AD7763 - valid output data

Hi all, 

I am using the AD7763 in a two daisy-chain configuration with SPI interface. 

By checking the status register value returned by the ADC, when appling a waveshape to the input I can see packet coming with not valid data (DVALID = 0). OVR is not set though. 

It is not affected by the Decimation (using X64 decimation, but even with X16 shows the same), nor by the LowPower setup. No filters have been activated.

Why is that happening? 

Statur register format:

 

Thank you,

Luca

  • 0
    •  Analog Employees 
    on Apr 3, 2019 8:59 AM

    Hi, Luca.

    Let me check on this and get back to you. However, can you provide more details about your system sequence or settings? Are you in default settings? If you could also provide the schematic and as well as your input settings, that would be helpful. Have you followed the recommended sequence in using the part? Following a SYNC, the digital filter needs time to settle before valid data can be read from the AD7763. The time from the rising edge of SYNC until the DVALID bit is asserted is dependent on the filter configuration used.  

    Thanks,

    Jellenie

  • Hi Jellenie, 

    thank you for your reply.

    Indeed our current system is the one previously discussed here (almost 2 years ago).

    https://ez.analog.com/data_converters/precision_adcs/f/q-a/24085/ad7763-with-shared-spi-bus

    We are currently using a software SYNC pulse (through the internal register, sent with broadcast address). 

    The system is working fine, however in some cases, few AD7763 are sending back data with 0 on the DVALID bitmask. Not sure why yet. And once started, it will periodically send not valid packets. 

    Does the AD7763 data valid mechanism might be impacted by overheating? Yet it shows it even when booting from a cold startup. 

    Do you suggest to use a hardware SYNC signal? If so, why it is not impacting the other AD7763 we use? 

    Thank you,
    Luca