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ADS8684A: About startup sequence

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Guru 21045 points

Part Number: ADS8684A

Hi Team,

 

I have two questions for startup sequence.

 

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[Q1]

I understand that DVDD(+3.3V) must be less than AVDD(+5V).

When Startup, is there any limitation?

(For example, DVDD or AVDD slew rate, Stable time etc.)

 

[Q2]

After AVDD and DVDD are supplied, when does the internal circuit become active?

So, we would like to know the timing that ADS8684A can convert the analog input to the digital data.

-----------

 

 

Regards,

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  • 0
    TI__Mastermind 25070 points

    Hello,

    It is best to keep AVDD always higher than DVDD, even during start up. But a good rule of thumb is if DVDD is above AVDD during start up, to keep it less than 300mV greater than AVDD.

    the DVDD and AVDD supply the digital and analog side, respectively, independently of each other. Meaning that one side may be table before the other. if DVDD is ramped up, but the analog power supply is not. The device will be able to start and complete conversion, but the analog measurements will be no good.

    the opposite is true as well, if the analog power supply is stable, but DVDD is not, then the communications will be no good.

    Once both supplies are stable, then the device will operate as expected.

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Guru 21045 points

    Hi Cynthia-san,

    Thank you for the detail information.

    I understand. Thank you very much.

    Regards,

    Hide

  • 0 in reply to Hide
    Guru 21045 points

    Hi Cynthia-san,

     

    I have additional question.

     

    [Q3]

    Slew late of DVDD is high so DVDD higher than AVDD during 5ms.

    Then, could you please let us know if you have any concern (device is broken / malfunctions etc.)?


     

    Regards,

    Hide

  • 0 in reply to Hide
    Guru 21045 points

    Hi Cynthia-san,

    What do you think about the present situation regarding this matter?

    I undersatand that this usage don't have problem.

    Is my understanding correct?

    I’d greatly appreciate your verification.

    Regards,

    Hide

  • 0 in reply to Hide
    TI__Mastermind 25070 points

    Hello,

    Apologies, I was out of town. But I saw that you posted this on a separate thread. I will go ahead and respond there.

  • 0 in reply to Cynthia
    Guru 21045 points

    Hi Cynthia-san,

    Thank you for your reply.

    I will reply to a different thread.

    Regards,

    Hide