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TPD12S521: Pull-ups

Nate Gil
Prodigy 210 points
Part Number: TPD12S521

Tool/software:

I'd like to use TPD12S521 with a RaspberryPi CM5 module, but the module has internal pull-ups:

CEC:27K
SCL/SDA: 1K8
HOTPLUG: 100K PULLDOWN

TPD12S521 reference design shows 1K7 on the connector side, would it be OK to change them to something like 10k?

  • +1
    TI__Mastermind 32501 points

    Hi Nate,

    The issue with using a 10k resistor will be that when you connect a long cable to your port, you will not have sufficient resistance to pull the signal high with a large capacitance.

    If you know that you will only use relatively short HDMI cables, you can reduce the pull-up resistor, but if you want maximum support for long cables, then I suggest that you do not change it.

    You can refer to the NXP I2C Spec:  https://www.nxp.com/docs/en/user-guide/UM10204.pdf to calculate the resistor pull-up for the I2C bus.  

    I believe that the 1.8k resistor was selected to work with cables between 0.5m and 10m, but that board was designed more than 10 years ago, so I am not certain.

    Regards,

    Chuck

  • 0 in reply to Chuck Branch
    Prodigy 210 points

    I see.

    Having 2 sets of 1k8 in parallel (the ones of the module and the ones after the TPD12S521 part would result in a very very strong pull-up. I guess I'll have to find a different protection solution.