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TMS320F28388D: ADC cross talk and low frequency noise added

Sheldon He
Expert 8585 points

Part Number: TMS320F28388D

Hi expert,

My customer is facing some issue on F28388D and seems related to ADC cross talk.

They test with voltage divider and divides from 3.3V DC as a test signal, then they route it to two ADC pins, ADCD5 and ADCIN14. D5 and IN14 will give different result when another ADC pin ADCA0 is connected to external circuit. (resolver encoder) Result will be the same (good) if they remove A0 form external circuit.

I saw A0 and IN14 are coming from the same group, will the noise coming from reference circuit?

Attached picture is the comparision between ADC result from D5 and IN14. Please kindly give us best assumption and what we could do next here. Thanks!

Sheldon

  • 0
    TI__Guru 60865 points

    Hi Sheldon,


    What ADC(s) is channel 14 being sampled by?  Is A0 being sampled, or just connected without being sampled? 

    What is the impedance of the voltage divider driving the test input, what capacitance has been placed on the this ADC input pin, what is the sample rate, and what is the S+H duration being used?   


    The methods for simulating the input circuit in the following app. note may be useful for understanding if the behavior is expected: https://www.ti.com/lit/an/spract6/spract6.pdf