Low-Power Digital Potentiometers

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5

Detailed Description

The MAX5160/MAX5161 consist of resistor arrays with

31 resistive elements. Thirty-two tap points are accessi-

ble to the wiper along the resistor string between H and

L. Logic inputs CS, U/D, and INC determine the posi-

tion of the wiper. With CS low and U/D high, a high-to-

low transition on INC increments the internal counter,

increasing the resistance between W and L. When both

CS and U/D are low, a high-to-low INC transition

decrements the internal counter, decreasing the resis-

tance between W and L. At either end (maximum or mini-

mum positions), additional transitions in the direction of

the end points will not change the counter value (the

counter will not wrap around).

The H and L terminals of the MAX5160 are similar to the

two end terminals of a mechanical potentiometer. The

tap W is equivalent to the variable tap (wiper) of the

potentiometer.

The MAX5161 is similar to the MAX5160 except that CS

internally connects to ground and the wiper terminal (W)

is shorted to the high terminal (H). The MAX5161 acts as

a variable resistor (a potentiometer with the wiper and

one end terminal shorted together).

The MAX5160/MAX5161 feature power-on reset circuit-

ry that sets the wiper position to midscale at power-up.

Applications Information

The MAX5160/MAX5161 are intended for circuits

requiring digitally controlled adjustable voltage or

adjustable gain, such as LCD contrast control, where

voltage biasing adjusts the display contrast.

Controlling a Switch-Mode

LCD Bias Generator

Figure 1 shows an application where the MAX5161 is

used with a MAX1771 to make an adjustable positive

LCD-bias circuit. The output of the MAX1771 is a posi-

tive voltage that is digitally controlled through the

MAX5160/MAX5161. Similarly, Figure 2 shows the

application of the MAX5161 in a digitally controlled

negative LCD-bias circuit along with the MAX774/

MAX775/MAX776.

MAX1771

REF

SHDN

AGND

GND

N

MTD20N03HDL

7

EXT

CS

FB

L1

22

µH

D1

1N5817-22

C4

300

µF

C5

C3

0.1

µF

5

4

6

1

8

3

2

V+

C1

68

µF

AT 0.5A

R2

40m

Ω

C2

0.1

µF

R1

=

R2

+ 1

R1

=

(

R2

MAX5161

Figure 1. Adjustable Positive LCD Bias

MAX774

MAX775

MAX776

OUT

V+

SHDN

CS

FB

EXT

GND

P

7

8

C2

0.1

µF

R3

0.07

Ω

R1

R2

C1

150

µF

6

5

2

3

1

REF

4

Q1

Si9435

1N5822/

MBR340

L1

22

µH

C4

*

C3

0.1

µF

µF, 10V

MAX775, MAX776 = 120

µF, 20V

=

R2

,

=

R2

R1

5

µA (FOR 2% GAIN-SETTING ACCURACY)

MAX5161

Figure 2. Adjustable Negative LCD Bias