LX1681/1682

PRODUCT DA T ABOOK 1996/1997

Copyright © 1999

Rev. 1.0 5/99

4

V

FB

Voltage feedback — 1.25V reference is connected to a resistor divider to set desired

1

1

output voltage.

SS

Soft-start and hiccup capacitor pin. During start up the voltage of this pin controls the

2

2

output voltage. An internal 20k

Ω resistor and the external capacitor set the time constant

for soft-startup. Soft-start does not begin until the supply voltage exceeds the UVLO

threshold. When over-current occurs, this capacitor is used for timing hiccup.

The PWM can be disabled by pulling the SS pin below 0.3V.

GND

Ground for IC

43

TDRV

Gate drive for upper MOSFET

5

4

BDRV

Gate drive for lower MOSFET

5

V

C1

Separate supply for MOSFET gate drive. Connect to 12V

6

6

CS

Over-current set. Connect resistor between CS pin and the source of the upper MOSFET to

7

7

set current-limit point.

V

CC

IC supply voltage (nominal 5V) and high side drain sense voltage.

8

8

Pin

Pin Number

Name

Description

LX1681

LX1682

FUNCTIONAL PIN DESCRIPTION