CAT5132 Datasheet, PDF (11/13 Pages) Catalyst Semiconductor – 15 Volt Digitally Programmable Potentiometer (DPP) with 128 Taps and 2-wire Interface

CAT5132
POTENTIOMETER OPERATION
Power-On
The CAT5132 is a 128-position, digital controlled
potentiometer. At power-up the device turns on at the
mid-point wiper location (64) until the wiper register can
be loaded with the nonvolatile memory location previously
stored in the device. After the nonvolatile memory data
is loaded into the wiper register the wiper location will
change to the previously stored wiper position.
The end-to-end nominal resistance of the potentiometer
has 128 contact points linearly distributed across the
total resistor. Each of these contact points is addressed
by the 7 bit wiper register which is decoded to select one
of these 128 contact points.
Each contact point generates a linear resistive value
between the 0 position and the 127 position. These
values can be determined by dividing the end-to-end
value of the potentiometer by 127. In the case of the
10kΩ potentiometer~79Ω is the resistance between
each wiper position. However in addition to the ~79Ω for
each resistive segment of the potentiometer, a wiper
resistance offset must be considered. Table 8 shows the
effect of this value and how it would appear on the wiper
terminal.
This offset will appear in each of the CAT5132 end-to-
end resistance values in the same way as the 10kΩ
example. However resistance between each wiper
position for the 50kΩ version will be ~395Ω and for the
100kΩ version will be ~790Ω.
Table 8. Potentiometer Resistance and Wiper
Resistance Offset Effects
Position
00
01
63
127
Typical R_W to R_L Resistance for
10kΩ DPP
70Ω or
0Ω + 70Ω
149Ω or
79Ω + 70Ω
5,047Ω or
4,977Ω + 70Ω
10,070Ω or
10,000Ω + 70Ω
Position
00
64
126
127
Typical R_W to R_H Resistance for
10kΩ DPP
10,070Ω or
10,000Ω + 70Ω
5,047Ω or
4,977Ω + 70Ω
149Ω or
79Ω + 70Ω
70Ω or
0Ω + 70Ω
© 2005 by Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
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Doc No. 25092, Rev. 00