X9C303 Datasheet, PDF (3/10 Pages) Xicor Inc. – Digitally Controlled Potentiometer (XDCP)

X9C303
PRINCIPLES OF OPERATION
There are three sections of the X9C303: the input con-
trol, counter and decode section; the nonvolatile mem-
ory; 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 com-
prised of 99 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.
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 t_IW (INC to
V_W change). The R_TOTAL 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 counter
position stored will be maintained in the nonvolatile
memory. When power is restored, the contents of the
memory are recalled and the counter is reset 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 seven-bit counter. The output of this
counter is decoded to select one of one-hundred wiper
positions along the resistive array.
The value of the counter is stored in nonvolatile mem-
ory whenever CS transitions HIGH while the INC input
is also HIGH.
The system may select the X9C303, move the wiper,
and deselect the device without having to store the lat-
est wiper position in nonvolatile memory. The wiper
movement is performed as described above; once the
new position is reached, the system would the keep
INC LOW while taking CS HIGH. The new wiper posi-
tion would be maintained until changed by the system
or until a power-down/up cycle recalled the previously
stored data.
This would allow 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.
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
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
3
FN8223.0
March 11, 2005