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FN6176.3

September 9, 2015

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

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.

When the device is powered down, the last value stored in

IVRi will be maintained in the non-volatile memory. When

power is restored, the contents of the IVRi are recalled and

loaded into the corresponding WRi to set the wipers to the

initial value.

DCP Description

Each DCP is implemented with a combination of resistor

elements and CMOS switches. The physical ends of each

DCP are equivalent to the fixed terminals of a mechanical

potentiometer (RH and RL pins). The RW pin of each DCP is

connected to intermediate nodes, and is equivalent to the

wiper terminal of a mechanical potentiometer. The position

of the wiper terminal within the DCP is controlled by volatile

Wiper Register (WR). Each DCP has its own WR. When the

WR of a DCP contains all zeroes (WR[6:0]= 00h), its wiper

terminal (RW) is closest to its “Low” terminal (RL). When the

WR register of a DCP contains all ones (WR[6:0] = 7Fh), its

wiper terminal (RW) is closest to its “High” terminal (RH). As

the value of the WR increases from all zeroes (0) to all ones

(127 decimal), the wiper moves monotonically from the

position closest to RL to the closest to RH. At the same time,

the resistance between RW and RL increases monotonically,

while the resistance between RH and RW decreases

monotonically.

While the ISL22326 is being powered up, all WRs are reset

to 40h (64 decimal), which locates RW roughly at the center

between RL and RH. After the power supply voltage

becomes large enough for reliable non-volatile memory

reading, all WRs will be reload with the value stored in

corresponding non-volatile Initial Value Registers (IVRs).

serial interface as described in the following sections. The

access the WR of DCP0 or DCP1 respectively.

Memory Description

The ISL22326 contains seven non-volatile and three volatile

8-bit registers. Memory map of ISL22326 is on Table 1. The

two non-volatile registers (IVRi) at address 0 and 1, contain

initial wiper value and volatile registers (WRi) contain current

wiper position. In addition, five non-volatile General Purpose

registers from address 2 to address 6 are available.

RL

RW

RH

FIGURE 15. DCP CONNECTION IN SHUTDOWN MODE

ISL22326