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Original question:

DAC80502:About using an external reference

DAC80502: Waveform at power-on

Taroimo
Intellectual 680 points
Part Number: DAC80502


Dear TI team

 

We have confirmed a waveform in which the VREFIO voltage momentarily exceeds "VDD + 0.3V".

The VOUT pin of the REF5050 and the VREFIO pin of the DAC80502 are connected directly without a resistor.

However, since this waveform is seen only momentarily when the power is turned on, we believe that there is no risk of damage to the device due to excessive heat.

Is this perception correct?

 

Best Regards,

Taroimo

  • 0
    TI__Mastermind 42273 points

    Hi Taroimo-san, 

    We we don't recommend any stresses beyond the absolute maximum ratings for any period of time. Your situation may be a lower risk (it likely won't stop functioning immediately), but we wouldn't be able to guarantee that over time there wouldn't be any damage or reduction in performance as the part is powered on and off in the application. 

    Is there any way to limit the supply of the REF5050 until after the DAC has powered on? 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Intellectual 680 points

    Hi Katlynne,

     

    Thanks for your help.

    And sorry for the late reply.

     

    There is currently no way to limit the REF5050 supply until the DAC is powered on.

    In addition, the circuit this time is based on the "DAC80502EVM".

    When "JP4" is set to "short" on this EVM circuit, the "VREFIO" pin of the DAC80502 is set to "internal" by default, so the outputs of the REF5050 and the DAC80502 collide at least during power-up.

    Therefore, it is possible that the same phenomenon as above can be confirmed.

    I would like to know if there is a countermeasure other than limiting the supply of the REF5050 until the power of the DAC is turned on.

     

    Best Regards,

    Taroimo

  • +1 in reply to Taroimo
    TI__Mastermind 42273 points

    Hi Taroimo-san, 

    The internal reference and REF5050 colliding at powerup is a different issue from the REF5050 powering on before the DAC VDD has been powered on. 

    You should not apply any voltage greater than VDD to the DAC pins. This comes from the absolute maximum ratings, and we cannot guarantee the performance of the part in the long term if you are violating the absolute maximum ratings for any time. 

    It is true that the internal reference will collide with the REF5050 at powerup but this is not at risk to damage the part. The series resistor recommended by Paul in your last post would help keep the power dissipation (and any excessive heat) until you can disable the internal reference. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Intellectual 680 points

    Hi Katlynne,

     

    Thank you for your reply.

    We will consider countermeasures in the direction of delaying the startup of the REF5050.

     

    Best Regards,

    Taroimo