Texas Instruments TIDA-010046, Руководство по конструкции

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System Overview
15 TIDUES1A – October 2019 – Revised February 2020
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EMC Compliant 10/100-Mbps Ethernet PHY Reference Design With IEEE
802.3at Type-1 ( ≤ 12.95 W) PoE-PD
The purpose of the transformer with a 1:1 ratio is to create galvanic isolation between the cable and the
system. The PHY-side center tap of the transformer should connect through a capacitor to ground,
forming a low pass filter with common-mode choke as
Figure 11 shows. The CMRR cutoff frequency can
be changed by common-mode choke selection and through the adjustment of the capacitor. The isolation
transformer used in this reference design is the HX1198FNL from Pulse Electronics. The key performance
metric affecting the transformer is winding tolerance. Winding tolerances affect amplitude step-up and
step-down from the primary to secondary side of the transformer, and should remain within ±2%.
Figure 11. LAN Magnetics