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Original question:

LP55231: Enable Pin Pull-Up

LP55231: Pullup values - TRIG, INT, EN

Sean Casley
Prodigy 10 points
Part Number: LP55231

I am trying to figure out if 121K ohm resistors are a good choice for pulling up the TRIG, INT, and EN pins on the LP55231. I know section 8.1 of the datasheet recommends using from 120k to 180k "for two devices". What is a good choice for a single device?

Anything above a 10k pullup just seems so weak to me.

Thank you  

  • 0
    TI__Expert 4160 points

    Hi Sean, 

    121Kohm pull-up resistors might be too large. You can refer to the typical single-device application, ground the TRIG pin, and configurate INT pin as NC. As for EN pin, no pull-up is required. 

    Best Regards, 

    Aaron Bing

  • 0 in reply to Aaron Bing
    Prodigy 10 points

    Hi Aaron, 

    Due to the nature of my controller I would like to ensure that the INT, and EN are in known states during start up (I decided to ground the TRIG pin). For this reason I want to include pullup resistors on these pins. I am not concerned about low power and I want to minimize the influence of noise.

    Based on the datasheet I can't find a reason the INT or EN pin could not handle a 10k pullup. The EN pin seems to be high impedance and the INT pin seems to be able to handle up to 3mA. 

    Am I missing something or can the pull-up be in the 10k range? The specification for a 121k is throwing me a little.

    Thank you, 

    Sean

  • 0 in reply to Sean Casley
    TI__Expert 4160 points

    Hi Sean, 

    I will send you an email in response to this issue. 

    Best Regards, 

    Aaron Bing

  • +1 in reply to Sean Casley
    TI__Expert 4160 points

    Hi Sean,

    Quick summary here on the document we found useful to calculate appropriate pull-up/pull-down resistor values:

    Pullup_Pulldown_Resistor_Calculation.pdf

    According to Section #2: Calculating the Pull-up Resistor Range, the calculation on TRIG/INT pins generates a minimum pull-up resistor values of 1.1kohm and a maximum of 990kohm. The typical 120k~180kohm stated on the datasheet is within that range. 

    Best Regards, 

    Aaron Bing