ADC0831-N, ADC0832-N, ADC0834-N, ADC0838-N

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SNAS531B – AUGUST 1999 – REVISED MARCH 2013

Functional Description

Multiplexer Addressing

The design of these converters utilizes a sample-data comparator structure which provides for a differential

analog input to be converted by a successive approximation routine.

The actual voltage converted is always the difference between an assigned “+” input terminal and a “

−” input

terminal. The polarity of each input terminal of the pair being converted 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 channel 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 following

tables for the various product options.

The MUX address is shifted into the converter via the DI line. Because the ADC0831-N contains only one

differential input channel with a fixed polarity assignment, it does not require addressing.

The common input line on the ADC0838-N 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 Single-Ended MUX Mode

Number of Analog Channels

Part Number

Number of Package Pins

Single-Ended

Differential

ADC0831-N

1

1

8

ADC0832-N

2

1

8

ADC0834-N

4

2

14

ADC0838-N

8

4

20

Table 2. MUX Addressing: ADC0838-N Single-Ended MUX Mode

MUX Address

Analog Single-Ended Channel #

SGL/

ODD/

SELECT

0

1

2

3

4

5

6

7

COM

DIF

SIGN

1

0

1

0

0

0

+

−

1

0

0

1

+

−

1

0

1

0

+

−

1

0

1

1

+

−

1

1

0

0

+

−

1

1

0

1

+

−

1

1

1

0

+

−

1

1

1

1

+

−

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Product Folder Links: ADC0831-N ADC0832-N ADC0834-N ADC0838-N