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ADC128S052: Wrong data when reading the first time all 8 channels

reto.gaechter
Intellectual 260 points
Part Number: ADC128S052

Hello

We are using the ADC128S052 and getting wrong data when reading them out for the first few cycles. Only channel IN0 0 seems to be correct, reading  IN1 results in completely wrong data. Instead of 12 bit we get 25273.

When doing the read access to all channels the 5th access to the 8 channels will be correct

Before the first access is done we are making a pause to make sure that all voltages are in steady state.

What the could be the root cause of this behavior.

Thanks

Reto

  • 0
    TI__Mastermind 25020 points

    Hello,

    What mode of operation are you using? Meaning, are you changing CS states with each conversion, or is CS help low for all conversion.

    I suggest using an oscilloscope to debug, connect the probes to the digital communication pins, CS, SCLK, SDI, SDO

    This will provide a visual check to timing and communication, and can verify that the firmware is acting as expected.

    Please provide an oscilloscope shot of the incorrect.

    Also use different known DC input values for each channel for debugging as well. ex, Ch0 = gnd, ch1 = 1V, all within the input range. this will help to see if any patterns, or wrong channels are being read inadvertently

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Intellectual 260 points

    Hello Cynthia

    Sorry for the long answer time.

    We are changing the CS.  After 4 times of reading the data the values are ok. There are no problems known during the read of the first samples?

    Kind regards

    Reto

  • 0 in reply to reto.gaechter
    TI__Mastermind 25020 points

    Hello Reto,

    There should be no issues with reading conversion results.

    There is no need to incorporate a power-up delay or dummy conversion as the ADC128S052 is able to acquire the input signal to full resolution in the first conversion immediately following power up.

    The first conversion result after power-up is that of IN0. and the second conversion after that will be of the channel selected in SDI.

    Can you share a scope shot of the incorrect results.

    Also, can you confirm that the inputs to the device are settling during the incorrect conversion results. Measuring the input at the ADC input to confirm that the input voltage is as expected.

    Is there a pattern in incorrect results?

    Regards

    Cynthia