CAT5120 Datasheet, PDF (4/12 Pages) Catalyst Semiconductor – 16-Tap MiniPot Digitally Programmable Potentiometers with 2-Wire Interface

CAT5120, CAT5121, CAT5122
FUNCTIONAL DESCRIPTION
The CAT5120/5121/5122 consist of a fixed resistor and
a wiper contact with 16-tap points that are digitally
controlled through a 2-wire up/down serial interface.
Three end-to-end resistance values are available: 10 kΩ,
50 kΩ and 100 kΩ.
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 C¯¯S is low.
The C¯¯S and U/D¯ inputs control the position of the
wiper along the resistor array. When C¯¯S 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 C¯¯S 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 C¯¯S 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.
CS
t CU
U/D
W
t IL
t CI
t IH
t SETTLE
Note: "W" is not a digital signal. It represents wiper transitions.
Figure 1. Serial Interface Timing Diagram, Increment Mode
t IC
t SETTLE
CS
t CU
t IC
t IH
U/D
t IL
t CI
W
t SETTLE
t SETTLE
Note: "W" is not a digital signal. It represents wiper transitions.
Figure 2. Serial Interface Timing Diagram, Decrement Mode
Doc. No. MD-2121 Rev. G
4
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Characteristics subject to change without notice