9

FN6176.0

July 17, 2006

Pin Descriptions

Potentiometers Pins

RHi and RLi (i = 0, 1)

The high (RHi) and low (RLi) terminals of the ISL22326 are

equivalent to the fixed terminals of a mechanical

potentiometer. RHi and RLi are referenced to the relative

position of the wiper and not the voltage potential on the

terminals. With WRi set to 127 decimal, the wiper will be

closest to RHi, and with the WRi set to 0, the wiper is closest

to RLi.

RWi (i = 0,1)

RWi 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 WRi register.

SHDN

The SHDN pin forces the resistor to end-to-end open circuit

condition on RHi and shorts RWi to RLi. When SHDN is

returned to logic high, the previous latch settings put RWi at

the same resistance setting prior to shutdown. This pin is

still available in shutdown mode and all registers are

accessible. This pin must remain HIGH for normal operation.

Bus Interface Pins

Serial Data Input/Output (SDA)

interface. It receives device address, operation code, wiper

rising edge of the serial clock SCL, and it shifts out data after

each falling edge of the serial clock.

SDA requires an external pull-up resistor, since it is an open

drain input/output.

Serial Clock (SCL)

requires an external pull-up resistor, since it is an open drain

input.

Device Address (A2 - A0)

The address inputs are used to set the least significant 3 bits

address serial data stream must match with the Address

input pins in order to initiate communication with the

ISL22326. A maximum of 8 ISL22326 devices may occupy

Principles of Operation

The ISL22326 is an integrated circuit incorporating two

DCPs with their associated registers, non-volatile memory

between a host and the potentiometers and memory. The

resistor arrays are comprised of 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 electronic switches on the device operate in a “make

before break” mode when the wiper changes tap positions.

FIGURE 13. MIDSCALE GLITCH, CODE 3Fh TO 40h

FIGURE 14. LARGE SIGNAL SETTLING TIME

Wiper Mid Point Movement

from 3Fh to 40h

RL

RW

RH

FIGURE 15. DCP CONNECTION IN SHUTDOWN MODE

ISL22326