Ethernet Pwr & Power ON Sequence

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1

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?

tks

Mike

2

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

Gerald
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3

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?

Mike

4

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.

Gerald