AVAILAB LE Maxim > App Notes > Hot-Swap and Power Switching Circuits Keywords: Powered Device, PD, Power over Ethernet, PoE, IEEE 802.3af, IEEE 802.3at, Class 2 PD, Class 3 PD, IP Phones, IP Camera, Security Camera, WAP, Wireless Access Point, Point of Sales, POS. Dec 21, 2010 APPLICATION NOTE 4940 High-Performance Class 2 Powered Device (PD) is Customizable for Class 3 Designs Abstract: This reference design is for a highly efficient, flyback 3.3V and 5V Class 2 powered device (PD). The design features the MAX5969B as its controller. The design also uses the MAX5974A, which controls current-mode PWM converters and provides frequency foldback for PoE applications. Using these devices, this reference design is IEEE® 802.3af/at compliant, and a high-performance, compact, and cost efficient solution for a Class 2 PD. The design can also be customized to 3.3V/2A and 5V/1A Class 3 PD. General Description This reference design is for a highly efficient, flyback 3.3V and 5V Class 2 powered device (PD) that is IEEE 802.3af/at complaint and cost-effective. The reference design can be customized to a 3.3V/2A and 5V/1A Class 3 PD. The design features the MAX5969B and MAX5974A. The MAX5969B controller is fully compliant with the IEEE 802.3af/at standard in a power-over-Ethernet (PoE) system. The device can also get power from a wall adapter (WAD). The MAX5974A provides both control for wide-input-voltage, active-clamped, inductive feedback, current-mode PWM converters and frequency foldback for PoE applications. Using these devices, this reference design is IEEE 802.3af/at compliant. It is also a high-performance, compact, and cost-effective solution for a Class 2 PD or a Class 3 PD. Specifications: The 3.3V/1A, 5V/0.8A PD is designed to meet the following specifications: Input voltage: 36V to 57V WAD input voltage: 36V up to 57V (note: the voltage can be 10V to 57V with a different transformer.) V OUT1 : 3.3V/1A V OUT2 : 5V/0.8A Output ripples: ±2% Load transient V P-P : ±3% (50% step-load) Line and load regulation: ±2% Total efficiency with load of 1A at 3.3V, 0.8A at 5V, and 48V input: 84.5% (including input LAN transformer and diode bridge). Top view of ofthe thereference referencedesign. design. Top view Bottom view of ofthe thereference referencedesign. design. Bo ttom view Page 1 of 4 POUT = 0.8W _5V POUT = 3. 78W_5V POUT = 7.4W _5V LINE REGULATION vs. INPUT VOLTAGE 3.420 3.3V LINE REGULATION (%) 5.150 5V LINE REGULATION (%) POUT = 0.8W _3.3V POUT = 3. 78W_3.3V POUT = 7.4W _3.3V LINE REGULATION vs. INPUT VOLTAGE 5.100 5.050 5.000 4.950 4.900 3.400 3.380 3.360 3.340 3.320 3.300 3.280 3.260 3.240 4.850 30.00 35.00 40.00 45.00 50.00 55.00 3.220 30.00 60.00 35.00 40.00 INPUT VOLTAGE (V) EFFICIENCY vs. OUTPUT CURRENT 55.00 60.00 90.00 80.00 80.00 70.00 60.00 EFFICIENCY (%) EFFICIENCY (%) 50.00 EFFICIENCY vs. OUTPUT CURRENT 90.00 50.00 40.00 30.00 20.00 10.00 0.00 0.000 45.00 INPUT VOLTAGE (V) 0.100 0.200 0.300 0.400 0.500 70.00 60.00 50.00 40.00 30.00 36V_3.3V AT 0.1A_5V AT 0A-0.8A 20.00 36V_3.3V AT 1A_5V AT 0A-0.8A 10.00 0.600 0.700 5V OUTPUT CURRENT (A) 0.800 0.900 0.00 0.000 36V_3.3V AT 0A-1A_5V AT 0.08A 36V_3.3V AT 0A-1A_5V AT 0.8A 0.200 0.400 0.600 0.800 1.000 1.200 3.3V OUTPUT CURRENT (A) Transient Response at 36V Input Voltage VIN = 36V, I OUT1 = 1A, I OUT2 = 0.4A–0.8A–0.4A Ch1: 100mV/div, 5V output voltage Ch2: 100mV/div, 3.3V output voltage Ch4: 0.5A/div, output current Time base: 400µs/div Page 2 of 4 3 T1 V+ NO-OPTO SOLUTION V+ R13 R41 4 1 R38 C1 3 J1 3 V+ AC AC V- C8 2 R11 VC GND C26 + C9 8 R14 1 FB VDD 9 D6 RTN C6 4 R8 N2 GND 3.3V 1 10 C5 V- PG R7 R9 D7 C4 V+ AC 1 1 13 5 6 7 8 N3 SS DT DCLMP EN C12 RTN C34 U2 R6 C10 + VC AUXDRV N1 GND 12 C V- AC 14 C3 D2 15 16 3 V- C14 2 DITHER/SYNC NDRV R19 11 4 3 2 1 4 G2 18 17 G1 C D12 VSS D11 DATA OUT TX4-P8 Y2 TX4+P7 Y1 TX3-P5 20 TX3+P4 19 TX2-P6 C11 R23 D 5V 3 C25 D3 2 22 21 DATA & POWER IN TX2+P3 D5 7 R2 L1 R3 D1 TD1+ TC1 TD1VC1 TD2+ TC2 TD2VC2 TD3+ TC3 TD3VC3 TD4+ CT TD4VC4 TX1-P2 D4 D10 D 11 12 2 10 13 4 6 5 14 3 1 2 15 8 7 9 16 2 J4 J3 R12 6 4 Vin C2 G R5 AUX R20 V+ TX1+P1 4 1 2 2 1 2 1 R17 MAX5974A R15 3 PGND RT 10 RTN VDD R10 C16 B 1 R1 2 3 4 C27 CLS DET 2EC N.C. PG N.C. WAD VSS RTN 10 C24 R25 RTN R21 R18 B C18 CLS RTN 9 PG C31 8 + C7 C13 C17 7 6 Vin EP 5 VDD EP Vin FB CSSC C15 L2 U1 MAX5969B SGND R26 9 8 FB 7 RTN CS FFB COMP 6 4 5 R16 D8 R24 R27 A L3 R28 1 C30 3 WAD CLS 2 R4 R40 J2 1 2 Title D ate: 2 Revision Letter RTN 1 A MAX5969B MAX5974A FL3.3V&5VPD Size 4 VSS 3 S heet of Drawn By: 4 Page 3 of 4 IEEE is a registered service mark of the Institute of Electrical and Electronics Engineers, Inc. Related Parts MAX5969B IEEE 802.3af/at-Compliant, Powered Device Interface Controllers with Integrated Power MOSFET Automatic Updates Would you like to be automatically notified when new application notes are published in your areas of interest? Sign up for EE-Mail™. Application note 4940: www.maxim-ic.com/an4940 More information For technical support: www.maxim-ic.com/support For samples: www.maxim-ic.com/samples Other questions and comments: www.maxim-ic.com/contact AN4940, AN 4940, APP4940, Appnote4940, Appnote 4940 Copyright © by Maxim Integrated Products Additional legal notices: www.maxim-ic.com/legal Page 4 of 4