CAT5120, CAT5121, CAT5122

Doc. No. MD-2121 Rev. E

4

© Catalyst Semiconductor, Inc.

Characteristics subject to change without notice

FUNCTIONAL DESCRIPTION

The CAT5120/5121/5122 consist of a fixed resistor and

a wiper contact with 16-tap points that are digitally

controlled through a2-wire up/down serial interface.

Three end-to-end resistance values are available: 10kΩ,

50kΩ and 100kΩ.

The CAT5120 is designed to operate as a potentiometer.

In this configuration, the low terminal of the resistor array

is connected to ground (pin 2).

The CAT5122 performs as a variable resistor. In this

device, the wiper terminal and high terminal of the

resistor array is connected at pin 5. The CAT5121 is a

similar variable resistor, except the low terminal is

connected to pin 5.

Digital Interface Operation

The MiniPots have two modes of operation when the

serial interface is active: increment and decrement

mode. The serial interface is only active when CS

¯¯ is low.

The CS

¯¯ and U/D

¯ inputs control the position of the

wiper along the resistor array. When CS

¯¯ transitions

from high to low, the part will go into increment mode

if U/D

¯ input is high, and into decrement mode when

U/D

¯ input is low. Once the mode is set, the device will

remain in that mode until CS

¯¯ goes high again. A low-

to-high transition at the U/D

¯ pin will increment or

decrement the wiper position depending on the

current mode (Figures 1 and 2).

When the CS

¯¯ input transitions to high (serial interface

inactive), the value of the counter is stored and the

wiper position is maintained.

Note that when the wiper reaches the maximum (or

minimum) tap position, the wiper will not wrap around

to the minimum (or maximum) position.

Power-On Reset

All parts in this family feature power-on reset (POR)

circuitry that sets the wiper position to midscale at

power-up. By default, the chip is in the increment mode.

Figure 1. Serial Interface Timing Diagram, Increment Mode

Figure 2. Serial Interface Timing Diagram, Decrement Mode

CS

U/D

W

Note: "W" is not a digital signal. It represents wiper transitions.

CS

U/D

W

Note: "W" is not a digital signal. It represents wiper transitions.