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FMCOMMS production testing

Question asked by oclabbao on Jan 27, 2016
Latest reply on Feb 3, 2016 by oclabbao

Hi,

 

I'm trying to understand production testing of FMCOMMS2/3/4, so we can port it to a custom but similar board with AD9361 and AD7291.

 

I'm looking at the following:

https://wiki.analog.com/resources/eval/user-guides/ad-fmcomms2-ebz/testing

https://github.com/analogdevicesinc/iio-oscilloscope/tree/master/profiles

 

Specifically for the Voltage section, the wiki says:

"Since VDDA_GPO ... comes from 3P3V (on the schematic) ..., we can assume that things will be 3.3V ± 5%, or 3.135V to 3.465V. This 3.135V to 3.465V translates to 1.959375 to 2.165625V (due to the 10k/16k voltage divisor)."

Further on the iio-oscilloscope github (see FMComms2_test.ini), it says:

# These numbers are determined by the:

# - resistors on the PCB (10/16k), in this case * 0.625

# -full scale and refernce, in this case 0.00061

Also, looking at the schematics, it shows the AD7291 inputs are taken from the voltage across the 16K resistor.


Unless I am missing something, shouldn't the voltage division be 16k/(10k+16k) or 0.6154, instead of 10k/16k or 0.625?


Once the actual voltage values are computed, I've no problem translating that to ADC readings. It's just that the values displayed on the wiki and test profiles seem to be a little off.


Thanks in advance for the clarification.
- orvs

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