FSL518H, FSL538H, FSL518A, FSL538A

www.onsemi.com

3

Figure 2. Internal Block Diagram

OSC

LINE

DRAIN

FB

Gate Driver

VCC

PWM

S

R

Q

SQ

R

TSD

GND

Frequency

Reduction

Soft

Start

LEB

Slope

Compensation

HV Current

Source

COMP

E/A

Initial Setting and

Line Detection

Brown−out

AOCP

Logic

Protection

Brown− out

LOVP

R

3R

Q

Q

START/ STOP

S

PIN FUNCTION DESCRIPTION

Pin No.

Pin Name

Pin Function

Description

1

GND

Ground

SENSEFET source terminal and internal controller ground.

2

VCC

Power Supply

This pin is connected to an external capacitor and provides internal operating current of

the IC. It also includes an auto-recovery over-voltage protection.

3

FB

Feedback

This pin is connected to the input of transconductance amplifier for regulating output volt-

age of the power converter. If transconductance amplifier is not used, connect FB to

GND.

4

COMP

Feedback-Loop

Compensation

Control-loop compensation. For opto-coupler feedback, connect COMP to opto coupler

directly.

5

LINE

Brown in/out, LOVP,

Burst-mode Setting

For line detection(Line OVP, Brown in/out), this pin needs to be connected to the high-

voltage DC link through voltage divider. And it’s also multiple-function pin for burst−mode

adjustment.

7,8

DRAIN

MOSFET Drain

High-voltage power MOSFET drain connection. In addition, during startup and protection

mode, the internal high-voltage current source supplies internal bias current and charges

the external capacitor connected to the VCC pin.