Regulator Design Guidelines; Ferrite Selection Guidelines - Xilinx Virtex-5 RocketIO GTP User Manual

Chapter 10: GTP-to-Board Interface

Regulator Design Guidelines

The selection criteria for the regulator design are:
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Ferrite Selection Guidelines

The selection criteria for the ferrite are:
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Figure 10-11
1. If the current rating of a ferrite is maxed out, the magnetic material of the ferrite body is in saturation, which
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Do not operate the regulator with a V
Keep in mind that the dropout voltage is highly load dependent.
Remember that the regulator stability and performance are only guaranteed. When
using the correct decoupling capacitors (value, ESR, dielectric material) on input,
output, and bypass pins of the regulator.
Strictly follow the layout rules of the regulator data sheet.
Do not max out the output current of the regulator (allow enough headroom under all
operating conditions, especially when it comes to high temperature).
Place, if possible, the regulator close to the filter network.
Place the filter network as close as possible to the analog supply pin that it sources.
Remember that the PSRR of the regulator is output load current and frequency
dependent.
Choose a ferrite with a low DC resistance.
Do not max out the ferrite current rating
Choose a ferrite with a high impedance in a frequency range where you expect or
measure the highest spurs or noise levels.
illustrates the impedance over frequency characteristics of different ferrites.
Figure 10-11: Impedance over Frequency Characteristics of Different Ferrites
impacts its ability to suppress high frequencies.
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that is just slightly over V
IN
(1)
.
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
R
+ V .
OUT DROPOUT
UG196_c10_11_100506