Specifications

DP83848C , DP83848I
DP83848VYB, DP83848YB
SNLS266E –MAY 2007–REVISED MARCH 2015 www.ti.com
Table 7-4. Magnetics Requirements
PARAMETER TYP UNITS CONDITION
Turn Ratio 1:1 — ±2%
Insertion Loss -1 dB 1-100 MHz
-16 dB 1-30 MHz
Return Loss -12 dB 30-60 MHz
10 dB 60-80 MHz
-30 dB 1-50MHz
Differential to Common Rejection Ratio
-20 dB 50-150 MHz
-35 dB 30 MHz
Crosstalk
-30 dB 60 MHz
Isolation 1,500 Vrms HPOT
7.2.1.5 ESD Protection
Typically, ESD precautions are predominantly in effect when handling the devices or board before being
installed in a system. In those cases, strict handling procedures need be implemented during the
manufacturing process to greatly reduce the occurrences of catastrophic ESD events. After the system is
assembled, internal components are less sensitive from ESD events.
See Section 5.2 for ESD rating.
7.2.2 Detailed Design Procedure
7.2.2.1 MAC 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-Ω 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).
7.2.2.1.1 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.)
7.2.2.1.2 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 cross talk. It is recommended to keep the signal trace lengths as short as possible.
Ideally, keep the traces under 6 inches. Trace length matching, to within 2.0 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.
7.2.2.2 Calculating Impedance
The following equations can be used to calculate the differential impedance of the board. For microstrip
traces, a solid ground plane is needed under the signal traces. The ground plane helps keep the EMI
localized and the trace impedance continuous. Since stripline traces are typically sandwiched between the
ground/supply planes, they have the advantage of lower EMI radiation and less noise coupling. The trade
off of using strip line is lower propagation speed.
72 Application, Implementation, and Layout Copyright © 2007–2015, Texas Instruments Incorporated
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