2

LNK520

E

2/05

Pin Functional Description

DRAIN (D) Pin:

Power MOSFET drain connection. Provides internal operating

current for start-up. Internal current limit sense point for drain

current.

CONTROL (C) Pin:

Error amplifier and feedback current input pin for duty cycle

and current limit control. Internal shunt regulator connection

to provide internal bias current during normal operation. It is

also used as the connection point for the supply bypass and

auto-restart/compensation capacitor.

SOURCE (S) Pin:

Output MOSFET source connection for high voltage power

return. Primary side control circuit common and reference

point.

Figure 3. Pin Configuration.

Figure 2. Block Diagram.

PI-2777-032503

SHUTDOWN/

AUTO-RESTART

PWM

COMPARATOR

CLOCK

SAW

OSCILLATOR

INTERNAL

SUPPLY

5.6 V

4.7 V

SOURCE

S

R

Q

DMAX

-

+

CONTROL

-

+

5.6 V

Z C

VC

+

-

EDGE

0

1

HYSTERETIC

THERMAL

SHUTDOWN

LEADING

EDGE

BLANKING

CURRENT

LIMIT

ADJUST

LOW

FREQUENCY

OPERATION

SHUNT REGULATOR/

ERROR AMPLIFIER

+

-

DRAIN

IDCS

CURRENT LIMIT

COMPARATOR

RE

÷ 8

PI-3790-121503

S

D

S

S

S

C

5

7

8

S

4

2

3

1

P Package (DIP-8B)

G Package (SMD-8B)

LNK520