Intel 820E manual Distance from Magnetics Module to RJ45

Intel® 820E Chipset

R

Figure 73. Critical Dimensions for Component Placement

		B	A
	Intel®
ICH2	82562ET /	Magnetics	Line
	82562EM	Module	RJ45
EEPROM			crit_dim_comp_plac

Distance	Priority	Guideline
A	1	<1 inch
B	2	<1 inch

2.22.4.4.1. Distance from Magnetics Module to RJ45

Distance ‘A,’ in the previous figure, should be given the highest priority during board layout. The separation between the magnetics module and the RJ45 connector should be kept to less than 1 inch. The following trace characteristics are important and should be observed:

•Differential impedance: The differential impedance should be 100 Ω . The single-ended trace impedance is approximately 50 Ω . However, the differential impedance also can be affected by the spacing between traces.

•Trace symmetry: Differential pairs (e.g., TDP and TDN) should be routed with consistent separation and with exactly the same lengths and physical dimensions (e.g., width).

Caution: Asymmetric and unequal-length traces in the differential pairs contribute to common-mode noise. This can degrade the receive circuit’s performance and contribute to radiated emissions from the transmit circuit. If the Intel 82562ET component must be placed farther than a couple of inches from the RJ45 connector, distance B can be sacrificed. It should be a priority to minimize the total distance between the Intel 82562ET component and RJ-45.

Note: The measured trace impedance for layout designs targeting 100 Ω often yields a lower actual impedance. OEMs should verify the actual trace impedance and adjust their layout accordingly. If the actual impedance is consistently low, a target of 105 Ω –110 Ω should compensate for second-order effects.

Design Guide 117