ADG2108BCPZ-R2 datasheet(18/28 Pages) AD

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ADG2108

Rev. 0 | Page 18 of 28

THEORY OF OPERATION

The ADG2108 is an analog cross point switch with an array size

of 8 × 10. The 10 rows are referred to as the X input/output lines,

and the eight columns are referred to as the Y input/output

lines. The device is fully flexible in that it connects any X line or

number of X lines with any Y line when turned on. Similarly, it

connects any X line with any number of Y lines when turned on.

Control of the ADG2108 is carried out via an I2C interface.

The device can be operated from single supplies of up to 13.2 V

or from dual ±5 V supplies. The ADG2108 has many attractive

features, such as the ability to reset all the switches, the ability to

update many switches at the same time, and the option of reading

back the status of any switch. All of these features are described

in more detail here in the Theory of Operation section.

RESET/POWER-ON RESET

The ADG2108 offers the ability to reset all of the 80 switches to

the off state. This is done through the RESET pin. When the

RESET pin is low, all switches are open (off), and appropriate

registers are cleared. Note that the ADG2108 also has a power-

on reset block. This ensures that all switches are in the off

condition at power-up of the device. In addition, all internal

registers are filled with 0s and remain so until a valid write to

the ADG2108 takes place.

LOAD SWITCH (LDSW)

LDSW is an active high command that allows a number of

switches to be simultaneously updated. This is useful in

applications where it is important to have synchronous

transmission of signals. There are two LDSW modes: the

transparent mode and the latched mode.

Transparent Mode

In this mode, the switch position changes after the new word is

written into the input shift register. LDSW is set to 1.

Latched Mode

In this mode, the switch positions are not updated at the same

time that the input registers are written to. This is achieved by

setting LDSW to 0 for each word (apart from the last word)

written to the device. Then, setting LDSW to 1 for the last word

allows all of the switches in that sequence to be simultaneously

updated.

READBACK

Readback of the switch array conditions is also offered when in

standard mode and fast mode. Readback enables the user to

check the status of the switches of the ADG2108. This is very

useful when debugging a system.

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