EDNE April 2012 - (Page 29)

ground but instead remain open for a 10BaseT Ethernet system. Because IEEE 802.3 does not strictly allow for common-mode protection on the primary side of the coupling transformer for cable-discharge-event-protection reasons, the thyristor-surge-protection devices usually do not connect to ground. Therefore, most Ethernet approaches depend on the isolation rating of the coupling transformer for longitudinal/common-mode protection on the line side, whereas the tertiary position on the secondary side of the coupling transformer may connect to the Ethernet line driver’s ground reference. TVS3, a 2.5V TVS-diode array, provides tertiary protection on the chip side of the coupling transformer. This approach complies with the surge and power-fault requirements of GR 1089-Core, Issue 6, for intrabuilding and interbuilding POE. You can substitute a 0.3A PTC device for the fuses for compliance with ITU K.20/21 enhanced and basic, which contain coordination clauses for 10BaseT Ethernet. However, for 100 and 1000BaseT, you would use a pair of appropriately sized, precision, 1% resistors to force coordination between the secondary and the primary protectors. Figure 5 shows both data-pair protection and PD centertap power-connection protection that comply with both Mode A and Mode B POE power for the PD end of the system. Both PD Mode A and Mode B POE are protected by a diode bridge and a 1000W TVS device. More robust, 1500 and 3000W, approaches are also available for harsher surge environments, such as those that regulatory standards ITU K.20 Enhanced or GR-1089 Port Type 5 describe. As the power POE systems deliver has increased, developers are installing Ethernet equipment in areas that expose it to increased hazards from lightning-induced overvoltages and 50- to 60-Hz power-line faults. Judicious use of bidirectional surge-protection devices, TVS diodes, fuses, and PTC devices can help ensure reliable operation despite these hazards.EDN auThors’ BioGraPhiEs Phillip Havens is the technical-marketing and application manager at Littelfuse and brings a wide range of electronics engineering expertise. He earned both bachelor’s and master’s degrees in electrical engineering from Louisiana Tech University (Ruston, LA), is a licensed professional engineer, and interfaces extensively with the technical teams of many leading electronics manufacturers to develop circuit protection for specialized applications. Havens represents Littelfuse at electronics-safety, circuit-protection, and telecom-related industry associations and helps define, direct, and support the company’s silicon-based-protection-product lines. You can reach him at phavens@littelfuse.com. Chad Marak is a product-marketing manager in the semiconductor-business unit of Littelfuse Inc. His responsibilities include providing strategic direction for the growth of the TVS-diode-array product line and managing the North America field-applicationengineering team. Marak received a bachelor’s degree in electrical engineering from Texas A&M University (College Station, TX) and a master’s degree in electrical engineering from Santa Clara University (Santa Clara, CA). He has been in the semiconductor industry for 10 years and holds four US patents. You can reach him at cmarak@littelfuse.com. www.edn-europe.com International Conference and Exhibition for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management Nuremberg, 8 – 10 May 2012 Powerful? …then you are right here! The marketplace for developers and innovators. Future starts here! www.pcim-europe.com APRIL 2012 | EDN EUROPE 29 http://www.pcim-europe.com http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE April 2012

Cover
Contents
International Rectifier
Contents
RS Components
Masthead
Comment
International Rectifier
Pulse
Analog Devices
FTDI
Digikey
Mouser
Baker's best
Digikey
Test & Measurement
Agilent Technologies
Digikey
Protect POE systems
Hirose
Coilcraft
Mesago
Cover Story
Digikey
Signal Integrity
RS Components insert
Balancing GBWP and quiescent current
Noise wars
Design Idea
Product Roundup
Tales from the cube

EDNE April 2012