6
FN8180.4
July 18, 2014
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Instructions and Programming
The INC, U/D and CS inputs control the movement of the wiper
along the resistor array. With CS
set LOW, the device is
selected and enabled to respond to the U/D
and INC inputs.
HIGH-to-LOW transitions on INC
will increment or decrement
(depending on the state of the U/D
input) a 5-bit counter. The
output of this counter is decoded to select one of thirty-two
wiper positions along the resistive array.
The value of the counter is stored in nonvolatile memory
whenever CS
transitions HIGH while the INC input is also
HIGH. In order to avoid an accidental store during power-up,
CS
must go HIGH with V
CC
during initial power-up. When
performing multiple write operations, V
CC
must not decrease
by more than 150mV from its initial value. When left open, the
CS
pin is internally pulled up to V
CC
by an internal 30k resistor.
The system may select the X93154, move the wiper and
deselect the device without having to store the latest wiper
position in nonvolatile memory. After the wiper movement is
performed as previously described and once the new position
is reached, the system must keep INC
LOW while taking CS
HIGH. The new wiper position will be maintained until changed
by the system or until a power-up/down cycle recalled the
previously stored data. In order to recall the stored position of
the wiper on power-up, the CS
pin must be held HIGH.
This procedure allows the system to always power-up to a
preset value stored in nonvolatile memory; then during system
operation minor adjustments could be made. The adjustments
might be based on user preference, system parameter
changes due to temperature drift, or other system trim
requirements.
The state of U/D
may be changed while CS remains LOW. This
allows the host system to enable the device and then move the
wiper up and down until the proper trim is attained.
Symbol Table
Applications Information
Electronic digitally controlled (XDCP) potentiometers provide
three powerful application advantages:
1. The variability and reliability of a solid-state potentiometer
2. The flexibility of computer-based digital controls
3. The retentivity of nonvolatile memory used for the storage
of multiple potentiometer settings or data
.
Mode Selection
CS INC U/D MODE
L H Wiper Up
L L Wiper Down
H X Store Wiper Position
H X X Standby Current
L X No Store, Return to Standby
L H Wiper Up (not recommended)
L L Wiper Down (not recommended)
Mode Selection
CS INC U/D MODE
WAVEFORM INPUTS OUTPUTS
Must be
steady
Will be
steady
May change
from Low to
High
Will change
from Low to
High
May change
from High to
Low
Will change
from High to
Low
Don’t Care:
Changes
Allowed
Changing:
State Not
Known
N/A Center Line
is High
Impedance
V
R
FIGURE 1. TWO TERMINAL VARIABLE RESISTOR. VARIABLE CURRENT
I
X93154
