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| Classification (Class 0-3) Interface Circuit Application PoE/VoIP Device DPA423G Power Output 6.49 W Input Voltage 36-57 VDC Output Voltage 3.3 V Topology Flyback Design Idea DI-88 (R) DPA-Switch PoE Detection and Design Highlights * * * * Simple interface for Power Over Ethernet (PoE) Powered Devices (PDs) Includes PoE detection and classification circuits for all classes (0, 1, 2 and 3) Compliance to IEEE802.3af PoE standards verified by University of New Hampshire Interopability Consortium (UNH-IOC)* Includes under voltage lockout (42 VDC on, 34 VDC off) Classification occurs as the input voltages rises from 14.5 to 20.5 VDC. The sending device determines the class of the PD by monitoring the amount of current drawn by the PD during this phase. For classes 1, 2 and 3, the classification current (ICL), is programmed by resistor R34, as per the table. Class 0 1 2 3 POUT (min) W 0.44 0.44 3.84 6.49 POUT (max) W 12.95 3.84 6.49 12.95 ICL (min) mA 0.5 9 17 26 ICL (max) mA 4 12 20 30 R34 Ohms 133 69.8 45.3 PoE Detection and Classification PoE is becoming widely adopted for networking and VoIP telecom applications. A typical PD solution is shown in Figure 1 and has a PoE interface circuit and a DPA-Switch DC-DC converter block (see EPR-68 for full details of operation of the DC-DC converter). The PoE specification requires the PD to implement three functions: detection, classification and pass-switch connection. Detection occurs as the input voltages rises from 2.5 to 10 VDC. Resistor R31 within the PD presents the detection impedance to the PSE. Ethernet (RJ-45) D101 Connector DL4002 (1,2) PoE Interface L1 10 H 1A Components R32, R33, R34, R35, Q31, Q32, Q33, Q34, VR31 and U31 are not installed for Class 0 applications, and the classification current is programmed by R31 (24.9 k). Operation Resistor R31 provides the detection impedance. In order to allow correct operation over the detection voltage range, Zener diode C4 1000 pF R7 1500 V 10 k D1 SL42 C7 330 F 6V C8 330 F 6V L2 1 H, 2 A C9 330 F 6V C10 1 F J2-1 10 V 3.3 V, 2 A 1 9,10 + DL4002 D102 D103 DL4002 (4,5) R31 24.9 k 1% VR31 11 V R36 51 k R4 1 M 1% R5 649 k 1% VR3 SMAJ 150A 2 6,7 4 J2-2 RTN D2 BAV21 C11 1 F 50 V MMBTAO6L R32 100 k Q32 3 5 C1 1.5 F 100 V C2 1.5 F 100 V R11 1 k R10 75 R12 34 k 1% MMBTAO6L DL4002 D104 D105 DL4002 (3,6) MMBTAO6L Q31 R33 2 k 1% VR32 27 V D R21 R23 DPA-Switch 174 k 10 k 1% U1 DPA423G Q20 L MMBTS R22 3906 10 k CONTROL C U2 PC357 N1TA LMV431A1M D107 DL4002 (7,8) U31 1% R34 69.8 1% MMST3904 DL4002 D106 R37 220 k R35 100 k Q34 VR33 15 V Q35 100 V 0.250 m Q33 S X F C5 0.1 F R6 8.66 k 1% R9 51 U3 CAT431L C13 0.1 F C6 22 F 10 V C12 0.33 F R13 20.0 k 1% PI-4042-111005 DL4002 D108 Figure 1. PoE Interface Circuit - Class 2. *UNH-IOC test reports are available on the PI website www.powerint.com/poe DI-88 November 2005 www.powerint.com DI-88 VR31 inhibits the classification circuit at input voltages below 11 V. Components Q32, Q31 and R32 form a 350 A bias current source programmed by resistor R33 working in conjunction with the base-emitter voltage of Q31. Transistor Q33 forms the classification current source programmed by resistor R34 working in conjunction with the 1.24 V voltage reference U31. Transistor Q34 disables the classification current source when Zener diode VR32 conducts (when the input voltage exceeds approximately 28 V). of the classification circuit to approximately 20 mW at high input line (57 VDC) plus detection resistor (R31) dissipation of 130 mW. 14 Class 1 Key Design Points * * * For Class 0, remove components VR31, R32, R33, R34, R35, Q31, Q32, Q33, Q34 and U31. R34 values: Class 1, R34 = 133 ; Class 2, R34 = 68.9 ; Class 3, R34 = 45.3 . It is possible to use either bipolar transistor or MOSFET pass-switches (Q35). A bipolar transistor is less expensive, but a MOSFET gives higher pass-switch efficiency. See design idea (DI-70) for details. The bias current source (Q31) is used to allow the classification current source to be turned-off for minimal power loss once input voltage exceeds 28 VDC. This limits the dissipation PI-4043-080905 Current (mA) 12 Classification Voltage Range Class 1 Max 10 Class 1 Min 8 10 12 14 16 18 20 22 * Voltage (V) Figure 3. Classification Current (Class 1: R34 = 133 ). PI-4045-111005 0.80 Class 1 Class 2 Class 3 Detect Min Detect Max Detection Voltage Range Class 2 Class 3 0.60 30 Class 3 Max Current (mA) 23.75 k Current (mA) 26 22 18 Classification Voltage Range Class 3 Min 0.40 Class 2 Max 0.20 26.5 k Class 2 Min 0.00 0 2 4 6 8 10 12 14 10 12 14 16 18 20 22 Voltage (V) Figure 2. Detection Impedance V-I Curve. For the latest updates, visit www.powerint.com Voltage (V) Figure 4. Classification Current (Classes 2 & 3: R34 = 69.8 and R34 = 45.3 ). Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (transformer construction and circuits external to the products) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at www.powerint.com. Power Integrations grants its customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm. The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, EcoSmart, Clampless, E-Shield, Filterfuse, PI Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. (c)Copyright 2005, Power Integrations, Inc. Power Integrations MAIN PHONE NUMBER +1 408-414-9200 C 11/05 5245 Hellyer Avenue APPLICATIONS FAX +1 408-414-9760 San Jose, California 95138 For a complete listing of worldwide sales offices, please visit www.powerint.com APPLICATIONS HOTLINE +1 408-414-9660 www.powerint.com PI-4044-111005 |
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