CAT5111
http://onsemi.com
3
Pin Description
INC: Increment Control Input
The INC
input (on the falling edge) moves the wiper in the
up or down direction determined by the condition of the U/D
input.
U/D
: Up/Down Control Input
The U/D
input controls the direction of the wiper movement.
When in a high state and CS
is low, any high-to-low
transition on INC
will cause the wiper to move one
increment toward the R
H
terminal. When in a low state and
CS
is low, any high-to-low transition on INC will cause the
wiper to move one increment towards the R
L
terminal.
R
H
: High End Potentiometer Terminal
R
H
is the high end terminal of the potentiometer. It is not
required that this terminal be connected to a potential greater
than the R
L
terminal. Voltage applied to the R
H
terminal
cannot exceed the supply voltage, V
CC
or go below ground,
GND.
R
WB
: Wiper Potentiometer Terminal (Buffered)
R
WB
is the buffered wiper terminal of the potentiometer. Its
position on the resistor array is controlled by the control
inputs, INC
, U/D and CS.
R
L
: Low End Potentiometer Terminal
R
L
is the low end terminal of the potentiometer. It is not
required that this terminal be connected to a potential less
than the R
H
terminal. Voltage applied to the R
L
terminal
cannot exceed the supply voltage, V
CC
or go below ground,
GND. R
L
and R
H
are electrically interchangeable.
CS
: Chip Select
The chip select input is used to activate the control input of
the CAT5111 and is active low. When in a high state, activity
on the INC
and U/D inputs will not affect or change the
position of the wiper.
Device Operation
The CAT5111 operates like a digitally controlled
potentiometer with R
H
and R
L
equivalent to the high and low
terminals and R
WB
equivalent to the mechanical
potentiometer’s wiper. There are 100 available tap positions
including the resistor end points, R
H
and R
L
. There are 99
resistor elements connected in series between the R
H
and R
L
terminals. The wiper terminal is connected to one of the 100
taps and controlled by three inputs, INC
, U/D and CS. These
inputs control a seven-bit up/down counter whose output is
decoded to select the wiper position. The selected wiper
position can be stored in nonvolatile memory using the INC
and CS inputs.
With CS
set LOW the CAT5111 is selected and will
respond to the U/D
and INC inputs. HIGH to LOW
transitions on INC
will increment or decrement the wiper
(depending on the state of the U/D
input and seven−bit
counter). The wiper, when at either fixed terminal, acts like
its mechanical equivalent and does not move beyond the last
position. The value of the counter is stored in nonvolatile
memory whenever CS
transitions HIGH while the INC input
is also HIGH. When the CAT5111 is powered-down, the last
stored wiper counter position is maintained in the
nonvolatile memory. When power is restored, the contents
of the memory are recalled and the counter is set to the value
stored.
With INC
set low, the CAT5111 may be de-selected and
powered down without storing the current wiper position in
nonvolatile memory. This allows the system to always
power up to a preset value stored in nonvolatile memory.
