One-Time Programmable, Linear-Taper Digital

Potentiometers

10

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Applications Information

Use the MAX5527/MAX5528/MAX5529 in applications

requiring digitally controlled adjustable resistance,

such as LCD contrast control where voltage biasing

adjusts the display contrast, or for programmable filters

with adjustable gain and/or cutoff frequency.

Positive LCD Bias Control

Figures 7 and 8 show an application where the voltage-

divider or variable resistor is used to make an adjustable,

positive LCD bias voltage. The op-amp provides buffer-

ing and gain to the resistor-divider network made by the

potentiometer (Figure 7), or to a fixed resistor and a

variable resistor (Figure 8).

Programmable Filter

Figure 9 shows the configuration for a 1st-order pro-

grammable filter. The gain of the filter is adjusted by

R2, and the cutoff frequency is adjusted by R3. Use the

following equations to calculate the gain (G), and the

decade below the wiper -3dB bandwidth.

Adjustable Voltage Reference

Figure 10 shows the MAX5527/MAX5528/MAX5529

used as the feedback resistors in an adjustable-voltage

reference application.

G

R

R

f

xR xC

C

=+

=

1

1

2

1

23

π

30V

5V

W

H

L

MAX5527

MAX5528

MAX5529

Figure 7. Positive LCD Bias Control Using a Voltage-Divider

30V

5V

W

H

L

MAX5527

MAX5528

MAX5529

Figure 8. Positive LCD Bias Control Using a Variable Resistor

R1

W

H

L

R2

R3

H

W

L

C

MAX5527

MAX5528

MAX5529

5V

Figure 9. Programmable Filter

W

H

L

MAX6160

+5V

GND

OUT

ADJ

100k

Ω

FOR THE MAX5527

Ω)

50k

Ω

FOR THE MAX5528

Ω)

MAX5527

MAX5528

MAX5529

10k

Ω

FOR THE MAX5529

Ω)

Figure 10. Adjustable Voltage Reference