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[Urgent] Bus holder behavior

Kaka
Guru 24520 points

Hi,

Please let me confirm the following question.

[Question]

What pull-down resister values should we use  for the pin which has bus holder function in order to change the status from "H" to "L" in view of variation of device?

I know that the datasheet has this specification as below.

Regarding to this, we should be mount the pull-down register which can flow the 1.3mA@3.3V.

However. XF pin did not change the status even though mounted this register.  As a result, we could the status by using 1.5kohms (Approximately 2.0mA).

So, I would like to know the best pull-down resistor value which can have a effect of changing the status in view of variation of device.

If you have any questions, please let me know.

Best regards

Kaka

  • 0
    TI__Guru* 84005 points

    Kaka-san

    Please expect delays in closure of your outstanding posts due to the holiday schedule.
    Please clarify the following

    Kato Motoki said:
    However. XF pin did not change the status even though mounted this register.  As a result, we could the status by using 1.5kohms (Approximately 2.0mA).

    What is the condition of testing this? CVDD off?

  • 0 in reply to Mukul Bhatnagar
    Guru 24520 points

    Hi Mukul,

    Thank you for your response in spite of the year-end holiday.

    The test condition is the RTC-only mode,  i.e. The CVDD was powered off.

    If you need more information to think, please let me know.

    Best regards.

    Kaka

  • 0 in reply to Kaka
    TI__Genius 12575 points

    Hello Kaka-san,

      Below are few of the suggestions to try:

      1. Can you lower the resistor value to 750 Ohms and check?

      2. Also is it possible to temporarily short the XF pin to ground and then release: Check whether this pin remains at 'L' or it jumps back to 'H'.

     Please confirm on the above suggestions.

    Regards

     Vasanth 

     

         

  • 0 in reply to Vasantha K
    Guru 24520 points

    Hi Vasantha,


    Thank you for your response.

    I confirmed your request No.2 with using the C5515EVM.

    As a result, when to temporarily short the XF pin to ground and then release,  the XF pin changed the status from "H"  to "L".

    Also I have question for your suggestion No.1. I think that if use 750 ohms pull-down resister for this, the status will be changed because the 1.5k ohms can change the status. And if use the 750 ohms for the pull-down resister of XF pin, the current will be approximately 4mA.

    Would you please explain the reason of 750 ohm pull down resister in logical?

    I would like to know why you chose this value.

    Best regards.

    Kaka

  • 0 in reply to Kaka
    TI__Genius 12575 points

    Hello Kaka-san,

      Thanks for confirming on suggestion #2.

     On Suggestion #1, I had thought that you were not able to change the status to 'L' even with 1.5Kohms. So thats the reason we suggested to try with lower resistor value. sorry about that confusion.

    Will get back to you on the right resistor value. Mean while I have few more questions:

         1.  What is XF used for ?

         2. Is there any other logic on XF pin besides the pull-down resistor.

    Regards

     Vasanth

     

  • 0 in reply to Vasantha K
    Guru 24520 points

    Hi Vasanth,

    Thank you for your reply.  I answered your question in line as below.

    >     1.  What is XF used for ?

    [Kaka]   Customer is used this pin for controlling the mode(PWM - PFMl transfer switch) of DCDC converter(XC9128D45CAR-G).

    >     2. Is there any other logic on XF pin besides the pull-down resistor.

    [Kaka]  There is not any other logic.  

    If you need to confirm their schematics more detail, please tell me your Email address. I can sent you customer's schematics.  I could not attach it to this post because this is NDA information.

    If you have any more question. please let me know.

    Best regards.

    Kaka