I forgot to provide 3.3V power to NVCC_ENET

[qumai]

I forgot to provide 3.3V power to NVCC_ENET, but the external RMII interface PHY chip can work normally. After testing, it is found that the power supply of NVCC_ENET is back-filled to it by the MDIO signal from a pull-up (pull-up resistor of 4.7k) to 3.3V, and it is stable at about 2.140V. When I tried to change 4.7K to 2.2K, I found that the voltage of NVCC_ENET increased to 2.42V,

The first question, I would like to ask why the external 3.3V can be fed back to NVCC_ENET through the MDIO signal?

The second question is, can the risk caused by design problems be reduced to zero by reducing the MDIO pull-up resistance without changing the board?

[Yuri]

@qumai 
Hello,

  what i.MX device is used in the case ?

Regards,
Yuri.

[qumai]

MCIMX6Q5EYM10AD

[Yuri]

@qumai 
Hello,

  for i.MX6, in any case, NVCC_ENET must be applied. 
Customers can refer to Table 2-21 (Recommended connections
for unused analog interfaces) of the Hardware Development Guide.
ENET signals are not mentioned there, assuming NVCC_ENET must
be applied. 

http://cache.nxp.com/assets/documents/data/en/user-guides/IMX6DQ6SDLHDG.pdf

Regards,
Yuri.

[qumai]

why the external 3.3V can be fed back to NVCC_ENET through the MDIO signal?

[Yuri]

@qumai 
Hello,

  one of the reasons why all i.MX6 supply voltages should be applied
is leakages avoiding .

Regards,
Yuri.