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ADC08131 Просмотр технического описания (PDF) - National ->Texas Instruments

Номер в каталогеADC08131 National-Semiconductor
National ->Texas Instruments National-Semiconductor
Компоненты Описание8-Bit High-Speed Serial I/O A/D Converters with Multiplexer Options, Voltage Reference, and Track/Hold Function
ADC08131 Datasheet PDF : 22 Pages
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Functional Description
MULTIPLEXER ADDRESSING
The design of these converters utilizes a comparator struc-
ture with built-in sample-and-hold which provides for a differ-
ential analog input to be converted by a successiveapproxi-
mation 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 indicates which
line the converter expects to be the most positive. If the
assigned “+” input voltage is less than the “−” input voltage
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 pseudo-differential (which will
convert the difference between the voltage at any analog
input and a common terminal) operation. 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.
Differential inputs are restricted to adjacent channel pairs.
For example, channel 0 and channel 1 may be selected as a
differential pair but channel 0 or 1 cannot act differentially
with any other channel. In addition to selecting differential
mode the polarity 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 ADC08131 contains only one differential input
channel with a fixed polarity assignment, it does not require
addressing.
The common input line (COM) on the ADC08138 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 applica-
tions where the analog circuity 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
ADC08131
ADC08134
ADC08138
Number of Analog Channels
Single-Ended Differential
1
1
4
2
8
4
Number of
Package
Pins
8
14
20
TABLE 2. MUX Addressing: ADC08138
Single-Ended MUX Mode
MUX Address
Analog Single-Ended Channel #
START
SGL/
ODD/
SELECT
0
1
2
3
4
5
6
7
COM
DIF
SIGN
1
0
1
1
0
0
0
+
1
1
0
0
1
+
1
1
0
1
0
+
1
1
0
1
1
+
1
1
1
0
0
+
1
1
1
0
1
+
1
1
1
1
0
+
1
1
1
1
1
+
TABLE 3. MUX Addressing: ADC08138
Differential MUX Mode
MUX Address
START
SGL/
ODD/
DIF
SIGN
1
0
0
1
0
0
1
0
0
1
0
0
1
0
1
1
0
1
1
0
1
SELECT
1
0
0
0
0
1
1
0
1
1
0
0
0
1
1
0
0
0
1
+
+
Analog Differential Channel-Pair #
1
2
2
3
4
5
+
+
+
+
3
6
7
+
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