CAT5126_08 Datasheet, PDF (6/11 Pages) Catalyst Semiconductor – One-Time Digitally Programmable 32-Tap Potentiometer

CAT5126
DETAILED DESCRIPTION
The CAT5126 devices are 10kΩ/50kΩ/100kΩ (end-to-
end resistance) digitally controlled potentiometers.
They have 32-tap positions that are accessible to the
wiper along the resistor array between R_H and R_L.
The wiper (R_W) position is adjusted sequentially
through the tap positions using a simple I²C interface.
These digital potentiometers have an optional one-time
programmable feature that sets the POR position of the
wiper. The I²C interface can then be disabled,
permanently preventing unwanted adjustment.
DIGITAL INTERFACE OPERATION
The CAT5126 devices have two modes of operation
when the serial interface is active: increment mode
and decrement mode. The serial interface is only
active when C¯¯S¯ is low.
The C¯¯S¯ and U/D¯ inputs control the position of the
wiper along the resistor array. When C¯¯S¯ transitions
from high to low, the part goes into increment mode if
U/D¯ is high (Figure 1), and into decrement mode if
U/D¯ is low (Figure 2). Once the mode is set, the
device remains in that mode until C¯¯S¯ goes high. A
low-to-high transition at the U/D¯ increments or
decrements the wiper position depending on the
current mode.
The value of the counter is then stored and the wiper
position is maintained till the device is Powered down.
The wiper performs a make-before-break transition,
ensuring that there is never an open circuit during a
transition from one resistor tap to another. When the
wiper is at either end (max/min) of the resistor array,
additional transitions in the direction of the endpoint
do not change the counter value (the counter does not
wrap around).
One-Time Programming
The factory-set default position of the wiper on power-
up is tap 16. However, the power-up position can be
changed once using the one-time programming feature.
After the wiper is moved to the desired position, the
programming sequence is initiated by setting U/D¯ high,
applying 10V to V_PP, and then taking ^{¯C¯S¯} low. Five
pulses on ^{¯C¯S¯} (consisting of ^{¯C¯S¯} starting from low and
going high for t_CH and then low for t_CL) program the
device (Figure 3). The programming voltage should
then be taken to zero. After the device is programmed,
V_PP can be set to zero or be allowed to float. The wiper
position is still adjustable, but always returns to this
programmed position on power-up.
V_DD
t_UP
CS
t_CU
t_CI
t_IL
t_IH
t_IC
U/D
t_IW
V_W
Figure 1. Increment Mode Serial Interface Timing Diagram
V_DD
CS
U/D
V_W
t_UP
t_CU
t_CI
t_IH
t_IL
t_IC
t_IW
Doc. No. MD-2129 Rev. B
Figure 2. Decrement Mode Serial Interface Timing Diagram
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© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice