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參數(shù)資料
| 型號(hào)： | LF13508MX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 多路復(fù)用及模擬開(kāi)關(guān) |
| 英文描述： | 8-CHANNEL, SGL ENDED MULTIPLEXER, PDSO16 |
| 封裝： | 0.150 INCH, PLASTIC, SOP-16 |
| 文件頁(yè)數(shù)： | 14/16頁(yè) |
| 文件大小： | 334K |
| 代理商： | LF13508MX |
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Typical Applications
DATA ACQUISITION SYSTEM
A SIMPLIFIED SYSTEM DISCUSSION
Analog multiplexers (MUX) are usually used for multi-chan-
nel Data Acquisition Units (DAU)
Figure 5 shows a system
in which 8 different analog inputs are sampled and convert-
ed into digital words for further processing The sample and
hold circuit is optional depending on input speed require-
ments and on AD converter speed
Parameters characterizing the system are
System Channels
The number of multiplexer channels
Accuracy
The conversion accuracy of each individual sam-
ple with the system operating at the throughput rate
Speed or Throughput Rate
Number of samplessecond
channel the system can handle
For a discussion on system structure addressing mode and
processor interfacing see application note AN-159
A ACCURACY CONSIDERATIONS
1 Multiplexer’s Influence on System Accuracy
(Figure 6)
a The error (E) caused by the finite ‘‘ON’’ resist-
ance RON of the multiplexing switches is given
by
E(%) e
100
1 a RIN (RON a RS a DRON)
where
RIN e following stage input impedance
D
RON e ‘‘ON’’ resistance modulation which is
negligible for JFET switches like the LF11508
Example Let RON e 450 X DRON e 0 RS e 0 TA
e
25 C and allowable E e 001% which is equivalent
to 12 LSB in a 12-bit system
RIN
min
e
RON(100 b E)
E
e
45 MX
Note that if temperature effects are included some
gain (or full scale) drift will occur but effects on linearity
are small
b Multiplexer settling time (ts)
ts(ON) is the time required for the MUX output to
settle within a predetermined accuracy
as
shown in Table I
CS (Figure 6) MUX output capacitance a fol-
lowing stage input capacitance a any stray ca-
pacitance at this node
TABLE I
ERROR %
BITS
ts(ON)
TO 12 LSB
02
8
62t
005
10
76t
001
12
9t
00008
16
118t
t e CS (RON a RS)
ll RIN
ts(OFF) is the time it takes to discharge CS within
a tolerable error The ‘‘OFF’’ settling time should
be taken into account for bipolar inputs where its
effects will appear as a worse case of doubling
of the ts(ON)
2 Sample and Hold Influence on System Accuracy
The sample and hold if used also introduces errors into
the system accuracy due to
Offset voltage of sample and hold
Droop rate in the Hold mode
TA Aperture time or time delay between the time of a
digital Hold command and the actual Hold occurance
Taq Acquisition time or time it takes to acquire an
analog input and settle within a predetermined error
band
Hold step Error created during the Sample to Hold
mode caused by an undesirable charge injected into
the Hold capacitor Ch
For more details on sample and hold errors see the
LF198LF298LF398 data sheet
3 AD Converter Influence on System Accuracy
The ‘‘a(chǎn)ccuracy’’ of the AD converter is the best possible
system accuracy In most data acquisition systems the
AD converter is the most expensive single component
so its error will often dominate system error Care should
be taken that MUX SH and input source errors do not
exceed system error requirements when
added to AD
errors For instance if an 8-bit accuracy system is desired
and an 8-bit AD converter is used the accuracy of the
MUX and SH should be far better than 8 bits
For details on AD converter specifications see AN-156
TLH5668 – 13
FIGURE 5 Random-Addressed Multiplexed DAU
FIGURE 6 8-Channel MUX
7
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LF13508N | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:8-Channel Analog Multiplexer |
| LF13508N/B+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:8-Channel Analog Multiplexer |
| LF13509 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:8-Channel Analog Multiplexer |
| LF13509D | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| LF13509M | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:8-Channel Analog Multiplexer |
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