參數(shù)資料
型號(hào): ADC0819BCN
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: ADC
英文描述: 8-Bit Serial I/O A/D Converter with 19-Channel Multiplexer
中文描述: 19-CH 8-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDIP28
封裝: 0.600 INCH, PLASTIC, DIP-28
文件頁數(shù): 9/12頁
文件大?。?/td> 279K
代理商: ADC0819BCN
Functional Description
(Continued)
at least 32
w
2
clocks to ensure that the A/D has completed
its conversion. If S
CLK
is enabled sooner, synchronizing to
the data output on DO is not possible since an end of con-
version signal from the A/D is not available and the actual
conversion time is not known. With CS low during the con-
version time (32
w
2
max) DO will go high or low after the
eighth falling edge of S
CLK
until the conversion is complet-
ed. Once the conversion is through DO will transmit the
MSB. The rest of the data will be shifted out once S
CLK
is
enabled as discussed previously.
If CS goes high during the conversion sequence DO is tri-
stated, and the result is not affected so long as CS remains
high until the end of the conversion.
1.2 MULTIPLEXER ADDRESSING
The five bit mux address is shifted, MSB first, into DI. Input
data corresponds to the channel selected as shown in table
1. Care should be taken not to send an address greater than
or equal to twenty four (11XXX) as this puts the A/D in a
digital testing mode. In this mode the analog inputs CH0
thru CH4 become digital outputs, for our use in production
testing.
2.0 ANALOG INPUT
2.1 THE INPUT SAMPLE AND HOLD
The ADC0819’s sample/hold capacitor is implemented in its
capacitive ladder structure. After the channel address is re-
ceived, the ladder is switched to sample the proper analog
input. This sampling mode is maintained for 1
m
sec after the
eighth S
CLK
falling edge. The hold mode is initiated with the
start of the conversion process. An acquisition window of
3t
SCLK
a
1
m
sec is therefore available to allow the ladder
capacitance to settle to the analog input voltage. Any
change in the analog voltage before or after the acquisition
window will not effect the A/D conversion result.
In the most simple case, the ladder’s acquisition time is de-
termined by the R
on
(3K) of the multiplexer switches and the
total ladder capacitance (90pf). These values yield an acqui-
sition time of about 2
m
sec for a full scale reading. There-
fore the analog input must be stable for at least 2
m
sec
before and 1
m
sec after the eighth S
CLK
falling edge to
ensure a proper conversion. External input source resist-
ance and capacitance will lengthen the acquisition time and
should be accounted for.
Other conventional sample and hold error specifications are
included in the error and timing specs of the A/D. The hold
step and gain error sample/hold specs are taken into ac-
count in the ADC0819’s total unadjusted error, while the
hold settling time is included in the A/D’s max conversion
time of 32
w
2
clock periods. The hold droop rate can be
thought of as being zero since an unlimited amount of time
can pass between a conversion and the reading of data.
However, once the data is read it is lost and another conver-
sion is started.
Typical Applications
ADC0819-INS8048 INTERFACE
TL/H/9287–18
9
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相關(guān)代理商/技術(shù)參數(shù)
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ADC0819CCV 制造商:Texas Instruments 功能描述: