Tool/software:
Hi Team,
I'm running into a strange issue with the ADS7828 ADC. I'm getting noisy readings, but only when sampling certain channels.
Here’s what I’ve observed:
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Channels CH0 and CH1 are connected to potentiometers (voltage dividers) — readings are stable and clean.
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Channels CH2 and CH3 are both driven from op-amps (ISL28191FHZ-T7) doing voltage level shifting.
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When reading CH2, the data is clean and if I scope CH3 while reading CH2, there’s no sign of noise.
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But when I read CH3, I get a small AC waveform on the input pin of CH3 — looks like a disturbance or charge injection occurring during the read.
It seems like the act of sampling CH3 is somehow injecting or drawing charge, causing this noise. I'm wondering:
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Could the op-amp output impedance be too high to drive the ADC’s internal sampling cap effectively during acquisition?
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According to the ISL28191 datasheet, output drive seems pretty good, but maybe not for fast charge transients?
Has anyone run into this before with the ADS7828? Would buffering with a lower output impedance op-amp or adding a series resistor + small cap help stabilize the signal?
Cheers for any ideas!
