DH321 데이터 시트보기 (PDF) - Fairchild Semiconductor

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DH321

Green Mode Fairchild Power Switch (FPS™)

Fairchild Semiconductor 

Pin Definitions

FSDH321, FSDL321

Pin Number

1

2

3

4

5

6, 7, 8

Pin Name

GND

Vcc

Vfb

Ipk

Vstr

Drain

Pin Function Description

Sense FET source terminal on primary side and internal control ground.

Positive supply voltage input. Although connected to an auxiliary transform-

er winding, current is supplied from pin 5 (Vstr) via an internal switch during

startup (see Internal Block Diagram section). It is not until Vcc reaches the

UVLO upper threshold (12V) that the internal start-up switch opens and de-

vice power is supplied via the auxiliary transformer winding.

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 op-

tocoupler are typically connected externally. A feedback voltage of 6V trig-

gers over load protection (OLP). There is a time delay while charging

between 3V and 6V using an internal 5uA current source, which prevents

false triggering under transient conditions but still allows the protection

mechanism to operate under true overload conditions.

Pin to adjust the current limit of the Sense FET. The feedback 0.9mA current

source is diverted to the parallel combination of an internal 2.8kΩ resistor

and any external resistor to GND on this pin to determine the current limit.

If this pin is tied to Vcc or left floating, the typical current limit will be 0.7A.

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

12V, the internal switch is disabled.

The Drain pin is designed to connect directly to the primary lead of the trans-

former and is capable of switching a maximum of 650V. Minimizing the

length of the trace connecting this pin to the transformer will decrease leak-

age inductance.

Pin Configuration

8DIP

8LSOP

GND 1

Vcc 2

Vfb 3

Ipk 4

8 Drain

7 Drain

6 Drain

5 Vstr

Figure 3. Pin Configuration (Top View)

3

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