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DAC082S085: Wake up time issue

NAOKI AOYAMA
Guru 11215 points
Part Number: DAC082S085
Other Parts Discussed in Thread: DAC128S085EVM

Hello,

Our customer use the DAC082S085.

The customer use power down mode.

When the customer exit power down mode, there is tWU issue.

I attach the scope shot of issue.

DAC082S085_delay.pdf

It is mentioned the tWU is 6us typ @VA=3V on the datasheet.

When the customer exit power down mode after 8sec from set in power down mode,

the tWU is 4ms.

Do you have any idea what cause it?

Best Regards,

Naoki Aoyama

  • 0
    TI__Genius 14220 points
    Hi Naoki,

    Thank you for your query. While I am checking the details with the design team, could you please share the schematics? If you don't want to share it on the public forum, you can send that as a private message to me.

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    Thank you for your reply.
    I will ask the customer to send the schematics.

    Regards,
    Naoki Aoyama
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    Sorry, the customer could not give us the schematics, because it is made by end user.
    I only had information that the VOUTA, VOUTB connect to an input of buffer amp directly.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    I have not been able to get an answer from the team till now due to the holidays. I will get back with an answer soon. Thank you for your patience.

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

    The design team doesn't have any prior knowledge of this type of an issue. This being an old part, we would start with the system to see any root cause. Could you please let me know if there is any other activity/event happening in the system when the DAC is powered up after 8 sec? Do you see any such behavior between 1 sec and 8 sec, or it happens only after 8 sec of power down?

    As this particular part doesn't have an EVM, I am planning to test this behavior with the EVM of same family DAC128S085EVM and let you know about my findings. I will try to come back by end of this week.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    Thank you for your reply and investigation.
    I will check the system of the customer.

    Regards,
    Naoki Aoyama
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    I checked the customer.
    There is no activity/event happening in the system.

    There is new information.
    The customer have evaluated DAC under condition with variable temperature.
    The scope shot that I attached before, it is a result of evaluate at Ta=50 degree.
    When ambient temperature is 25 degree, the wake up time is about 50usec.
    There may be correlation between the wake up time and temperature.

    There is no issue when the duration of power down mode is less than 1sec,
    even if the temperature is 50 degree.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    Is it possible to check whether the power-up delay happens at 25oC as well with 8 sec power down? This condition is not part of the datasheet specs - so, I am sure this was never tested at different temperatures. Does the customer have a problem with the delayed power-up?

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    The customer already checked the power-up delay at 25oC with 8sec power down.
    It is between 50usec and 60usec.
    When the duration of the power down is less than 1 sec, it is in spec.

    The customer does not have a problem.
    The customer want to know the root cause of the power-up delay.
    If it is normal behavior, the customer consider it and use it.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    I couldn't get a very definitive answer from the design team as this is an old part. However, what I got to know from them is that sometimes the internal biasing circuits have temperature dependence and there is a possibility that this is slowing down the rampup when operated at a higher temperature. Unfortunately, this spec is not characterized for this device. But I would say that there doesn't seem to be anything wrong with this device - so, the customer can go ahead and use this. I will try to see if we can incorporate this spec in the future designs.

    Hope that answers your question.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    Thank you for your reply.
    Could you try to reproduce this behavior with the DAC128S085EVM?

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    My apologies for replying late. I am trying to test your condition on the DAC128S085EVM. However, due to the some resource constraint on thermal chamber, this is going to take some time. I will try my best to complete it this week. But in case I am not able to do, I should be able to do it only in the week of 23rd as I will be on travel next week. Thank you for being patient.

    Please let me know if that works for you.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hello Uttam,

    Thank you for your support.
    Even if it at room temperature, it occur delay with the duration of the shut down more than 8sec.
    I thought it does not need a thermal chamber.
    I will wait for your test.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    I am a bit confused now. You mentioned that this occurs only with elevated temperature. I will anyway test with the other EVM and let you know.

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

    I couldn't manage to test the scenario on the EVM before I could start for a week's travel. Could you please confirm again whether the condition occured with elevated temperature of not?

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    The delay time is form 50us to 60us at room temperature and 4ms at 50 degree.
    It may be relation on temperature.
    (The customer use this DAC at VCC=3V. )

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    Thanks for the confirmation. Due to my travel this week, I will be able to test this out on the EVM next week. I will let you know about my findings. Thanks a lot for the patience.

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

    I was unable to arrange a thermal chamber this week for the test. I should be able to do this by early next week.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    Thank you for your a lot of supports.
    I will wait for your investigation.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    I have not been able to arrange the thermal chamber till now. My apologies for the delay. I am trying to finish it at the earliest. Please give a a couple of more days. I will get back with the results.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    Thank you for your support.
    Is there any update?

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    My apologies for the delay. I have not yet been able to arrange the chamber yet. My lab team has assured it by MO this week. I hope to complete the test for you. Thanks a lot for the patience.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    I see.
    I will tell the customer to wait a little more.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 14220 points
    Hi Naoki,

    First of all my apologies for this long delay in resolving this issue. I finally managed to get a thermal chamber and reproduced your use case. What you are observing is repeatable on DAC128S085EVM that is from the same family of devices and I observed that the wake-up time is dependent on temperature.

    Hope that clarifies. I am closing the thread. Please let me know in case you need any support in future.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Guru 11215 points
    Hi Uttam,

    Thank you for your investigation.
    I will feedback the customer this information.

    Thank you very much.

    Naoki Aoyama