CAT5126_13 Datasheet, PDF (6/9 Pages) ON Semiconductor – One‐time Digital 32‐tap Potentiometer (POT)

CAT5126
If the intent is to program the device to a specific wiper
position and not to allow further adjustments, then six
programming pulses are required (as opposed to five), as
shown in Figure 8. The sixth pulse locks the wiper position
and disables the serial interface. This also allows U/D and
CS to float without any increase in supply current. Once the
lockout bit is set, no further adjustment to the potentiometer
is possible, effectively changing the potentiometer into a
fixed resistor-divider (Table 4).
It is recommended that the user either use six CS pulses
(convert to a fixed voltage-divider) or five pulses (program
the initial power-up value of the device, but still be able to
adjust the wiper). If the device is programmed with five
pulses and later it is desired to disable the interface (convert
to a fixed voltage-divider), then care must be taken to ensure
that the wiper is in the same position as it was originally set
to (when programmed with five pulses). The full six
programming pulses must be applied. Note that once the
six-pulse program occurs, no further programming is
possible.
Table 4. ONE−TIME PROGRAMMING MODE
Mode
Power Up Position
Factory Default
At midscale
Programming with 5 pulses at the midscale
position
At midscale
Programming with 5 pulses different from
midscale position – only once
At the new programmed
position
Programming with 5 pulses if the power up
position was changed before
At the previous
programmed position
Programming with 6 pulses if the tap
position is at midscale
Midscale position forever
Programming ONLY with 6 pulses if the tap
position is different from midscale position
At the new programmed
position
Interface
Active
Active
Active
Active
I²C interface active
till power down
I²C interface active
till power down
Operation
Programming allowed
Programming allowed
No further change in power-up
position allowed
None
I²C interface disable after next
power-up
I²C interface disable after next
power-up
U/D
10 V
V_PP
0V
CS
t_CH
t_CL
t_CP
t_PH
t_PC
5 BITS PROGRAM WIPER POSITION OPTIONAL LOCKOUT BIT
Figure 8. One Time Program Mode Serial Interface Timing Diagram
5. If CAT5126 is Programmed with less than 5 pulses, it does not change the Power-up recall position.
6. During internal power-up the wiper is forced to miscale; thereafter the wiper is set at the stored position.
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