Specifications

DP83848Q-Q1
SNLS341C –MARCH 2011–REVISED MARCH 2015 www.ti.com
6.2.1.4 Magnetics
The magnetics have a large impact on the PHY performance as well. While several components are listed
below, others may be compatible following the requirements listed in Table 6-4. It is recommended that
the magnetics include both an isolation transformer and an integrated common mode choke to reduce
EMI. When doing the layout, do not run signals under the magnetics. This could cause unwanted noise
crosstalk. Likewise void the planes under discrete magnetics, this will help prevent common mode noise
coupling. To save board space and reduce component count, an RJ-45 with integrated magnetics may be
used.
Table 6-4. Magnetics Requirements
PARAMETER TYP UNIT CONDITION
Turn Ratio 1:1 — ±2%
Insertion Loss –1 dB 1 MHz to 100 MHz
–16 dB 1 MHz to 30 MHz
Return Loss –12 dB 30 MHz to 60 MHz
–10 dB 60 MHz to 80 MHz
–30 dB 1 MHz to 50 MHz
Differential to Common Rejection Ratio
–20 dB 50 MHz to 150 MHz
–35 dB 30 MHz
Crosstalk
–30 dB 60 MHz
Isolation 1500 Vrms HPOT
6.2.2 Detailed Design Procedure
6.2.2.1 1MAC Interface (MII/RMII)
The Media Independent Interface (MII) connects the PHYTER component to the Media Access Controller
(MAC). The MAC may in fact be a discrete device, integrated into a microprocessor, CPU or FPGA. On
the MII signals, the IEEE specification states the bus should be 68 ohm impedance. For space critical
designs, the PHYTER family of products also support Reduced MII (RMII). For additional information on
this mode of operation, refer to the AN-1405 DP83848 Single 10/100 Mb/s Ethernet Transceiver Reduced
Media Independent Interface (RMII) Mode Application Report (SNLA076).
6.2.2.2 Termination Requirement
To reduce digital signal energy, 50-Ω series termination resistors are recommended for all MII output
signals (including RXCLK, TXCLK, and RX Data signals).
6.2.2.3 Recommended Maximum Trace Length
Although RMII and MII are synchronous bus architectures, there are a number of factors limiting signal
trace lengths. With a longer trace, the signal becomes more attenuated at the destination and thus more
susceptible to noise interference. Longer traces also act as antennas, and if run on the surface layer, can
increase EMI radiation. If a long trace is running near and adjacent to a noisy signal, the unwanted signals
could be coupled in as crosstalk. TI recommends keeping the signal trace lengths as short as possible.
Ideally, keep the traces under 6 inches. Trace length matching, to within 2 inches on the MII or RMII bus
is also recommended. Significant differences in the trace lengths can cause data timing issues. As with
any high-speed data signal, good design practices dictate that impedance should be maintained and stubs
should be avoided throughout the entire data path.
66 Application and Implementation Copyright © 2011–2015, Texas Instruments Incorporated
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