TCA9617B: TCA9617B Pull-Up resistor of I2C

Hello Ishiwata-san,

1) "I confirmed I2C Bus Pullup Resistor Calculation of the document, but it was different from the recommended circuit pull-up of the data sheet of TCA9617B."

The I2C Pullup resistor Calculation document isn't wrong here. TCA9617B on B side is a little special though, because you need to drive B side lower than 0.45V in order to drive a signal low from B to A. You just need to make sure you can drive below 0.45V on B side. All I2C devices that follow version 6 standard must generate 0.4V or less when IoL=3mA. This gives you the absolute minimum resistance you are allowed to use (equation 8 of the document you referenced). This means you just need to choose a pull up resistor that is larger than what you calculate using equation 8. You can still use equation 7 to calculate the max pull up resistance you are allowed to use but you will need to use change the rise time to 120ns if you intend to use fast mode plus (1MHz).

2) "I want to pull up the EN pin with VCC, but is there a need for resistance?
     Is there not a need for an external pull-up resistor due to the internal pull-up resistor?"

You don't have to but the internal pull up resistor is a bit weak (100k if I recall correctly), putting an external one will help if your application/end equipment is expected to be somewhere with a lot of electrical noise. 10k should be enough.

3) "Please tell me the recommended value of Decoupling Capacitor for VCCA and VCCB."

0.1uF should be fine.

Thanks,

-Bobby

Hello Bobby-san

Thank you for answering.

1)Please let me ask you a question in addition about I2C Pull-Up.
I want to pull up the A side by 3.3 V and the B side by 5.5 V,
Is it better to use a resistance value slightly higher than the value calculated from equation (8)?

2)It is a pull up of EN, but is it VCCB to pull up?

Best Regards,
Ishiwata