CAT5132ZI-10 Datasheet, PDF(11/12 Page) ON Semiconductor – 16 Volt Digital Potentiometer (POT) with 128 Taps and I2C Interface

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CAT5132ZI-10 Datasheet, PDF (11/12 Pages) ON Semiconductor – 16 Volt Digital Potentiometer (POT) with 128 Taps and I2C Interface

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CAT5132

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 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

Digital POT

70 W or

0 W + 70 W

149 W or

79 W + 70 W

5,047 W or

4,977 W + 70 W

127

10,070 W or

10,000 W + 70 W