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TMS320F28075: Handling VREFHI when internal reference is enabled

Hang Yang
Expert 3596 points

Part Number: TMS320F28075
Other Parts Discussed in Thread: OPA320

Hi Experts,

My customer is using F28075 and F28P55, they would like to know how to handle VREFHI when internal reference is enabled?

The use case is that customer is developing a compatiable design that two software, which use internal and external refernce repectively, and will share one board, in which the VREFHI is connected to a external refernce.

Is it ok to let VREFHI connected when internal reference is use?

Note that two devices is concerned, F28075 and F28P55.

Regards,

Hang

  • 0
    TI__Mastermind 41690 points

    Hi Hang,

    When internal VREFHI is configured, the internal bangaps for reference also come out of the VREHI pin so if the is already an existing external source the powers VREFHI, that will cause contention and produce erratic VREFHI voltage and conversion results.  One solution that you can suggest for customer is to buffer the external VREFHI source with an opamp with a tristatable output.  One example is the op amp OPA320.  Customer can configure a unity gain buffer for the external VREFHI and enable the OPA320 output only in external VREF mode with SHDN pin tied high.  For internal VREF mode, tie the SHDN pin of the OPA320 to 0 to disable the output.

    Another option is just to use a simple SPST switch to connect/disconnect the external VREFHI.

    Regards,

    Joseph