ADC0831 Parallax Inc, ADC0831 Datasheet - Page 12

• Manufacturer Part Number: ADC0831
• Description: ADC (A/D Converters) 8-bit ADC DIP ADC0831
• Manufacturer: Parallax Inc

Specifications of ADC0831

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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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 in-
put 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 “−” in-
put the converter responds with an all zeros output code.
A unique input multiplexing scheme has been utilized to pro-
vide 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 con-
ditioning required in transducer-based data acquisition sys-
tems 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.
ADC0831
ADC0832
ADC0834
ADC0838
Number
Part
TABLE 1. Multiplexer/Package Options
Single-Ended
Number of Analog Channels
1
2
4
8
12
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 se-
lected as a different pair but channel 0 or 1 cannot act differ-
entially 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 il-
lustrated by the MUX addressing codes shown in the follow-
ing 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.
1
1
2
4
Package Pins
Number of
14
20
8
8