Other Parts Discussed in Thread: DP83869HM
Tool/software:
The following FAQ applies to the DP83869HM and all versions of the DP83867: E/IS/CS/IR/CR
The Analog Supply pins (VDDA2P5 & VDDA1P8) power the MDI portion (connector side) of the PHY. Recently it was found that the MDI side can back power the VDDA_2P5 pin.
Figure 1 - MDI Portion of the DP83867 PHY
Board A is connected to Board B via an ethernet cable. Board A is powered on and configured into a forced speed mode (Auto-negotiation disabled), and Board B is completely powered off. In forced mode, Board A will begin transmitting data, regardless of link status. On Board B, these signals are received on the MDI pins of the DP8367 and 0.8V can be seen coming out of the VDDA_2P5 pin.
Note: More information about Forced Mode can be found here.
Conclusions:
- This will not damage the DP8386x PHY and will not result in any functional issues, from the PHYs perspective
- On a System level, extra care must be taken to ensure components connected to the DP8386x's VDDA_2P5 pin can tolerate the potential 0.8V back-powering voltage from this specific use-case
- This is inherent to the design of the DP83867 PHY and cannot be adjusted with any register configuration.
-Regards,
Alvaro