CAT5120, CAT5121, CAT5122

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APPLICATIONS INFORMATION

The devices are intended for circuits requiring digitally

controlled adjustable resistance, such as LCD contrast

control, where voltage biasing adjusts the display contrast.

Alternative Positive LCD Bias Control

Use an op amp to provide buffering and gain on the output

of the CAT5120. Connect the mechanical potentiometer to

the positive input of a noninverting op amp (Figure 9) to

select a portion of the input signal by digitally controlling the

wiper terminal. Figure 10 shows a similar circuit for the

CAT5121.

Adjustable Gain

Figures 11 and 12 show how to use the variable resistor to

digitally adjust the gain of a noninverting op amp

configuration. Connect the CAT5121 in series with a resistor

to ground to form the adjustable gain control of a

noninverting amplifier. The devices have a low 5 ppm/C

ratiometric tempco that allows for a very stable adjustable

gain configuration over temperature.

30 V

W

L

H

+5 V

30 V

L

H

+5 V

L

H

L

H

W

CAT5120

CAT5121

CAT5121

CAT5120

Figure 9. Positive LCD Bias Control

Figure 10. Positive LCD Bias Control

Figure 11. Adjustable Gain Circuit

Figure 12. Adjustable Gain Circuit