X93254 Datasheet, PDF (6/10 Pages) Intersil Corporation – Dual Digitally Controlled Potentiometers

X93254
PIN DESCRIPTIONS
(In the text, CS, INC, U/D, R_H and R_L are used to refer
to either CS₁ or CS₂, etc. Note: These signals can be
applied independently or at the same time.)
R_H and R_L
The R_H and R_L pins of the X93254 are equivalent to
the fixed terminals of a mechanical potentiometer. The
minimum voltage is V_SS and the maximum is V_CC. The
terminology of R_H and R_L references the relative posi-
tion of the terminal in relation to wiper movement
direction selected by the U/D input per potentiometer.
Up/Down (U/D)
The U/D input controls the direction of a single potenti-
ometer’s wiper movement and whether the counter is
incremented or decremented.
Increment (INC)
The INC input is negative-edge triggered. Toggling
INC will move the wiper and either increment or decre-
ment the corresponding potentiometer’s counter in the
direction indicated by the logic level on the corre-
sponding potentiometer’s U/D input.
Chip Select (CS)
A potentiometer is selected when the corresponding CS
input is LOW. Its current counter value is stored in non-
volatile memory when the corresponding CS is returned
HIGH while the corresponding INC input is also HIGH.
After the store operation is complete the affected poten-
tiometer will be placed in the low power standby mode
until the potentiometer is selected once again.
PRINCIPLES OF OPERATION
There are multiple sections for each potentiometer in
the X93254: an input control, a counter and decode
section; the nonvolatile memory; and a resistor array.
Each input control section operates just like an
up/down counter. The output of this counter is
decoded to turn on a single electronic switch connect-
ing 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 com-
prised 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 posi-
tion stored will be maintained in the nonvolatile mem-
ory 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 wiper along the resistor array. With CS set LOW
the 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 five 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 mem-
ory whenever each CS transitions HIGH while the INC
input is also HIGH. In order to avoid an accidental store
during power-up, each CS must go HIGH with V_CC dur-
ing 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 X93254, move any wiper
and deselect the device without having to store the lat-
est wiper position in nonvolatile memory. After the wiper
movement is performed as described above 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 pref-
erence, system parameter changes due to tempera-
ture drift, or other system trim requirements.
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FN8186.0
March 1, 2005