Principles of Operation
There are three sections of the X9116: the input control,
counter and decode section; the nonvolatile memory; and the
resistor array. The input control 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. The resistor array is comprised of
15 individual resistors connected in series. At either end of the
array and between each resistor is an electronic switch that
transfers the potential at that point to the wiper pin.
The 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.
The electronic switches on the device operate in a “make
before break” mode when the wiper changes tap positions. If
the wiper is moved several positions, multiple taps are
connected to the wiper for tIW (INC to VW change). The
RTOTAL value for the device can temporarily be reduced 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. When
power is restored, the contents of the memory are recalled and
the 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 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 four bit counter.
The output of this counter is decoded to select one of 16 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
The system may select the X9116, 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 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 recalls the
previously stored data.
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, etc.
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.
CS INC U/D
Store Wiper Position
No Store, Return to Standby
from Low to
from High to
from Low to
from High to
FN8160 Rev 3.00
February 3, 2011
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