AD7745: Capacitance Application

Document created by analog-archivist Employee on Feb 23, 2016
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1.:What is the difference between the AD7745 and the AD7747? Is it only the
different resolution and accuracy and the input range?
2.:What is the difference between the models for the AD7746: ARUZ / REEL / REEL
7 ?
3.:If the resolution of the AD7746 is stated as down to 4aF, can I really
measure a change in capacity of 4aF with it?
4.:Is it possible to measure capacities much larger than the specified maximum
CAPDAC range of +13pF...+21pF for the AD7746? I read something of lowering the
excitation voltage or using another capacity in series. Does that effect the
resolution/accuracy much?
5.:If I want to use an evalution board, is it really that simple, that I only
connect my capacity to the CDC and the CDC to the eval-board and that to the PC
via USB? And then I get the capacity shown in the evaluation software?


1 The major change of the Ad7747 is the Input range of 8pF ( as opposed to 4pF
for the ad7745) The power consumption is also slightly less.

2 the ARUZ is a single device whereas the REEL is a standard reel of
devices(2500 devices). The REEL7 is a smaller REEL width again.

3  Yes , 4pF is full scale, 4fFis Absolue Error - your mail is showing aF.

4 See application information in the datasheet for this information. But this
is possible.

5 I can recommend the evaluation PCB, but this has its own sensor, where you
slide a dielectric between plates. But you should be able to connect to the
Eval PCB, once your Capacitor is in this region of operation.