Texas Instruments TIDA-010046, Design Manual

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XI
(pin 23)
R
1
XO
(pin 22)
C
L2
C
L1
System Overview
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18 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
Figure 14. Crystal Oscillator Circuit
Table 6. Crystal Specification - 25 MHz
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Frequency 25 MHz
Frequency tolerance
Including operational temperature, aging and other
factors
–50 50 ppm
Load capacitance 15 40 pF
ESR 50
Ω
2.4.10 Electrical Transient Immunity
2.4.10.1 Electrical Transient Immunity for PoE
For electrical transient immunity for PoE, see the Electrical Transient Immunity for Power-Over-Ethernet
application report.
2.4.10.2 Electrical Transient Immunity for Ethernet PHY
The network or Medium Dependent Interface (MDI) connection via transmit (TD+ and TD–) and receive
(RD+ and RD–) is ESD protected. This reference design uses a shielded RJ45 connector without an
internal isolation transformer. RJ45 is the standard cable used for all the Ethernet and LAN applications.
An external isolation transformer is interfaced. The TIDA-010046 design uses the HX1198FNL transformer
from Pulse Electronics. The device is a 1:1 transformer with an isolation of 1.5 kV
RMS
(for 60 seconds).
Based on the application, it may be necessary to connect a common-mode choke along with the isolation
transformer. The HX1198FNL device has an integrated common-mode transformer. The network or MDI
connection is through the transmit (TX+ and TX–) and receive (RX+ and RX–) differential pair terminals.
The transmit and receive terminals connect to a termination network, then to a 1:1 magnetic transformer,
then to ESD protection devices and an RJ45 connector.
This reference design uses the ESDS312 as ESD protection diodes in between the isolation transformer
and Ethernet PHY. The ESDS312 devices are unidirectional TVS ESD protection diode arrays for
Ethernet, USB and general purpose data line surge protection up to 25 A (8/20 µs) . The ESDS312
devices are rated to dissipate ESD strikes at the maximum level specified in the IEC 61000-4-2
international standard (Level 4). The devices features a 4.5-pF IO capacitance per channel making it ideal
for protecting high-speed interfaces such as 10/100/1000 Mbps Ethernet. Another reason for using
ESDS312 is its low surge clamping voltage 6.5 V at 25-A IPP.