X9C303_07 Datasheet, PDF (3/10 Pages) Intersil Corporation – Logarithmic Digitally Controlled Potentiometer

X9C303
Potentiometer Relationships
V_H
(V_S) _R99
S100
S99
R98
S98
V_W
S3
R2
S2
R1
S1
V_L
Gi
=
20 L o g ^{R-----1-----+-----R----2-----+-----.----.---.---+-----R-----i}
RTOTAL
=
V-----W----
VS
(
VL
=
0V)
R1 + R2 + . . . + R99 = RTOTAL
(Refer Test Circuit 1)
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 described above; 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.
Mode Selection
CS INC U/D
L
H Wiper Up
MODE
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)
3
FN8223.1
January 24, 2007