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ADS7957-Q1 Power supply sequence

Takumi Suzuki1
Mastermind 8610 points

Hi,

I would like to ask you a question about the sequence of power supply.

There are 3 power supplies, +VA, +VBD, REFP, on the device.

I understood that the sequence of these power supplies is, +VA ---> REFP ---> +VB. (from Datasheet P42)

Is my understanding is correct?

And if my idea is correct, if the opposite sequence (+VB ---> +VA) has happened, what will happen with the device?

The device will be something damaged ??

Thank you for your support.

Best Regards,

  • 0
    TI__Mastermind 45265 points
    Hi Takumi,
    The specification in ADS79xx-Q1 datasheet states that Digital I/O-supply voltage(+VBD) can range between +1.7V and +VA(Analog power-supply), so as a best practice, +VA should be powered up before or at the same time as +VBD. The Absolute Maximum Ratings section also shows that the signal input(AINP or CHn) has a restriction in that these inputs cannot exceed +VA + 0.3 V , this states that if an analog signal is present before analog power-supply, the analog core powers up in a highly probable latched-up state. This is typically a nondestructive condition, but the current through +VA can be cousumed higher than the normal current and cause the ADC to become quite hot at that time. In this condition, internal electrostatic discharge (ESD) diodes become forward biased and in turn power up the analog power-supply. To correct this, power sequence the ADC with the inputs in an unpowered or disconnected state. There is a similar situation for Reference source which should be available after analog power-supply powers up.
    I hope this is useful for you. Thanks for your post.

    Best regards
    Dale
  • 0 in reply to Dale Li
    Mastermind 8610 points
    Hi Dale-san,

    Thank you very much for your detail and kind explanation!
    I understood well.
    Best Regards,