FSDH321, FSDL321

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3

Table 2. PIN DEFINITIONS

Pin Number

Pin Name

Pin Function Description

1

GND

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 sup-

plied 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 (12 V) that the internal start−up 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 0.9 mA current

source connected internally while a capacitor and optocoupler are typically connected externally.

A feedback voltage of 6 V triggers over load protection (OLP). There is a time delay while charging

external capacitor Cfb from 3 V to 6 V using an internal 5

mA current source. This time delay prevents

false triggering under transient conditions, but still allows the protection mechanism to operate under

true overload conditions.

4

Ipk

This pin adjusts the peak current limit of the SENSEFET. The feedback 0.9 mA current source is di-

verted to the parallel combination of an internal 2.8 k

W resistor and any external resistor to GND on

this pin to determine the peak current limit. If this pin is tied to Vcc or left floating, the typical peak

current limit will be 0.7 A.

5

Vstr

This pin connects directly 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 12 V, 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 650 V. Minimizing the length of the trace connecting these pins to the

transformer will decrease leakage inductance.

ABSOLUTE MAXIMUM RATINGS (Ta = 25

°C, unless otherwise specified)

Symbol

Parameter

Ratings

Unit

VDRAIN

Drain Pin Voltage

650

V

VSTR

Vstr Pin Voltage

650

V

VDG

Drain−Gate Voltage

650

V

VGS

Gate−Source Voltage

±20

V

IDM

Drain Current Pulsed (Note 4)

1.5

A

ID

Continuous Drain Current (TC = 25°C)

0.7

A

Continuous Drain Current (TC = 100°C)

0.32

EAS

Single Pulsed Avalanche Energy (Note 5)

10

mJ

VCC

Supply Voltage

20

V

VFB

Feedback Voltage Range

−0.3 to VCC

V

PD

Total Power Dissipation

1.40

W

TJ

Operating Junction Temperature

Internally limited

°C

TA

Operating Ambient Temperature

−25 to 85

°C

TSTG

Storage Temperature

−55 to 150

°C

Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality

should not be assumed, damage may occur and reliability may be affected.

4. Repetitive rating: Pulse width is limited by maximum junction temperature

5. L = 24 mH, TJ = 25°C

THERMAL CHARACTERISTICS (Ta = 25

°C, unless otherwise specified)

Symbol

Parameter

Ratings

Unit

8DIP

qJA

Junction−to−Ambient Thermal (Note 6)

88.84

°C/W

qJC

Junction−to−Case Thermal (Note 7)

13.94

°C/W

NOTE:

All items are tested with the standards JESD 51−2 and 51−10 (DIP).

6. Free standing with no heatsink; without copper clad

Measurement condition: Just before junction temperature TJ enters into OTP

7. Measured on the DRAIN pin close to plastic interface