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TMS320F280049: VREFHI monitoring/diagnostics

Michael Shklyarman
Genius 12760 points
Part Number: TMS320F280049


Champs,

Customer has decided to use internal 1.65V reference for the ADC but requires to monitor this voltage. Are there any facilities inside the chip to support this (e.g. connection to ADC)? If that is not possible another way the customer considers is to connect VREFHI to VDAC, then connect the DAC output (e.g. DACB_OUT) to an ADC input externally. would that be a good way? any insights/recommendations are greatly appreciated!

regards

Michael

  • 0
    TI__Guru 60865 points
    Hi Michael,

    VDAC input is also an ADC input, so you could probably just sample the VREFHI on that ADC pin directly.

    Really the issue is that whatever method you use, as VREFHI changes the converted results will change as well, so it will be hard to detect an issue with the reference.

    e.g. if VREFHI = 1.65V then the reference range is 0 to 3.3V and 1.65V sampled will result in (1.65V / 3.3V)*4096 = 2048
    e.g. if VREFHI = 1.60V, then the reference range is 0 to 3.2V and 1.60V sampled will result in (1.60V / 3.2V)*4096 = 2048

    Now it may make a little more sense if you use the 100-pin package where there are two independent VREFHI pins; you can cross-sample the two VREFHIs onto ADCs not associated with the reference.

    I think a better method to verify the reference voltage would to be to source in a known good voltage (e.g. 2.5V from REF5025) and then sample that voltage to determine if the reference is good. If the intref voltage starts to droop, the sampled voltage will start to increase.
  • 0 in reply to Devin Cottier
    TI__Genius 12760 points
    Hi Devin,

    The customer's approach is that the DAC reference (VDAC) would be tied to VDDA via an external connection. Their VDDA is rated 2% over temperature and current, and they have diagnostic on it. So by sampling the DAC output with the ADC, they should be able to obtain a direct accurate measurement of VREFHI. Right now all of VREFHIs are tied together. Do you think this would work?
    Also on similar note the c2000 safety manual seems to suggest that there is a way to do the loopback connection internally, without going out to the PCB. The Analog subsystem block diagram in the TRM shows "Analog Interconnect" that might be used to connect DAC to the ADC but there is no description of how to control it. Do you think this is feasible?

    thanks
    Michael
  • 0 in reply to Michael Shklyarman
    TI__Guru 60865 points

    Hi Michael,

    Supplying VDAC with VDDA seems like a reasonable strategy.  

    To check the internal/external pin connections, see Table "Analog Pins and Internal Connections" in the datasheet (and also I think this is duplicated in the TRM).  This table basically defines what is in the "Interconnect" portion of the diagram.  

  • 0 in reply to Devin Cottier
    TI__Guru 60865 points
    This thread is being handled offline.