Ethernet Pwr & Power ON Sequence

I did do a search first on this subject and did not come up with anything.

The BBB the LAN8710 PHY is powered by the VDD_3V3B rail. The VDD_3V3B rail comes from a LDO sourced by SYS_5V and enabled by the PMCI VDD_3V3AUX. My questions are:

  1. Why not power the PHY directly off of the PMIC VDD_3V3AUX?
    If OK use a analog switch like TPS27082 to EN power on PHY sequence?

  2. Is the VDD_3V3B LDO for power-ON-sequence the PHY after the PMIC has already gone through power sequence?



Not enough current.
VDD_3V3AUX comes on at the wrong time in the sequence
The 3V3B rail is for extra current.


Thanks Gerald,

Your reply is what I was suspecting.

What is interesting the regular BB Rev A6A (not the BB Black) powers the PHY from PMIC LDO4. I’m curious if they have had any issues?


Look at he rest of the PMIC. We had to move the regulators around due to the 1.5V rail requirement for DDR3. We lost a higher current LDO as a result. Also note the different versions of the PMIC used between the two boards.