參數(shù)資料
型號: ADC08238
廠商: National Semiconductor Corporation
英文描述: 16 A SPDT MINIATURE POWER RELAY
中文描述: 8位2毫秒串行I /辦公自動化/ D的多路復用器,參考轉換器,和采樣/保持
文件頁數(shù): 13/24頁
文件大小: 419K
代理商: ADC08238
Functional Description
1.0 MULTIPLEXER ADDRESSING
The design of these converters utilizes a comparator struc-
ture with built-in sample-and-hold which provides for a dif-
ferential analog input to be converted by a successive-
approximation routine.
The actual voltage converted is always the difference be-
tween an assigned ‘‘
a
’’ input terminal and a ‘‘
b
’’ input ter-
minal. The polarity of each input terminal of the pair indi-
cates which line the converter expects to be the most posi-
tive. If the assigned ‘‘
a
’’ input voltage is less than the ‘‘
b
’’
input voltage the converter responds with an all zeros out-
put code.
A unique input multiplexing scheme has been utilized to pro-
vide 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 flexi-
bility. One converter package can now handle ground refer-
enced 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 differen-
tial. Differential inputs are restricted to adjacent channel
pairs. For example, channel 0 and channel 1 may be select-
ed 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 ADC08231 contains only one differential
input channel with a fixed polarity assignment, it does not
require addressing.
The common input line (COM) on the ADC08238 can be
used as a pseudo-differential input. In this mode the voltage
on this pin is treated as the ‘‘
b
’’ 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-sup-
ply applications 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 I. Multiplexer/Package Options
Part
Number
Number of Analog Channels
Number of
Package Pins
Single-Ended
Differential
ADC08231
1
1
8
ADC08234
4
2
14
ADC08238
8
4
20
TABLE II. MUX Addressing: ADC08238
Single-Ended MUX Mode
MUX Address
Analog Single-Ended Channel
Y
START
SGL/
DIF
ODD/
SIGN
SELECT
0
1
2
3
4
5
6
7
COM
1
0
1
1
0
0
0
a
b
1
1
0
0
1
a
b
1
1
0
1
0
a
b
1
1
0
1
1
a
b
1
1
1
0
0
a
b
1
1
1
0
1
a
b
1
1
1
1
0
a
b
1
1
1
1
1
a
b
13
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相關代理商/技術參數(shù)
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