CAT5127, CAT5129
DEVICE OPERATION
The CAT5127 operates like a digitally controlled
variable resistor with R
H
and R
L
equivalent to the high
and low terminals. There are 32 available tap posi-
tions including the resistor end points, R
H
and R
L
.
There are 31 resistor elements connected in series
between the R
H
and R
L
terminals.
The CAT5129 operates like a digitally controlled
variable resistor with R
H
equivalent to the high
terminal. There are 32 available tap positions
including the resistor end points, R
H
and GND. There
are 31 resistor elements connected in series between
the R
H
and GND terminals.
¯¯¯
¯
Operation is controlled by three inputs, INC, U/D and
¯¯
CS. These inputs control a five-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 device is selected and will
¯
¯¯¯
respond to the U/D and INC inputs. HIGH to LOW
¯¯¯
transitions on INC wil increment or decrement the
¯
wiper (depending on the state of the U/D input and
five-bit counter). The wiper, when at either end
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 device 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 device 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.
OPERATION MODES
¯¯¯
INC
High to Low
High to Low
High
Low
X
¯¯
CS
Low
Low
Low to High
Low to High
High
¯
U/D
High
Low
X
X
X
Operation
Wiper toward H
Wiper toward L/GND
Store Wiper Position
No Store, Return to Standby
Standby
R
H
C
H
C
L
R
L
/GND
Variable Resistor Equivalent Circuit
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3
Doc. No. MD-2127 Rev. C
CATALYST [ CATALYST SEMICONDUCTOR ]
