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AFE5808A: External reference mode

David Christian
Prodigy 60 points
Part Number: AFE5808A

I am interested in using the external reference mode of the AFE5808A.  Do I understand correctly that this will shift the common mode of the internal pipeline ADCs, and that if I want to shift the common mode by 40% of the ADC range (so that an open input will yield an output of ~10% greater than the smallest possible numerical ADC output) I should set the voltage at pin M3 to 0.4V?

The data sheet also refers to an external reference current, but I don't see a description of how this would be used (what pin to connect to, for instance)... I'm probably just not looking carefully enough.  I don't think I want to use an external current, but I'm curious about how I would do so and when I might want to.

  • 0
    TI__Expert 4675 points

    Hi,

    In this device ADC needs a reference voltage to operate. This is not the common mode of ADC . Either we can give the refence externally or by default reference is generated internally. 

    When you force the reference voltage from external world device expects a small current and the external source of this voltage must be able to give that current .

    Please refer to this section in datasheet for more detail on this.

    9.2.2.4.2 ADC Reference Circuit

  • 0 in reply to Sachin H K
    Prodigy 60 points

    Thank you.  I think I understand, but I'd like to make sure.  Do I now understand correctly that the reference voltage is not a control that can be set to (1.4 minus V) where V can be an arbitrary voltage (in some allowable range), but rather a reference voltage that must be set to 1.4 Volts and must also provide a reference current?  Is the internal reference produced by a bandgap reference circuit or similar?

  • +1 in reply to David Christian
    TI__Expert 4675 points

    David,

    Yes . Reference voltage is not a control voltage and you must be set it to 1.4V . This should be able to give reference current . So to conclude we need to give external reference voltage of 1.4V. 

    Yes internal reference is generated using bandgap.