CAT5136 Datasheet, PDF (8/11 Pages) ON Semiconductor – Digital Potentiometers (POTs) with 128 Taps and I2C Interface

CAT5136, CAT5137, CAT5138
Table 12. READ OPERATION
CAT5136 and CAT5137
1st byte
SLAVE
ADDRESS
2nd byte
ADDRESS
BYTE
3rd byte
SLAVE ADDRESS
R
4th byte
OUTPUT DATA BYTE
S 0 1 0 1 1 1 0 0 A 0 0 0 0 0 0 0 0 A S 0 1 0 1 1 1 0 1 A 0 D6 D5 D4 D3 D2 D1 D0 NA P
CAT5138
1st byte
SLAVE
ADDRESS
2nd byte
ADDRESS
BYTE
3rd byte
SLAVE ADDRESS
R
4th byte
OUTPUT DATA BYTE
S 0 1 1 1 1 1 0 0 A 0 0 0 0 0 0 0 0 A S 0 1 1 1 1 1 0 1 A 0 D6 D5 D4 D3 D2 D1 D0 NA P
POTENTIOMETER OPERATION
CAT5136, CAT5137, CAT5138 are a family of a
128-position, digital controlled potentiometers. When V_DD
is applied, the device automatically turns on at the mid-point
wiper location (64).
At power-down, it is recommended to turn-off first the
signals on RH, RW and RL, followed by VDD, in order to
avoid unexpected transitions 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 50 kW
potentiometer ~390 W is the resistance between each wiper
position. However in addition to the ~390 W for each
resistive segment of the potentiometer, a wiper resistance
offset must be considered. Table 13 shows the effect of this
value and how it would appear on the wiper terminal.
Table 13. POTENTIOMETER RESISTANCE AND WIPER RESISTANCE OFFSET EFFECTS
Position
Typical RW to RL Resistance for 50 kW Digital Potentiometer
00
70 W or 0 W + 70 W
01
460 W or 390 W + 70 W
63
24,870 W or 24,800 W + 70 W
127
50,070 W or 50,000 W + 70 W
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