X93256_08 Datasheet, PDF (6/7 Pages) Intersil Corporation – Dual Digitally Controlled Potentiometers(XDCPs™)

X93256
section operates just like an up/down counter. The output of
this counter is decoded to turn on a single electronic switch
connecting a point on the resistor array to the wiper output.
Under the proper conditions, the contents of the counter can
be stored in nonvolatile memory and retained for future use.
Each resistor array is comprised of 31 individual resistors
connected in series. At either end of the array and between
each resistor is an electronic switch that transfers the
connection at that point to the wiper.
Each wiper, when at either fixed terminal, acts like its
mechanical equivalent and does not move beyond the last
position. That is, the counter does not wrap around when
clocked to either extreme.
If the wiper is moved several positions, multiple taps are
connected to the wiper for t_IW (INC to V_W change). The
2-terminal resistance value for the device can temporarily
change by a significant amount if the wiper is moved several
positions.
When the device is powered-down, the last wiper position
stored will be maintained in the nonvolatile memory for each
potentiometer. When power is restored, the contents of the
memory are recalled and each wiper is set to the value last
stored.
Instructions and Programming
The INC, U/D and CS inputs control the movement of the
pertaining wiper along the resistor array. With CS set LOW
the pertaining potentiometer 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 each CS transitions HIGH while the pertaining
INC input is also HIGH. In order to avoid an accidental store
during power-up, each CS must go HIGH with V_CC during
initial power-up. When left open, each CS pin is internally
pulled up to V_CC by an internal 30k resistor.
The system may select the X93256, move any 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 each wiper up and down until the proper trim is
attained.
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)
Symbol Table
WAVEFORM INPUTS
OUTPUTS
Must be
steady
May change
from Low to
High
May change
from High to
Low
Don’t Care:
Changes
Allowed
N/A
Will be
steady
Will change
from Low to
High
Will change
from High to
Low
Changing:
State Not
Known
Center Line
is High
Impedance
6
FN8188.2
February 1, 2008