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ADS8681WEVM-PDK: Regarding AVDD and DVDD

ttd
Mastermind 9395 points

Part Number: ADS8681WEVM-PDK
Other Parts Discussed in Thread: ADS8681

Dear Technical Support Team,

I have a question regarding the schematic for the ADS8681 series evaluation board (ADS8681WEVM-PDK Evaluation Module).

This is related following my post.

ADS8689: The Effects of DVDD Voltage - Data converters forum - Data converters - TI E2E support forums

Q1

It appears that AVDD is regulated by the TPS7A4901DGNR and is set to 5.01V, but the circuit for DVDD seems to operate on the USB voltage (5.5V?).
Since this is below the absolute maximum rating of 7V, I don’t think it will cause a failure, but DVDD > AVDD, which is outside the recommended range. Is this acceptable?

Q2

since AVDD is generated from the USB power supply for DVDD, I believe DVDD will always be higher than AVDD at power-up due to startup delay.
Since this also does not exceed the absolute maximum rating, can I assume this is acceptable?


Best Regards,

ttd

  • 0
    TI__Expert 8310 points

    Hello ttd, 

    The ADS8681WEVM is paired with our PHI controller, this controller does provide a few power options for the EVMs connected to it, none which are direct USB sources. The power sources available do originate from the USB power but they all go through some power management system before they make it into the EVM. 

    The controller provides the option of 4 sources: 

    • EVM_REG_5V5 - 5.5V 
    • EVM_RAW_5V  - 5V
    • EVM_DVDD - 3.3V (all digital signals on the PHI are set to 3.3V logic level)
    • EVM_ID_PWR - 3.3V (this one is exclusively used for the EEPROM that is placed on EVMs to identify the board and confirm paring with through the GUIs)

    The ADS8681EVM ties the EVM_DVDD to the DVDD supply:

    There should be no concern of DVDD > AVDD when using the ADS8681EVM-PDK. 

    Thank you for asking though. 

    Best regards, 

    Yolanda