P82B715: P82B715 on device A, Device B without P82B715

Dominik Eugster

Part Number: P82B715

Hello

I like to use the P82B715 on a PCB Device A which I design. Device B can be a version without P82B715 and with P82B715. Of course when I implement the P82B715 on both sides, It will work. But what happens if I have some devices on the I2C Bus without a P82B715 driver but the same voltage levels? Is this working and the noise immunity better then without the P82B715 on both sides? I have some sensors over a 5m cable with around 500pF and 50kHz I2C and getting some errors in the ciommunication sometimes. With the P82B715 this errors will be eliminated I hope, but I have still some sensors which I should support and without a P82B715 inmcluded.

Thanks for a reply, Dominik

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 316690 points

I²C is bidirectional. All devices on the bus must be able to pull the voltage down properly.

500 pF is probably not be a problem if the speed is low enough. Howvever, the P82B715 is typically used with very strong pull-up resistors, and your sensor might not have enough drive strength for that. (And using the P82B715 with normal pull-up resistors would be pointless.)