SMARC T335x Carrier Board Hardware Design Guide, Document Revision 1.2
2.2.2.5. LAN Link Activity and Speed LED
The
SMARC
module has three 3.3V open drain outputs to speed
indication and link status LEDs. The 3.3V standby voltage should be used
as LED supply voltage so that the link activity can be viewed during
system standby state. Since LEDs are likely to be integrated into a RJ45
connector with integrated magnetics module, the LED traces need to be
routed away from potential sources of
EMI
noise.
Consider adding a filtering capacitor per LED for extremely noisy
situations. The suggested value for this capacitor is 470pF.