PMBus multi-slave issue

by Lyzker   Last Updated August 18, 2018 18:25 PM

I have PMBus slave device: A, B, C all running at 400kHz. There is a dongle which connects to a laptop as PMBus master. There is also GUI to display.

Board A, B, C have slave address (7-bit) 0x50, 0x52 and 0x54 respectively; which we use pulled-down on two GPIO pins on the chip to hardware configure the device slave address.

The PMBus communication works fine if we connect master to only one slave either A, B, C. Also, it always works for master to multi-slave A and B. However, multi-slave A and C, multi-slave B and C always have issues. Sometimes, it works (10%) first power up and sometimes (90%) slave address NO_ACK for board C or wrong data after handshake for board A and B. Boards A, B, C are the same board. There is 1K pulled-up on each SDAT and SCLK. Ideally if multi-slave A and B works, multi-slave A and C, B and C should also work fine.

We reduced pulled-up to 300 Ohm and it doesn't work. Is there anything we should be looking at this point?

Please shed some light. Thanks!

Tags : i2c slave smbus pmbus

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