Data Sheet

Ethernet Controller I210 —Design Considerations
812
• The two load capacitors, crystal component, the Ethernet controller device, and the crystal circuit
traces must all be located on the same side of the circuit board (maximum of one via-to-ground
load capacitor on each XTAL trace).
• Use 27 pF (5% tolerance) 0402 load capacitors.
• Place load capacitor solder pad directly in line with circuit trace (see Figure 12-10, point A).
• Use 50 impedance single-ended microstrip traces for the crystal circuit.
• Route traces so that electro-magnetic fields from XTAL2 do not couple onto XTAL1. Do not route as
differential traces.
• Route XTAL1 and XTAL2 traces to nearest inside corners of crystal pad (see Figure 12-10, point B).
• Ensure that the traces from XTAL1 and XTAL2 are symmetrically routed and that their lengths are
matched.
• The total trace length of XTAL1 or XTAL2 should be less than 750 mils.
Figure 12-10.Recommended Crystal Placement and Layout
12.4 Oscillator Support
The I210 clock input circuit is optimized for use with an external crystal. However, an oscillator can also
be used in place of the crystal with the proper design considerations (see Table 11-17 for detail clock
oscillator specifications):
• The input capacitance introduced by the I210 (approximately 20 pF) is greater than the capacitance
specified by a typical oscillator (approximately 15 pF).
• The input clock jitter from the oscillator can impact the I210 clock and its performance.
Crystal Pad Crystal Pad
Ethernet Controller
XTAL1XTAL2
27pF
0402
27pF
0402
Crystal
“B” “B”
“A”
90 mils
90 mils
Capacitor Capacitor
Less than 660 mils