CAT5132
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12
Potentiometer Operation
Power−On
The CAT5132 is a 128−position, digital controlled
potentiometer. When applying power to the CAT5132, VCC
must be supplied prior to or simultaneously with V+. At the
same time, the signals on RH, RW and RL terminals should
not exceed V+. If V+ is applied before VCC, the electronic
switches of the DPP are powered in the absence of the switch
control signals, that could result in multiple switches being
turned on. This causes unexpected wiper settings and
possible current overload of the potentiometer. When VCC
is applied 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.
At power−down, it is recommended to turn−off first the
signals on RH, RW and RL, followed by V+ and, after that,
VCC, in order to avoid unexpected transmissions of the
wiper and uncontrolled current overload of the
potentiometer.
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 10 kW potentiometer
~79 W is the resistance between each wiper position.
However in addition to the ~79 W for each resistive segment
of the potentiometer, a wiper resistance offset must be
considered. Table 19 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 10 kW
example. However resistance between each wiper position
for the 50 kW version will be ~395 W and for the 100 kW
version will be ~790 W.
Table 19. POTENTIOMETER RESISTANCE AND
WIPER RESISTANCE OFFSET EFFECTS
Position Typical RW to RL Resistance for 10 kW DPP
00 70 W or 0 W + 70 W
01 149 W or 79 W + 70 W
63 5,047 W or 4,977 W + 70 W
127 10,070 W or 10,000 W + 70 W
Position Typical RW to RH Resistance for 10 kW DPP
00 10,070 W or 10,000 W + 70 W
64 5,047 W or 4,977 W + 70 W
126 149 W or 79 W + 70 W
127 70 W or 0 W + 70 W