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P82B96: Capacitor between bus line and GND is required?

Hisao Uchikoshi
Genius 13510 points
Part Number: P82B96

Hi Experts,

My customer is encountering an issue. VOL on Sx/Sy is defined as 1V(max) while MCU VIL(max) is around 0.7V.

To correspond with this, customer is trying to raise the pull up resister within the max tr which is 1000ns(Standard mode). Looking at the datasheet, there is a capacitor C2 between bus line and GND. In order to use large pull-up resister, customer wants to remove this capacitor C2. 

Why is this C2 existing?  Can we remove it? Furthermore, are there any workaround for this issue without modifying the schematics?

Regards,

Uchikoshi

  • +1
    TI__Mastermind 49040 points

    Hi Uchikoshi-san,

    Those capacitors are actually parasitic caps meant to symbolize the capacitive loading on the bus. Since I2C spec's a cap limit, we typically don't recommend adding capacitance on an I2C bus without good reason. Yes, I would recommend removing it. 

    That offset voltage on that side was designed to allow for the device to redrive the I2C signal while maintaining Bi-directionality. Changing the pull up resistor will help but you'll likely see diminishing returns. You may need to place another I2C redriver infront of it if you need to lower the VoL further.

    -Bobby