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ADC3569: VREF on GPIO0

Mark Lanciault1
Prodigy 170 points

Part Number: ADC3569

I'm using ADC3569 in a pulsed AC application. Shorter pulses are fine, but longer ones exhbit a negative low frequency hump on the digitized waveform just after the pulse is processed but not seen on either differential input pin. Thoughts go to maybe the reference is dipping. Only thing I can find on the datasheet on stabilizing the reference is below, and that is only when using an external reference. The EVM has no capacitance, so I didn;t use any. Has anyone seen this sort of behavior before? Should the capacitances defined below be placed on GPIO0 to help stabilize the reference?

  • 0
    Prodigy 170 points

    Sorry, typos above. All should refer to GPIO1.

  • 0 in reply to Mark Lanciault1
    TI__Prodigy 390 points

    Hi Mark,

    a 10uF and a 0.1uF ceramic bypass capacitor (CVREF) between the GPIO1 to AGND pin and placed as close to the pins as possible, Have you tried your experiment in internal reference mode. GPIO0/1 has multiple configuration options due to this reason caps might not been installed.

    Regards

    Samba. 

  • 0 in reply to Sambasiva Rao Kotha
    Prodigy 170 points

    Hi Samba,

    Sorry, I think you're confused. I am using the internal reference, but I'm seeing a response on the ADC digitized output showing a long negative hump just after the receipt of a short AC sinusoid burst that looks suspiciously like the reference responding to the pulse with it's slow response time. I was wondering if putting the two caps on GPIO1 would help stabilize the reference, or are the GPIO off by default? I'm basically trying to see if this is a reference issue or not without moving to the use of an external reference, Any ideas?

  • 0 in reply to Mark Lanciault1
    TI__Prodigy 390 points

    Hi Mark,

    if your using in internal reference mode and GPIO1 is in unused state if you place caps that will not help, Caps are needed only in external reference mode. Your thoughts on the reference is dipping-->we can't directly measure internal reference.

    I will check with the other engineers around me for possible root cause, mean time you can go to external reference mode and check if that help.

    if external reference mode doesn't help please come back with your register configuration/schematics/intended adc mode for faster debug.

    Regards,

    Samba.