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PCM1772: Recommended pull down and pull up resister when I don't use SPI ctrl

Kazuki Kuramochi
Genius 9400 points
Part Number: PCM1772

Hello expert,

I have question for PCM1772.
I had discussed about PCM1772's pin termination when they don't use SPI communication on this thread.
In this thread, I got the answer that is just need to connect to VCC or GND.
Then, is there any recommended pull-up and down resistor value?

I'm looking for hearing back from you.


Best regards,
Kazuki Kuramochi

  • TI__Mastermind 23960 points

    Hello Kazuki,

    If there is no specific recommendation in datasheet regarding the value of pullup or pull downs, Usually I would go by 10k resistors , but  for pins like SCL and SDA , I would use  smaller pull up. 

    Regards,

    Arash

  • in reply to Arash Loloee
    TI__Genius 9400 points

    Hello Arash,

    I understand and suggest to use 10k or smaller for pull-up and down.


    Thank you and best regards,
    Kazuki Kuramochi

  • in reply to Kazuki Kuramochi
    TI__Genius 9400 points

    Hi Arash,

    We selected bull-up and down resistor as MC/MD=4.7kohm and /MS =10kohm.
    Is it acceptable from your side?

    Also, We have additional questions.
    Would you provide answer for below questions?

    1. Why you recommend to use smaller resistor for Data and Clock line than other line?
    2. Is there minimum recommended resistor value of pull-up/down resistor?
    3. Is there any impact for power consumption when we use smaller pull-up/down resistor?

    Thank you and best regards,
    Kazuki Kuramochi

  • in reply to Kazuki Kuramochi
    TI__Mastermind 23960 points

    Hello , 

    Usually these resistors can range from 2k to 10k.  In general, once a node that is connected to PU goes low,  it will draw some tiny current from the supply that is connected to,  and this current increases as the resistor gets smaller. You can take a look at this link (  rheingoldheavy.com/.../  ), although I do not guarantee the correctness of  information it provides, but it can be a good starting point to find the answer to your questions.

    I hope that answers your questions . I'll close the ticket for now.

    Regards,

    Arash

  • in reply to Arash Loloee
    TI__Genius 9400 points

    Hello Arash,

    Would you directly answer my questions?
    For the recommended pull-up/down resistor, you suggested to use smaller resistor on clock and data line against other lines.
    Would you tell me why you suggested to use different resister only for clock and data line?

    Sorry for forgetting it but I have discussed with recommend pull-up/pull-down resistor in this thread.
    In this thread, other TIer suggested to use 10k-100k resistor but you suggested smaller resistor.
    Why is there this difference?

    For quiescent current, you may attached link on URL but I cannot found it.
    I think all pin is input pin so resistor difference don't cause particular increasing of quiescent current against device shutdown mode's Iq(5uA typ).
    Is this understanding correct?


    Best regards,
    Kazuki Kuramochi

  • in reply to Kazuki Kuramochi
    TI__Mastermind 23960 points

    Hello, There is an article that explains how to select the pull up resistors for I2C, you can read it in SLVA689–February 2015 ,      I2C Bus Pullup Resistor Calculation. This is a TI application note and shows detail calculations.

    Regarding the quiescent current your understanding is right, it is  not matter much if it is input pins.

    Regards,

    Arash