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ADC128S052: About the input capacitor of ADC128S052.

user1731820
Prodigy 30 points

Part Number: ADC128S052

I adopted your ADC128S052CIMTX / NOPB, but when I checked the AD value that was taken in, it was found that the fluctuation was large (about ± 3%).
After checking the situation, the data sheet of ADC128S052CIMTX / NOPB recommends 1uF + 0.1uF as the input capacitor, so it was mounted as an input capacitor, but the reference power supply adopted depends on this load capacity , It was oscillating.
It is best to change the reference power supply, but since we have already manufactured the board, we are considering whether it can be supported by changing the constant.
As a test, when I removed the capacitor, the oscillation stopped, but noise occurred at the timing of AD conversion.
Therefore, when only 0.1uF was used, there was no oscillation or noise, and there was no fluctuation in the AD value.
Also, when 0.1uF was changed to 0.01uF, noise such as spike noise occurred, but the AD value did not fluctuate.
Even if the input capacitor is made smaller, it seems that the AD value is not affected. Is there any problem?

Thank you for your reply.

  • 0
    TI__Guru**** 182551 points

    Hi there!

    I suspect you are talking about the bypass capacitor recommendation for the ADS128S052 on pin VA.  This supply voltage also acts as the reference for the ADC.  If this voltage is oscillating with a 1uF load applied, I suspect the issue is with the source of VA as you mentioned.  Are you using a linear or switching regulator to supply VA to the ADS128S052? 

    If you are satisfied with the conversion results using only a 0.1uF bypass capacitor on VA, that is fine - you won't damage the ADC.  You may however see different results over various production lots.  You should consider fixing the power supply.