ADC0832CIWM datasheet(13/33 Pages) NSC

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Functional Description

1.0 multiplexer Addressing

The design of these converters utilizes a sample-data com-

parator structure which provides for a differential analog

input to be converted by a successive approximation routine.

The actual voltage converted is always the difference be-

tween an assigned “+” input terminal and a “−” input terminal.

The polarity of each input terminal of the pair being con-

verted indicates which line the converter expects to be the

most positive. If the assigned “+” input is less than the “−”

input the converter responds with an all zeros output code.

A unique input multiplexing scheme has been utilized to

provide multiple analog channels with software-configurable

single-ended, differential, or a new pseudo-differential option

which will convert the difference between the voltage at any

analog input and a common terminal. The analog signal

conditioning required in transducer-based data acquisition

systems is significantly simplified with this type of input

flexibility. One converter package can now handle ground

referenced inputs and true differential inputs as well as

signals with some arbitrary reference voltage.

A particular input configuration is assigned during the MUX

addressing sequence, prior to the start of a conversion. The

MUX address selects which of the analog inputs are to be

enabled and whether this input is single-ended or differential.

In the differential case, it also assigns the polarity of the

channels. Differential inputs are restricted to adjacent chan-

nel pairs. For example channel 0 and channel 1 may be

selected as a different pair but channel 0 or 1 cannot act

differentially with any other channel. In addition to selecting

differential mode the sign may also be selected. Channel 0

may be selected as the positive input and channel 1 as the

negative input or vice versa. This programmability is best

illustrated by the MUX addressing codes shown in the fol-

lowing tables for the various product options.

The MUX address is shifted into the converter via the DI line.

Because the ADC0831 contains only one differential input

channel with a fixed polarity assignment, it does not require

addressing.

The common input line on the ADC0838 can be used as a

pseudo-differential input. In this mode, the voltage on this pin

is treated as the “−” input for any of the other input channels.

This voltage does not have to be analog ground; it can be

any reference potential which is common to all of the inputs.

This feature is most useful in single-supply application where

the analog circuitry may be biased up to a potential other

than ground and the output signals are all referred to this

potential.

TABLE 1. Multiplexer/Package Options

Part

Number of Analog Channels

Number of

Number

Single-Ended

Differential

Package Pins

ADC0831

ADC0832

ADC0834

ADC0838

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