Regarding REF_MUX_CTRL[7:6] bitfield for Internal reference on EVAL-AD7779FMCZ(AD7779)

Hello

I configured a circuit according to (figure 98. SPI Control Mode Connection Diagram with Internal Reference in AD7779 datasheet)

Sampled ADC value is stable and normal on default setting of REF_MUX_CTRL[7:6]=[00].

Do I have to configure REF_MUX_CTRL[7:6] bitfield to [01] to operate internal reference?
or Is it okay to configure both options [00] or [01] with the connection of internal reference?


Best regards,

Kye-Hyun Park



added a question
[edited by: hellokyehyun at 7:22 AM (GMT 0) on 22 Feb 2019]
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  • +1
    •  Analog Employees 
    on May 10, 2021 9:31 AM

    Hi, 

    Apologies for missing this item. But to answer this query. You can use either of the two settings. The figure 98 you mentioned, is a suggested way to connect the internal reference to the external reference's input (but remember to configure the ADC as external reference REF_MUX_CTRL[7:6] bitfield to [00] ).The advantage of connecting it that way is to allow adding an external low pass filter to improve performance. But configuring it with internal reference  REF_MUX_CTRL[7:6] bitfield to [01] is also okay. You can see the difference as shown on figure 92.

    Thanks,

    Jellenie

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  • +1
    •  Analog Employees 
    on May 10, 2021 9:31 AM

    Hi, 

    Apologies for missing this item. But to answer this query. You can use either of the two settings. The figure 98 you mentioned, is a suggested way to connect the internal reference to the external reference's input (but remember to configure the ADC as external reference REF_MUX_CTRL[7:6] bitfield to [00] ).The advantage of connecting it that way is to allow adding an external low pass filter to improve performance. But configuring it with internal reference  REF_MUX_CTRL[7:6] bitfield to [01] is also okay. You can see the difference as shown on figure 92.

    Thanks,

    Jellenie

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