AD5220

–9–

REV.

PROGRAMMING THE POTENTIOMETER DIVIDER

Voltage Output Operation

The digital potentiometer easily generates an output voltage

proportional to the input voltage applied to a given terminal.

For example connecting A Terminal to +5 V and B Terminal to

ground produces an output voltage at the wiper which can be

any value starting at zero volts up to 1 LSB less than +5 V. Each

LSB of voltage is equal to the voltage applied across terminals

AB divided by the 128-position resolution of the potentiometer

divider. The general equation defining the output voltage with

respect to ground for any given input voltage applied to termi-

nals AB is:

(1)

D represents the current contents of the internal UP/DOWN

counter.

Operation of the digital potentiometer in the divider mode re-

sults in more accurate operation over temperature. Here the

output voltage is dependent on the ratio of the internal resistors,

not the absolute value, therefore, the drift improves to 20 ppm/

°C.

APPLICATIONS INFORMATION

The negative-edge sensitive CLK pin does not contain any

internal debounce circuitry. This standard CMOS logic input

responds to fast negative edges and needs to be debounced

externally with an appropriate circuit designed for the type of

switch closure device being used. Good performance results at

the CLK input pin when the negative logic transition has a

minimum slew rate of 1 V/

µs. A wide variety of standard circuits

can be used such as a one-shot multivibrator, Schmitt Triggered

gates, cross coupled flip-flops, or RC filters to drive the CLK

pin with uniform negative edges. This will prevent the digital

potentiometer from skipping output codes while counting due to

switch contact bounce.

A