RH/VH and RL/VL
The high (RH/VH) and low (RL/VL) terminals of the X9015 are
equivalent to the fixed terminals of a mechanical
potentiometer. The minimum voltage is VSS and the
maximum is VCC. The terminology of RL/VL and RH/VH
references the relative position of the terminal in relation to
wiper movement direction selected by the U/D input, and not
the voltage potential on the terminal.
RW/Vw is the wiper terminal and is equivalent to the movable
terminal of a mechanical potentiometer. The position of the
wiper within the array is determined by the control inputs.
The wiper terminal series resistance is typically 200Ω at
VCC=5V. At power up the wiper position is at Tap #15.
The U/D input controls the direction of the wiper movement
and whether the tap position is incremented or decremented.
The INC input is negative-edge triggered. Toggling INC will
move the wiper and either increment or decrement the
counter in the direction indicated by the logic level on the U/D
Chip Select (CS)
The device is selected when the CS input is LOW. When CS
is returned HIGH while the INC input is also HIGH the X9015
will be placed in the low power standby mode until the device
is selected once again.
Up/Down control input
Increment control input
Chip select control input
Principles Of Operation
There are two sections of the X9015: the input control,
counter and decode section; 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. The resistor array is comprised of 31 individual
resistors connected in series.
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 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 wiper position is lost.
When power is restored, the wiper is set to Tap #15.
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 five bit counter.
The output of this counter is decoded to select one of thirty
two wiper positions along the resistive array.
The system may select the X9015, move the wiper and
deselect the device. The new wiper position will be maintained
until changed by the system or until a power-up/down cycle.
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.
CS INC U/D
Wiper Up (not recommended)
Wiper Down (not recommend-
August 31, 2006