CMOD A7 Analog Inputs: Impedance too low for TMP36GZ?

[PeterM]

All:

I'd like to get your thoughts on the following question: 

In https://reference.digilentinc.com/_media/cmod_a7/cmod_a7_rm.pdf, page 9.  The Analog input circuit describes using a voltage divider to step a 0 to 3.3 range to 0 to 1 as required by the analog inputs.  What I am also noting (and have measured) is that the input has a 3.3K impedance.

I've been trying to get a TMP36GZ temperature monitor to work with this input and now suspect based on this temperature sensor's spec that the 3.3K draws too much current for this high impedance device.  

Has anyone else had any experience with limitation on the these analog inputs due to their lower impedance?

Peter

[jpeyron]

Hi Peter,

Looking at the TMP36GZ temperature monitor and the analog inputs on the XADC for the Cmod A7 you will need to use an active(opamp) voltage follower in between the Cmod A7 and the TMP36GZ temperature monitor for it to work. Hope this helps!

cheers,

Jon 

[PeterM]

Hi Jon:

Yes that seems to agree with my assessment about the TMP's current limit.

Thanks for confirming my suspicion.

Peter

[PeterM]

All:

Adding in an opAmp sorted out this issue.

Thanks for your feedback.

Peter