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MK10 ADC input sampling waveform

Question asked by Wei Xu on Sep 17, 2018
Latest reply on Sep 20, 2018 by Robin_Shen

Hi team,

We are using MK10DN512VLQ10 in our system. During ADC testing, I found that ADC error will change according to external input voltage. So I removed all external capacitors and applied a standard voltage source to the input circuit ,

then I measured the voltage on the pin and saved the screenshots as below(probe was AC coupled with short spring type ground):

I thought a typical ADC sampling waveform should only contain negative spike(due to charging of internal sampling capacitor), but I also captured some positive spike and sometimes even change from positive to negative(the last screenshot above). I also didn't expect the first unusual high level spike.

 

The modified external circuit just like below:

 

 

Below is the test setup, this is a NTC sensor circuit with capacitor removed and NTC disconnected. The voltage is given by a voltage generator, I also checked the output of the voltage generator, no spike was found.

 

Are those behavior caused by the internal design of the MCU?

Please help!

 

Thanks and regards!

Wei Xu

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