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TMS320F280039: ADC B2 has larger offset

Terry Deng
Expert 3015 points

Part Number: TMS320F280039

Tool/software:

Customer measure F280039 ADC-B2 pin has larger offset which >1000LSB when B2 pin is floating without any connection, and it is only happen on 80pin package but not in 64pin package, may I get advice if anyone has hear this behavior and know possible reason?

  • 0
    TI__Guru* 82610 points

    Terry,

    We can't guarantee ADC conversion behavior on any floating pin.  Design wise there is no difference in the signal pin B2/C6 from the 80 pin device to the 64 pin device.  Most often a floating analog input pin will simply give the charged state of the internal S/H capacitor.  If there has been a recent ADC conversion on a driven pin, the residual charge on the cap will be similar to that last sampled voltage.  If the ADC has been idle for some time, the S/H cap charge will trend to the common mode of the ADC, which I believe is either VREFHI/2.

    Best,

    Matthew