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INDUSTRY 4.0/SMART FACTORIES
Figure 2. Example of a PoE circuit. Because PDs must accept a dc operating
voltage of any polarity over their Ethernet inputs according to the IEEE 802.3 PoE specifications, two diode bridges are required in front of the inputs of the PD. Thus, the PD also works with reverse polarity, regardless of the wire pair used.
PD IMPLEMENTATION MADE EASY With the LT4276 from ADI, an LTPoE++-, PoE+-, and PoE-compliant PD controller with an integrated isolated switching regulator exists. It can be operated both for forward and for flyback topologies, and synchronously for power classes from 2W to 90W. Unlike conventional PD controllers of lower power classes, which also have integrated power MOSFETs, the LT4276 offers the option of driving an external MOSFET. Through this, the PD decreases its losses and increases its efficiency. Because the IEEE 802.3 Ethernet specifications
require electrical isolation from the ground connection of the device housing, the
LTC4290/LTC4271 isolated controller chipset is suitable as a PSE. The LTC4271 represents the digital interface to the PSE host on the non-isolated side, whereas the LTC4290 offers the Ethernet interface on the isolated side. The two components are connected by means of a simple Ethernet transmitter. Through this robust PSE chipset design, additional components for generating the isolated power supply can be avoided. An increase in the power and efficiency of the
overall PoE system can be achieved if the two diodes of the full-bridge rectifier on the PD side are replaced by ideal diodes. Therefore, MOSFETs are used and controlled such that they act like typical diodes. Through this, the forward voltage can be drastically lowered due to the low channel resistance (RDS(ON)). With the LT4321 ideal diode bridge controller in combination with the LT4295 PD controller, four MOSFETs can be controlled in a full-bridge configuration (see Figure 3). With PoE, Ethernet devices can be supplied with power at the same time as the actual data
transmission takes place via an RJ45 cable. Analog Devices has developed its own proprietary standard, LTPoE++, that supports powers of up to 90W in parallel to the conventional PoE standards. LTPoE++ offers a robust, end-to-end, high power PoE solution that simplifies the power supply and the design. The new Chronous portfolio is ADI’s portfolio
for innovative Industrial Ethernet products. It includes real-time Ethernet switches, PHYs, and protocol processing products, as well as complete network interface products. The Chronous portfolio was recently expanded with ADI’s release of two new robust Industrial Ethernet PHYs, ADIN1300 (featuring 10Mbps to 1Gbps range) and ADIN1200 (featuring 10Mbps to 100Mbps range). By combining those new PHYs with ADI’s PoE technology, the Chronous portfolio enables best-in-class, system-level solutions for both power and data.
Analog Devices
www.analog.com
Figure 3. Conventional diode rectification vs. driving via a diode bridge controller
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