参数资料
型号: ADC0811BCN
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: ADC
英文描述: 8-Bit Serial I/O A/D Converter With 11-Channel Multiplexer
中文描述: 11-CH 8-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDIP20
封装: 0.300 INCH, PLASTIC, DIP-20
文件页数: 10/14页
文件大小: 323K
代理商: ADC0811BCN
Functional Description
(Continued)
at least 64
w
2
clocks to insure 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 (64
w
2
max) DO will go low after the eighth
falling edge of S
CLK
and remain low until the conversion is
completed. 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 four 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 twelve (11XX) as this puts the A/D in a digital
testing mode. In this mode the analog inputs CH0 thru CH3
become digital outputs, for our use in production testing.
2.0 ANALOG INPUT
2.1 THE INPUT SAMPLE AND HOLD
The ADC0811’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
4t
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 ADC0811’s total unadjusted error, while the
hold settling time is included in the A/D’s max conversion
time of 64
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
ADC0811-INS8048 INTERFACE
TL/H/5587–21
10
相关PDF资料
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