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DAC121C085: Power on reset

Robin Liu
Intellectual 1660 points
Part Number: DAC121C085

Hi all,

A customer uses the DAC121C085. in their application scenario, the machine power will sometimes frequently power down and power up. then in some case, the part will work wrong. So as stated in datasheet, the power on reset have to make sure the Va raise from below than 200mV. it seems to be correlated.

so the customer question is:

1）how to avoid this power on reset failure or do we have some workaround?

2) do we have other DAC part don't need to make sure the correct power-on-reset must less than 200mV

Regards

Robin Liu  

  • 0
    TI__Genius 14220 points
    Hi Robin,

    Thank you for your query. I am suspecting some power supply decoupling issue here. Could you please upload the schematics? In case you don't want to upload publicly, you can send me a friend request and then send it as a private message.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    TI__Genius 14220 points
    Hi Robin,

    Do you have any update on this?

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    TI__Intellectual 1660 points

    Hi Uttam, 

    I ask the customer, but he didn't response me. 

    Or can you provide a general note that, do we have the other solution, don't need power on from below than 200mv? Or how can we make sure this on circuit design? 

    Regards

    Robin Liu

  • 0 in reply to Robin Liu
    TI__Genius 14220 points
    Hi Robin,

    It could be tackled by using a 0.1uF and a 10uF capacitor on the power supply pin of the DAC. Please make sure the 0.1uF capacitor is placed close to the device pin. In case the power supply is shared with other noisy devices and circuits on the system, it may be a good idea to put a ferrite bead in series with the power supply before the 0.1uF capacitor. So the sequence should be as follows:

    Power Source --> 10uF --> Ferrite bead --> 0.1uF --> DAC Power Pin

    This should solve the problem if the power supply noise is getting coupled conductively. In case it is getting coupled by other means such as electrostatic or electromagnetic, then they should look at the layout and make sure the DAC has other means of isolating this noise, e.g. emi shields etc.

    Hope that answers your question.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    TI__Intellectual 1660 points

    Hi Uttam,

    Re-open this ticket. please refer to the attachment for schematic and waveform capture。

    the waveform is the Vcc. After power-down about 1.2s, then power-up, the issue would happen.

    So how to avoid this?

    Regards

    Robin Liu 

  • 0 in reply to Robin Liu
    TI__Genius 14220 points
    Hi Robin,

    In order to find out the root cause, I would suggest unmounting the DAC and ADC and then check the power supply output. If it's clean, mount them one by one and check the power supply with each condition. This way we will be able to locate the source of this problem.

    Regards,
    Uttam