Value of the IPMB pull-up resistors

Dear CERN IPMC team,

We are facing some issues when connecting 3 AMCs to the IPMB bus using the CERN IPMC. Our AMCs are not able to bring the signal to an “reasonable” low level (it stays above 1V). If we connect only 2 of them, the low level is a bit high but not enough to disturb the communication.

What is the value used for the pull-up resistors in the IPMB lines of the CERN IPMC?

Thank you,


Hi Thiago,

Sorry for my late reply. What is the status of this issue?

The pull-ups of the IPMB-L bus are already installed on the mezzanine card with a value of 4.7kOhms. Do you have additional one on your carrier? In addition, do you well connected the bus to i2c buffers?


Hi, Julian.

This issue is closed. The problem was solved by changing the I2C buffers by different ones (PCA9306 was replaced by LTC4300).

By the way, one of the questions was if the resistors on the IPMC were the expected ones. With the picture of the schematic you sent me by email, I was able to get the identification of the resistors and find them on the card. With that, I was able to prove that the resistors soldered in the IPMC were correct (4k7).

Thank you,