© 1997 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

MICROPOWER INVERTING

DC-DC CONVERTER

SC1652

January 29, 1998

TYPICAL APPLICATION INFORMATION

The typical application circuit generates an adjustable negative voltage for

contrast bias of LCD displays. Efficiency and output power can be opti-

mized by using the appropriate inductor and switch. The following formulas

provide a guideline for determining the optimal component values:

()

()

.

Ohm

in

R

,

H

in

L

,

Ampere

in

I

,

Volt

in

V

,

Volt

in

V

:

units

where

,

8

.

0

V

L

3

R

10

and

V

I

200

I

at

V

4

.

0

V

V

I

200

I

V

V

V

:

PNP

V

I

V

V

15

.

0

1

.

11

L

B

OUT

OUT

B

OUT

C

)

SAT

(

CE

OUT

)

MAX

(

C

OUT

CEO

OUT

OUT

µ

−

×

×

≅

=

β

×

=

<

×

≥

+

>

×

×

×

−

=

+

+

+

+

+

+

+