CAT5121_13 Datasheet, PDF (5/11 Pages) ON Semiconductor – 16‐tap Digital Potentiometers (POTs)

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. Two end-to-end
resistance values are available: 10 kW and 50 kW.
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.
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 7 and 8).
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.
Digital Interface Operation
The devices 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
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
t_IL
U/D
t_CI
t_IH
t_SETTLE
W
Note: “W” is not a digital signal. It represents wiper transitions.
Figure 7. Serial Interface Timing Diagram, Increment Mode
t_IC
t_SETTLE
CS
t_CU
t_IC
t_IH
U/D
t_IL
W
t_CI
t_SETTLE
t_SETTLE
Note: “W” is not a digital signal. It represents wiper transitions.
Figure 8. Serial Interface Timing Diagram, Decrement Mode
http://onsemi.com
5