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ADS8363: Using only one reference

Kate
Prodigy 40 points
Part Number: ADS8363

Hello,

I am using this ADC on my board with the device configured to use only one shared reference (REFIO1) for both internal ADCs on the chip. The resulting data was extremely noisy to the point that we were only able to use 12 bits of what should have been 16 bits of data.

I tried the following:

  1. Configured the device to use the second reference (this improved the noise).
  2. Reconfigured the device to use only one reference, but changed the hardware to add a 22 uF capacitor between REFIO2 and RGND (this also substantially improved the noise).
  3. Combined (1) and (2) (this provided an extremely clean reading). 

It is unclear from the datasheet why (2) above would help when we were not even using the second reference. Do you have an explanation for this?

Additionally, can you explain why using a single reference was so much worse than using two? The datasheet did not indicate that it was invalid to use only one. 

Thanks in advance for your help. 

  • 0
    TI__Guru 66166 points

    Hi Kate,

    Thank you for your post.

    Since you are only using one REFIOx voltage, is REFIO2 disabled (i.e. default setting)? If there is no capacitor on REFIO2 while enabled, perhaps there is some noise coupling into the device. Otherwise, it should be ok to leave REFIO2 floating or connected directly to ground when disabled.

    Normally, it would be fine to use a single REFIOx voltage to drive both ADCs, provided there is sufficient decoupling capacitance on the REFIOx pin. Did you already have 22 µF on REFIO1 to RGND in your original testing? 

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 40 points

    Hi Ryan,

    Thank you for your response.

    Although I was not using REFIO2 in my original testing, it was enabled. It sounds like that was likely my problem. I will try disabling it and see if that improves my noise results when only using one reference (and having REFIO2 floating in hardware).

    To answer your other question, yes, REFIO1 did already have 22 uF in my original testing.

    Thanks again.

    Kate