i.MX8M mini ENET MDC MDIO Voltage

[MohanadRabea]

Hello,

    According i.MX8M Mini Datasheet; NVCC_ENET supports 1.8V/2.5V/3.3V IO voltage.
And according to Ethernet PHY (AR8031) used in i.MX8M Mini EVK board, MDC, MDIO and nRST pins are 2.5V (3.3V tolerant) and in EVK ENET IO (NVCC_ENET) the voltage is set to 1.8V, and voltage translators have been used for MDC, MDIO and nRST pins.

Since we are integrating ethernet PHY on the same board as the CPU, we would remove the drivers (NC7WV16) as they're not needed anymore, (Please confirm that with me), but what about the voltage translators?

We want to avoid Voltage Translators on MDC, MDIO and nRST pins with the same Ethernet PHY in our Custom design.

So, the questions are:
A) Is the best way being to set AR8031 as well as NVCC_ENET to 3.3v, then we can remove NTS0102(for MDIO and MDC pins) and 74AVC8T245PW (for nRST pin) and connect the pins directly between CPU and ETH PHY?

B) Or we could leave NVCC_ENET and AR8031 set to run at 1.8v IO but keep the voltage translators, i.e. NTS0102(for MDIO and MDC pins) and 74AVC2T245GU (for nRST pin) 
Note: 74AVC2T245GU and 74AVC8T245PW are the same but with different channels.

C) If we keep running NVCC_ENET and AR8031 at 1.8v, what would be the consequences of connecting MDIO, MDC and nRST pins without voltage translation chips in between CPU and AR8031??
    -Would 2.5v MDIO and MDC pins from AR8031 cause non-stable operation or permanent damage to the CPU ENET_MDIO and ENET_MDC pins in extreme cases? or would it work normally? (I doubt...).
    -Same question goes for nRST and noting that it's pulled up to 3.3v.

Best Regards,

Mohanad.

[JosephAtNXP]

Hi,

Thank you for your interest in NXP Semiconductor products,

Best option is B, RGMII support for 3.3V operation has been removed, even though the power domains support it, the ENET module does not and it's recommended to stick at 1.8V operation.

So the power domain would be set at 1.8V, the PHY could work at 1.8V but according to a datasheet that I have, the DC characteristics of MDIO are minimum 2.4V, so add the level translators and remove the drivers.

Regards