3
FN8223.2
January 30, 2009
Potentiometer Relationships
Principles of Operation
There are three sections of the X9C303: 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
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 memory
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 latest wiper
position in nonvolatile memory. The wiper movement is
performed as previously described ; once the new position is
reached, the system would the keep INC
LOW while taking
CS
HIGH. The new wiper position 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.
Pin Names
SYMBOL DESCRIPTION
V
H
High Terminal (Potentiometer)
V
W
Wiper Terminal (Potentiometer)
V
L
Low Terminal (Potentiometer)
V
SS
Ground
V
CC
Supply Voltage
U/D
Up/Down Control Input
INC Increment Control Input
CS Chip Select Control Input
NC No Connection
V
L
V
H
(V
S
)
R99
R98
R2
R1
S100
S99
S98
S3
S2
S1
V
W
G
i
20Log
R
1
R
2
. . . R
i
+++
R
TOTAL
-------------------------------------------------
V
W
V
S
--------- V
L
0V=()==
R
1
R
2
. . . R
99
+++ R
TOTAL
=
(REFER TEST CIRCUIT 1)
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)
X9C303
