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ADS1119: DRDY interrupt stops working

Part Number: ADS1119

Dear all,

We are using the ADS1119 in our current design, and it is configured to continuous conversion, data rate of 20 sps and we are using the four channels single ended.

As expected, the DRDY generates an interrupt at every 50 ms, but we observed that sometimes it take longer to finish the conversion, and eventually it stops completely.

It will only work again if it is reinitialized via I2C.

We couldn´t find any information regarding this issue in the datasheet. Do you have any idea why this happens?

Below you can find images of the DRDY signal, with the interrupts evenly spaced in the first picture and with the longer delay in the second picture.

Thank you in advance.

  • Hi Ivan,

    There is information in the datasheet, but it may not be totally clear.  First consideration is DRDY does not go back high until the RDATA command is issued which latches the conversion result into the output data buffer forcing DRDY high.  So when DRDY is low, data is available to be read, but for some reason you are not doing so in your code (which applies to the second scope shot).

    In the first scope shot there appears to be one elongated response between the second and third pulses of DRDY.  This could be due to a configuration change.  When you write to the configuration register, the conversion will restart following the latch of data into the register.  Depending on the timing of when the conversion data are read out and the change of the configuration there could be an extended period of time before the next conversion result is ready to be read from the device.

    Best regards,

    Bob B

  • Hi Bob,

    Thank you for your answer. We will look into our code and analyze the data with the logic analyzer.

    However, the case you mentioned about DRDY going back to HIGH after a RDATA command does not only apply to single conversion mode ?

    According to the datasheet we can read:

    " Data Ready (DRDY)
    DRDY is an open-drain output pin that indicates when a new conversion result is ready for retrieval. When DRDY falls low, new conversion data are ready. DRDY transitions back high when the conversion result is latched for output transmission. In case a conversion result in continuous conversion mode is not read, DRDY releases high for tw(DRH) before the next conversion completes. See the I2C Timing Requirements table for more details."

    In our case, we are using continuous conversion mode, that´s why we were expecting DRDY going back to HIGH.

    Best regards,

    Ivan Bastos

  • Hi Ivan,

    The DRDY will go high after the conversion result is read in either single or continuous conversion modes.  In continuous mode there is a pulse for about 8us (2 tMOD periods) if the previous conversion is not read from the ADS1119.  I suspect that the scope does not pick up this short of a pulse for display at 100ms per division.

    Best regards,

    Bob B