3FN8223.2
January 30, 2009
Potentiometer Relationships
Principles of Operation
There are three sections of the X9C303: the input co ntrol,
counter and decode section; the nonvolatile memory; and the
resistor array. The input control se ction operates just l ike an
up/down counter. The output of thi s counter is decoded to turn
on a single electronic switch connecting a point on the resistor
array to the wiper output. Under the proper con ditions, the
contents of the counter can be sto red in nonvolatile memory
and retained fo r future use. The resisto r array is comprised of
99 individual resistors connected in series. At ei ther end of the
array and between each resistor is an electronic sw itch that
transfers the potential at that point to the wipe r.
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 aroun d when
clocked to either extreme.
The electronic switches on the device operate in a “ma ke
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 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 input s 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 input s.
HIGH to LOW transitions on INC will increment or decrement
(depending on the st ate of th e U/D in put) a seven-bit counter.
The output of this counter is decoded to select on e of
one-hundred wiper positions along the re sistive arra y.
The value of the counter is stored in no nvolatile 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
VHHigh Terminal (Potentiometer)
VWWiper Terminal (Potentiometer)
VLLow Terminal (Potentiometer)
VSS Ground
VCC Supply Voltage
U/D Up/Down Control Input
INC Increment Control Input
CS Chip Select Control Input
NC No Connection
VL
VH
(VS)R99
R98
R2
R1
S100
S99
S98
S3
S2
S1
VW
Gi20LogR1R2. . . Ri
+++
RTOTAL
------------------------------------------------- VW
VS
--------- V L0V=()==
R1R2. . . R99
+++ R
TOTAL
=
(REFER TEST CIRC UIT 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