CAT5127_0708 datasheet(3/13 Pages) CATALYST

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CAT5127, CAT5129

Doc. No. MD-2127 Rev. C

Characteristics subject to change without notice

DEVICE OPERATION

The CAT5127 operates like a digitally controlled

variable resistor with RH and RL equivalent to the high

and low terminals. There are 32 available tap posi-

tions including the resistor end points, RH and RL.

There are 31 resistor elements connected in series

between the RH and RL terminals.

The CAT5129 operates like a digitally controlled

variable resistor with RH equivalent to the high

terminal. There are 32 available tap positions

including the resistor end points, RH and GND. There

are 31 resistor elements connected in series between

the RH and GND terminals.

Operation is controlled by three inputs, INC

¯¯¯, U/D

¯ and

¯¯ . 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

¯¯¯

¯¯

U/D

Operation

High to Low

Low

High

Wiper toward H

High to Low

Low

Wiper toward L/GND

High

Low to High

Store Wiper Position

Low

Low to High

No Store, Return to Standby

High

Standby

Variable Resistor Equivalent Circuit

RL/GND

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