AS1507 datasheet(13/17 Pages) AMSCO

13 / 17 page

www.austriamicrosystems.com

Revision 1.00

13 - 17

AS1507

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

9 Application Information

The AS1507 is intended for circuits requiring digitally controlled adjustable resistance, such as LCD contrast control

(where voltage biasing adjusts the display contrast), or programmable filters with adjustable gain and/or cutoff fre-

quency.

Programmable Filter

Figure 25 shows the configuration for a 1st-order programmable filter.

The DC gain of the filter is adjusted by R2 and can be calculated as:

G = 1 + (R1/R2)(EQ 1)

The cutoff frequency (fC) is adjusted by R3, and can be calculated as:

fC = 1/(2

π x R3 x C)

(EQ 2)

Figure 25. Programmable Filter Circuit

Offset Voltage and Gain Adjustment

Connect one potentiometer of the AS1507 to an op amp to nullify the offset voltage over the operating temperature

range. Use the second potentiometer in the feedback path to adjust the gain of the op amp (Figure 26).

Figure 26. Offset Voltage and Gain Adjustment Circuit

–

VIN

VOUT

CIN

AS1507

HIGHA

LOWA

HIGHB

WIPERB

LOWB

WIPERA

AS1507

–

HIGHA

LOWA

HIGHB

WIPERB

LOWB

WIPERA

AS1507 Datasheet(PDF) 13 Page - ams AG