the data output on DO is not possible since an end of con-

version signal from the AD is not available and the actual

conversion time is not known With CS low during the con-

ed Once the conversion is through DO will transmit the

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

12 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 AD in a

digital testing mode In this mode the analog inputs CH0

thru CH4 become digital outputs for our use in production

testing

20 ANALOG INPUT

21 THE INPUT SAMPLE AND HOLD

The ADC0819’s samplehold 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 msec after the

start of the conversion process An acquisition window of

capacitance to settle to the analog input voltage Any

change in the analog voltage before or after the acquisition

window will not effect the AD conversion result

In the most simple case the ladder’s acquisition time is de-

total ladder capacitance (90pf) These values yield an acqui-

sition time of about 2 msec for a full scale reading There-

fore the analog input must be stable for at least 2 msec

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 AD The hold

step and gain error samplehold specs are taken into ac-

count in the ADC0819’s total unadjusted error while the

hold settling time is included in the AD’s max conversion

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

TLH9287 – 18

9