top View)

Pin Definitions

Pin

Name

Description

1

GND

Ground.

SenseFET source terminal on primary side and internal control ground.

2

VCC

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 Block Diagram). It

is not until VCC reaches the UVLO upper threshold (9V), that the internal start-up switch opens

and device power is supplied via the auxiliary transformer winding.

3

VFB

Feedback

. Inverts input to the PWM comparator with its normal input level between 0.5V and

2.5V. It has a 0.4mA current source connected internally, while a capacitor and opto-coupler

are typically connected externally. A feedback voltage of 4.5V triggers overload protection

(OLP). There is a time delay while charging external capacitor CFB from 3V to 4.5V using an

internal 5µA current source. This time delay prevents false triggering under transient

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

4

NC

No Connection

.

5

Vstr

Start-up

. This pin connects directly to the rectified AC line voltage source. At start-up, the

internal switch supplies internal bias and charges an external storage capacitor placed

between the VCC pin and ground. Once the VCC reaches 9V, the internal switch stops charging

the capacitor.

6,7,8

Drain

SenseFET 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.