3
FN8178.3
July 24, 2014
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Typical Attenuation Characteristics (dB)
Principles of Operation
There are three sections of the X9314: 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
31 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 INC
, U/D and CS inputs control the movement of the
wiper along the resistor array. With CS
set LOW the X9314
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 five bit counter. The output of this counter is
decoded to select one of thirty-two wiper positions along the
resistive array.
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 value of the counter is stored in nonvolatile memory
whenever CS
transistions HIGH while the INC input is also
HIGH.
When the X9314 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.
Operation Notes
The system may select the X9314, 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 keep the INC
LOW while taking
CS
HIGH. The new wiper position would be maintained until
changed by the system or until a power-up/down 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 X9314 and then
move the wiper up and down until the proper trim is attained.
t
IW
/R
TOTAL
The electronic switches on the X9314 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.
Power-up and Down Requirement
The are no restrictions on the sequencing of V
CC
and the
voltages applied to the potentiometer pins during power-up
or power-down conditions. During power-up, the data sheet
parameters for the DCP do not fully apply until 1 millisecond
after V
CC
reaches its final value. The V
CC
ramp rate spec is
always in effect.
TAP POSITION
0
48
12
1620242831
-20
-40
-43.5
0
-60
ATTENUATION (dB)
X9314
