About the amplitude of FEC_TX_CLK(REF_CLK) on i.MX25 FEC

[yuuki]

Dear all,

We use i.MX257 in our system.
And the RMII I/F of i.MX25 is used.

When Drive Strength on the device side is made small, the amplitude of FEC_TX_CLK(REF_CLK) becomes the 4Vpp degree.
When Drive Strength on the device side is made big, the amplitude of FEC_TX_CLK becomes the 5.2Vpp degree.

We want to know the amplitude range that FEC_TX_CLK can allow.
(Min/Max Value)

May I have advice?

Best Regards,
Yuuki

[Yuri]

   It is needed to select drive strength (output impedance of source should match

input impedance of  receiver) properly for high frequency signals to avoid

glitches on signals edges.

Have a great day,
Yuri

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[yuuki]

Dear Yuri-san,

Thank you for your support.

We changed DriveStrength of CLK of EtherPHY.
(This CLK's amplitude  changes from 4Vpp to 5.2Vpp.)

We want to know the amplitude range that FEC_TX_CLK(i.MX's pin) receiving this CLK signal can allow.

Best Regards,
Yuuki

[Yuri · Accepted solution]

  Strictly speaking, over-/under-shoots are not specified for i.MX25.
Nevertheless,  customers can be oriented on the following :

  Overshoot and undershoot conditions (transitions above OVDD and below GND)
on switching pads must be held below 0.6 V, and the duration of the overshoot/undershoot
must not exceed 10% of the system clock cycle. Overshoot/ undershoot must be controlled
through printed circuit board layout, transmission line impedance matching, signal line termination,
or other methods. Non-compliance to this specification may affect device reliability or cause permanent
damage to the device.

Regards,

Yuri.