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ADS131A02: Input clock lost detection

Hisao Uchikoshi
Genius 14940 points
Part Number: ADS131A02

Hi Experts,

The ADC clock is supplied externally. My customer wants to detect the input clock lost for safety operation. 

Are there any way to detect input clock lost? One of the idea is to read register data over SPI from host MCU periodically. Read only register like ID_MSB returns 0x02 but when missing clock, ADC returns 0xFF. Are there any idea? 

Regards,

Uchikoshi

  • +1
    TI__Guru 66566 points

    Hello Uchikoshi-san,

    Thank you for your post.

    I believe the register contents and the SPI interface are still read/write accessible, even when there is not a master clock present. Therefore, reading the ID register would not be a valid test for missing host detection.

    One option would be to monitor the /DRDY pin. This pin will toggle when a new conversion result is ready to be read. However, if there is no master clock input, then the modulators will stop converting and /DRDY will no longer toggle. This assumes that the ADC channels are enabled and the device is not in STANDBY Mode. 

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    TI__Genius 14940 points

    Hi Ryan,

    Sorry to asking you again. There is a feedback from customer. PCB is already fixed but /DRDY pin is not routed to MCU so need to find other solution by using software. There are serval FAULT bit in registers. Are there any FAULT bit which are affected by external clock lost?

    Regards,

    Uchikoshi

  • 0 in reply to Hisao Uchikoshi
    TI__Guru 66566 points

    Hello Uchikoshi-san,

    I've asked the digital designer to help clarify which FAULT bits in the register map would be set when an external clock is missing. We're also looking into some other indirect ways of checking this.

    Can you share a simplified schematic so we know which pins are connected to the host and which interface mode is used?

    Regards,

    Ryan

  • +1 in reply to Ryan Andrews
    TI__Guru 66566 points

    Hello Uchikoshi-san,

    Thanks for the added details in your email.

    It does not seem to be possible to implement missing external clock detection in Asynchronous Slave Mode. We were considering the Watchdog Timer, but this would only work if the customer uses the Synchronous Master Mode, which relies on the internal oscillator timing.

    Regards,

    Ryan