I2C pull up resistors on a custom esp32 board

[InvertingOpamp]

Hi, I am designing a custom board with special focus on I2C sensors. I have daisy chained I2C 4 pin connectors with shared VCC and GND. I have decided to pull up the SDL and SCL lines on the board. But there are I2C modules which already have SDA and SCL pull ups. Does having extras pull ups on my board affect the I2C communication with such boards? How can I design it so It works with both modules which don't have pull ups and modules that have pull ups.

Thanks!

[-Rudy-]

All the boards that I have seen with pullups use higher value resistors. eg 4k7-10k. This is mostly a maximum value that should be used.

The specification for I2C is the device needs to be able to sink 3 mA. With 3.3 volts supply that would mean the minimum pull resistance would be 1k1. This would mean you could put a few modules on the line and still be within spec.

I normally use a 2k2 resistor for the line and assume that the additional resistors on the modules will not overload the line. I just did a resistance check on a board I am using to develop a product. It has three I2C module plugged into it. With the 2k2 resistors I have soldered in, the three modules bring the resistance down to 1k28 Ohms. Adding one more module brings the resistance down to about 1k1. If I wanted to add more modules I would change my default 2K2, but currently this is as many as devices I expect to use.

[jgustavoam]

Hi,
ESP32 uses 3,3V voltage, so recommended pullup = 3.3K ohms.