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External reference connection to AD7380-4, AD7381-4, AD7389-4

Category: Hardware
Product Number: AD7380-4, AD7381-4, AD7389-4

Hi Support Team,

I'd like to use AD7380-4, AD7381-4, or AD7389-4 with a 3 V external reference. Please answer a couple of questions:

1. The datasheets of AD7380-4, AD7381-4 tell that an external reference can be connected to the REFIO pin (pin #17), and the REFSEL bit must be set in the control register. But the inner schematic indicates that the REFIO pin is connected to the buffer output directly, without any switching circuitry. The question is - can you confirm that an external reference can be safely connected to the REFIO pin without causing a conflict with the internal reference which is enabled at power-up? Is it enough to apply the external reference after a small delay after the ADC's power supplies? It is not necessary to set REFSEL = 1 before connecting external reference, correct?

2. It is my understanding that AD7389-4 cannot be used with an external reference. Is that correct?

Thanks in advance,

Michael

  • Hi,

    For the AD7380-4, there is no internal reference included so an external reference should be applied to the REFIN pin.

    The AD7381-4 can be safely connected as long as the external reference must be applied after VCC and VLOGIC are applied. Analog and digital signals must be applied after the external reference is applied.

    Yes, the AD7389-4 only uses internal reference with no option to disable. 

    Regards,

    Andrei

  • Hi Andrei,

    thank you very much for your reply. One more question, just to complete he picture:

    If a 3 V external reference is connected to the REFIO pin of AD7381-4, but the REFSEL bit is not set, then the external reference will anyway overdrive the internal one, and the only reason of setting the REFSEL bit in this case is to reduce the current consumption. Correct?