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ADS7828 Having Vref hooked to 5V but selecting internal Vref in the I2C bus.

Other Parts Discussed in Thread: ADS7828

It is unclear on the ADS7828 datasheet, what happens if you connect a voltage to the Vref pin but select "use internal reference" when reading the values? i.e. what happens if I send PD1 and PD0 as both one, but have 5 volts hooked to pin 10 (Vref in/out)?

  • Hi Sam,

    The device powers-up by default with the internal reference disabled; therefore using the external 5V supply as a reference is not an issue provided that AVDD is at least 5V.  If you intend to use the internal 2.5V reference, the REFIO pin must be left floating and only connected to a bypass capacitor.  The internal reference buffer drives (or attempts to drive) the REFIO pin to 2.5V when the internal reference is selected. 

    Let me know if you have additional questions.

    Best Regards,

    Luis

  • The Linux driver defaults to using the internal reference, what will happen if I don't re-configure the driver and I have Vref plugged into a 5V source.
  • Sam,

    The internal reference buffer will attempt to drive the REFIO pin.  The datasheet does not specify the max output current of the reference buffer; however, the buffer will consume higher current and the device may not operate as specified or may not be biased as intended.  If you intend to use the device with external reference,  the recommendation is to disable the internal reference on the software.

    Regards,

    Luis

  • Thanks for answering, I finally got my driver to turn off the internal source and it worked properly.