• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 159 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS3823: MR Pin Time Constant

user5163865
Genius 3525 points
Part Number: TPS3823

Hi,

A customer is considering increasing the time constant of the MR pin as part of a response to market problems.

They are planning to change it from 10uF to 20uF.
- Is there any problem if current flows through the internal resistance when the power is turned off?

Looking at the datasheet, I see a 52k ohm resistor, so I don't think there is anything wrong with it.
Please let me know if you have any problems.

Best regards,

Hiroshi

  • 0
    TI__Expert 5200 points

    Hi Hiroshi,

    Thanks for your question! Can you please let me know how much volt they are planning to connect to VDD pin? 

    Best Regards,

    Sila Atalar 

  • 0 in reply to Sila Atalar
    Genius 3525 points

    Sila-san,

    Thank you for your support.

    3.3V is applied to VDD PIN.

    Best regards,
    Hiroshi

  • 0 in reply to user5163865
    TI__Expert 5200 points

    Hi Hiroshi-san,

    Can you please also clarify what is the intention of adding a capacitor on MR?
    -Is it slowing down the reaction time of MR when it's triggered or adding additional time delay when deasserted? 

    Best Regards,

    Sila Atalar 

  • 0 in reply to Sila Atalar
    Genius 3525 points

    Hi Sila-san,

    I apologize for the inconvenience.

    I have confirmed with the customer the reason for adding the capacitor.
    The end user is having malfunctions during use, so connecting 10uF to the MR has improved the situation a bit, but there is still about a 10% failure, so we would like to add 20uF.

    It seems that the details of why connecting a capacitor improves malfunctions are unclear.

    The MR terminal is connected to an external device, and since the details are unknown, this experiment is just a cut and try.

    This problem is caused by an unintended RESET.
    Although there is no clear explanation from the customer, I suspect that noise is getting into the MR terminal.

    Ignoring whether or not it is effective as a troubleshooter, I don't think the 20uF connection will cause any serious problems with this device, but what do you think?

    Best regards,

    Hiroshi

  • 0 in reply to user5163865
    TI__Expert 5200 points

    Hi Hiroshi-san,

    I'll be checking with design team on would 20 uF would harm the device. I want you to know that  I'll get back you when I got an answer from them. 

    Best Regards,

    Sila Atalar

  • 0 in reply to Sila Atalar
    TI__Expert 5200 points

    Hi Hiroshi-san, 

    After I talked with our team to understand if the reverse current on the MR pin may cause any problem on the device and I have feedbacks for you.

    Since the cap is large, when power is turned off, device will see a reverse the current from the cap through the internal pullup resistor, as it seen in the functional block diagram. Our team couldn't see a problem with that.

    But  I want you to know that there is another potential problem here that you should be aware of. If VDD ramps up suddenly by more than 50% of its steady state value, MR will not follow VDD quickly due to the large time constant. And momentarily, MR will be perceived as logic-LOW, since as per the new VDD. This will most likely cause Reset to assert. 

    Best Regards,

    Sila Atalar