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ADS7953: Power up sequence requirement

Zeki Sisman
Intellectual 320 points
Part Number: ADS7953

Hi,

I am using ADS7953 with VA = +3.3V, VBD = +2.5V. Datasheet states: "The analog supply is always greater than or equal to the digital supply.". This same question is asked couple of times here but I am still confused with given different answers.:

http://e2e.ti.com/support/data-converters/f/73/t/865233?ADS7953-Power-up-sequence --> TI says no need for power up sequencing.

https://e2e.ti.com/support/data-converters/f/73/t/498035?Power-up-requirements-of-ADS7953-for-analog-and-digital-supplies --> TI says VA should be powered before or at the same time.

https://e2e.ti.com/support/data-converters/f/73/t/839210?ADS7953-Timing-sequence --> TI says it's better to turn VA ON first, otherwise chip can act abnormally.

https://e2e.ti.com/support/data-converters/f/73/t/476201?ADS7954-Power-on-sequence --> TI says ideally VA and VBD are ramped together but VA  is always greater.

My question is:

  • I turn +2.5V for VBD ON first, VA is at 0V. Then, after 5ms delay the +3.3V VA turns ON and settles. After 1 second I start communication through SPI. Would I have any problem? Do I have to sequence power on to make sure VA>VBD always or not?

Kind regards,

Zeki

  • 0
    TI__Mastermind 24940 points

    Zeki,

    You are right that there has been some inconsistencies in this, but one thing seems consistent and conforming with the datasheet is that VA needs to always be greater or equal than VBD. The first post you listed was my response, and that response should be elaborated to clearly state this.

    It is not known how the device will behave if VBD is ramped fully before VA, but I predict there will be a greater current consumption during this time. That is not to imply that the device will begin normal operation once both supplies are settled.

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Intellectual 320 points

    Hi Cynthia,

    Thank you for the quick response.

    Then I understand device can malfunction or even get damaged in such a scenario. And correct operation is not guaranteed after supplies are settled.

    To sum up, yes there is a power up sequence requirement for ADS7953. Is this the case?

    Kind regards,

    Zeki

  • 0 in reply to Zeki Sisman
    TI__Mastermind 24940 points

    The power supplies do have requirements to follow, VA needs to be greater of equal to VBD at all times, this includes power up