CAT5126 Datasheet, PDF (7/11 Pages) Catalyst Semiconductor – One-Time Digitally Programmable 32 Tap Potentiometer

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 3. The sixth
pulse locks the wiper position and disables the serial
interface. This also allows U/D¯ and C¯¯S¯ 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 1).
It is recommended that the user either use six C¯¯S¯
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 1. 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
At the previous
power up position was changed before 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
2-wire interface
active till power
down
2-wire interface
active till power
down
Operation
Programming allowed
Programming allowed
No further change in power-
up position allowed
None
2-wire interface disable
after next power-up
2-wire interface disable
after next power-up
Figure 3: One Time Program Mode Serial Interface Timing Diagram
U/D
10V
V_PP
0V
CS
t_CH
t_CL
t_CP t_PH
t_PC
5 BITS PROGRAM WIPER POSITION
OPTIONAL LOCKOUT BIT
Notes:
(1) If CAT5126 is Programmed with less than 5 pulses, it does not change the Power-up recall position.
(2) During internal power-up the wiper is forced to miscale; thereafter the wiper is set at the stored position.
© 2007 Catalyst Semiconductor, Inc.
7
Characteristics subject to change without notice
Doc. No. 2129 Rev. A