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ADS131A04: Time delay between WAKEUP Command and sampling

Hao Wang14
Expert 4415 points
Part Number: ADS131A04

Hi Team,

When WAKEUP command is sent, ADS131A04 should start to sample at the input, what's the time delay between the WAKEUP command and sampling in Asynchronous Interrupt Mode?

Thanks and Best Regards!

Hao

  • 0
    TI__Guru* 93635 points

    Hao,


    The ADS131A04 should start the ADC immediately after the WAKEUP command. However, it does take some time to get the data from the device.

    There are two things that add to the delay of reading from the device. First, the ADS131A04 has a sinc3 filter. This is basically a three-unit moving average of the data taken from the ADC. It will take data periods before this data is fully settled. You can see this in Figure 51 in the datasheet:


    Second, there is a data buffer for DOUT that adds one more period of latency for the ADC data. This means that the data that completed at the 3rd /DRDY period will not appear at DOUT until the 4th /DRDY period.

    Hopefully this answers your question. If you have other questions about this device, you can post again, or start a new thread.


    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Expert 4415 points

    Hi Joseph,

    Thanks for the detailed confirmation. After receiving the WAKEUP command, there should be some time delay to start to sample in theory because the internal circuit cannot respond immediately, usually this time delay should be very small, so can you help confirm if this time delay is within 1us?

    Best Regards!

    Hao

  • 0 in reply to Hao Wang14
    TI__Guru* 93635 points

    Hao,

    I've contacted the design group to see if they have a time for the startup. I'll post back when I hear from them.


    Joseph Wu 

  • 0 in reply to Joseph Wu
    TI__Guru* 93635 points

    Hao,


    I've checked with the design group and the device is enabled as immediately after the WAKEUP command is decoded by the device. If the CRC is disabled, then this is as the last SCLK falling edge of the first word for the command. If CRC is enabled, the command is decoded at the last SCLK falling edge of the frame.

    We had been concerned that when the device is in STANDBY, the reference would also be shut down. This could have been a problem with the WAKEUP command because if the reference needed to be started up too. The reference startup could take several milliseconds depending on the capacitance load of the reference. However the reference enable is independent of STANDBY and WAKEUP. The reference is always on when enabled, so this should not affect the startup if the reference is already enabled or if an external reference is used.


    Joseph Wu