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ADS125H02: negative pulse on AIN0

Al B
Intellectual 2900 points
Part Number: ADS125H02

From my customer...

We just observed an unexpected behavior. When we switch the input configuration (Mode4 register) e.g from AIN0-AINCOM to AIN0-AIN1 we observe a negative pulse on AIN0.

We have a big analog mux in front of AIN0 that is switched first (transition from 5.5V to ~ 2V. Then when the Mode4 register is written we can see a edge down to 1V and then a slow ramp back to the intended value.

The slow ramp is most likely due to the selected source which is high impedance in this case. When we switch to a low impedance source ( e.g. a power supply) the ramp up is much faster but the negative edge remains.

I couldn’t find any information on that behavior in the datasheet.

 

Can you explain what’s happening there?

  • 0
    TI__Mastermind 35141 points

    Hi Alan,

    Can the customer send a schematic and scope shots of the described behavior? It would also help to correlate the scope shots to the SPI transactions (if they have a logic analyzer) so we can see how the mux switching is related to the voltage droop on the inputs.

    And so I understand correctly, they are sampling 5.5V on the first external mux channel (e.g. CH1), and then when they switch to CH2 they are applying 2V, and this is where they are seeing the droop?

    You may email me personally if the customer does not want to share this information in a public forum.

    -Bryan