Barry Signoretti Joe DeNicholas 10/20/04

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1 Power Supply Design for Power over Ethernet Powered Devices Barry Signoretti Joe DeNicholas 10/20/04 1

2 Agenda Introduction PoE Architecture Power Sourcing Equipment & Powered Device LM5070 Conclusion 2

3 The Killer App. Voice over Internet Protocol (VoIP) is the application that is driving the need for Power over Ethernet (PoE). LAN telephony lowers the cost of capital, installation, support and operation of voice communications. However, voice services are critical during emergencies when power is lost. PoE satisfies the lifeline function. 3

4 PoE Can Support Other Applications In applications such as wireless access ports, security cameras, badge readers, RFID readers, cordless phones, etc. AC power must be routed to remote locations at a cost that can easily exceed the cost of the equipment and the routing of an Ethernet cable. The appliance can be easily moved, to wherever you can lay a LAN cable, no hazardous voltages anywhere. A UPS can guarantee power to the appliance during mains power failure. Appliances can be shut down or reset remotely. Simplifies the installation of wireless LAN systems. 4

5 Power Over Ethernet Cables? Challenges Utilize the existing physical medium. No degradation in data flow performance. Operate in a legacy environment. Not pose a safety hazard. Low cost. Hot Plugging. 5

6 PoE Solution, IEEE 802.3af Source power from the same location as the Ethernet switch/hub. Distribute un-interruptible telephony level power (48VDC). Use existing cat5 / cat6 cabling used for 10baseT, 100baseT and 1GbaseT. Prevent damage to any non-poe devices that may be attached to the power sourcing equipment. Accommodate any pre-standard implementations when possible. Source sufficient power to address future applications. i.e. video phone. 6

7 Power Over Ethernet Architecture 7

8 PoE System Enet Switch µp Ethernet Phy Ethernet Phy PD µc PSE Control - + PSE 48V PS LM5070 LM5070 8

9 Media Dependant Interface (MDI) Alternative B: Power can be sourced from the PSE through spare lines in the CAT-5 cable. Alternative A: Power can be sourced from the PSE through the data lines via data transformer center taps. 9

10 Power over Ethernet Power Sourcing Equipment (PSE) And Powered Device (PD) 10

11 Power Sourcing Equipment (PSE) Functions Detect the attachment of a PD to the link. Classify the PDs power requirements (optional). Supply power to the link section only if a PD is detected. Monitor the power on the link. Scale power back to the detect level when power is no longer requested or required. 11

12 PD detection PSE shall not apply operating power to the PI until the PSE has successfully detected a PD. The PSE is not required to continuously probe to detect a PD signature. A PSE may successfully detect a PD, but may then opt not to power the detected PD. A PSE shall accept as a valid signature a link section with Signature resistor = 23.75KΩ KΩ and Parallel signature capacitor = 0.05µF µF 12

13 PD Signature Voltage Offset (V) PD Signiture Detect.ckt-Transient-3 Time (s) u u u u R = V I Slope = ( V 2 V 1) /( I 2 I 1) V Source V PD V Source = 2.8V TIME u V(3) V(IVM1) D(TIME) 0.0 D(V(IVM1)) 0.0 PSE forces two voltages between 2.8V & 10V. 13

14 PD Signature Capacitance (V) PD Signiture Detect 2.ckt-Transient-18 Time (s) m m m m m m m m C = t I V V R TIME m V(5) D(TIME) 0.0 D(V(5))

15 PD Classification IEEE802.3af allows for the classification of PDs based upon their power requirements to permit load management. Force a voltage between 15.5V & 20.5V for a max. of 75mS and measure current. Measured I Classification Max PD Power 0mA to 5mA 8mA to 13mA 16mA to 21mA 25mA to 34mA 35mA to 45mA Class W Class 1 Class 2 Class 3 Class W 6.49W 12.95W Reserved 15

16 Discovery, Classification and Application of Nominal Voltage Voltage 42V Discovery: 25K Ohm Impedance Classification: Constant Current, 4 Ranges, Max 30mA 30V Classification 15.5V 10V 2.8V Discovery 500mS Turn On 400mS Classification 75mS Operational Phase 16 Time

17 Maintain Power Signature (MPS) PSE must remove power if MPS is invalid. AC Component, (500Hz Max. Vac_pp < 10% Vport) Valid: Z 27KΩ Invalid: Z 1.98MΩ DC Component Valid: I 10mA for 60mS Invalid: I 5mA for 400mS PSE may monitor EITHER or both components 17

18 PD Power Supply Input at PI Input Voltage V port = 36-57VDC Average Power P port = 12.95W max. Input Current I port = 350mA 37VDC I port = 230mA 57VDC Inrush Current at Startup I inrush < 400mA Operating Input Capacitance C port = 5µF min. Backfeed Voltage (Voltage coupled to non-power pair) B vfb = 2.8V max. 18

19 The LM5070 PoE Powered Device Interface & PWM Controller 19

20 RJ45 Connector LM5070 Powered Device (PD) System Partitioning The LM5070 Integrates: Signature Detection + Classification + UVLO / OVLO + Hot-plug controller + PWM Controller VDC TX+ (1) TX- (2) RX+ (3) RX- (6) (4) (5) To PHY To PHY IEEE 802.3af Interface UVLO Signature Detection Classification Hot Plug Controller In-rush and Fault Current Limiting LM5070 DC-DC Converter Controller Current Mode (7) (8) 20

21 LM5070 PD Interface and PWM Controller PD Interface Features: Fully Compliant to 802.3af 75V, 1W, 400mA MOSFET Program Inrush Current Limit Current Limit Protection Program Classification Current Under-voltage Lockout Thermal Overload Protection Signature Resistor Disconnect Package: TSSOP-16, LLP-16 VIN UVLO UVLORTN RCLASS RSIG RCLP VEE VIN 10uA 60V VCC > 5V + EN 1.5V _ + _ + _ 2V 2V 10V VIN 1.5V _ + _ + LT20V LOCKOUT _ + Thermal Limit Gate Control 1.5V VBG + Power OK - LOCAL_EN + _ EN Switch Mode Power Supply Controller VCC OUT SS RT CS COMP FB ARTN RTN 21

22 LM5070 Current Mode Controller Borrowed from Popular LM5020 PWM Controller Features: Internal HV Start-up Bias Regulator Current Mode Control Internal Reference Error Amplifier Internal Slope Compensation (-80) Cycle-by-Cycle Over-Current Protection 1.25V 800 ma Peak Gate Driver Max Duty Cycle Limiter, FB 80% (-80) or 50% (-50) SS Leading Edge Blanking Programmable Soft-Start COMP Programmable Oscillator with Sync Direct Optocoupler Interface Thermal Shutdown (165 C) -50 Device Has No Slope Compensation 5V 5K 1.4V 2K 100K 50K 0.5V 45uA 0 PWM Slope Compensation Generator 80% MAX DUTY LIMIT (-80) 50% MAX DUTY LIMIT (-50) CURRENT LIMIT LOGIC CLK OSC S R SET CLR Q Q 10uA CLK +LEB VCC DRIVER SS RT OUT SS CS 22

23 Programmable UVLO Threshold and Hysteresis Example Calculation: 40V UVLO Release with 6V of Hysteresis (34V UVLO) R2 (1) 40V = 2.0 R1 + R2 GND R1 10uA LM5070 (2) (3) (4) 6V V 10µ A R1 R2 R1 + R 2 = 0.300V = R 1 R = 30kΩ 2 = 30kΩ Hysteresis Voltage at UVLO Pin UVLO Hysteresis Current -48V Using (1) and (4), we can calculate R1 = 600kΩ and R2 = 31.6kΩ. R2 UVLO (4) UVLORTN (5) VEE (7) 2V _ + Voltage Drop Negligible 23

24 Startup Operation RTN VCC Default Inrush Current Inrush Current Limit Programmed to 150mA Inrush Reverts Back to 350mA When PowerOK = 1 VCC Released When PowerOK = 1 Softstart Released When VCC Achieves Regulation *PowerOK is an internal signal. Inrush Current VCC RTN 24

25 Thermal Event Testing TLIM Sensor ILIM Sense FET Startup Conditions: Input voltage: 50V Load Capacitance: 100uF Sequence Length: ~14ms. Average Power Dissipation: 9.4W Energy Dissipation: 135mJ Peak FET Temperature: 140 C (ceramic pkg.) Images shot with high speed IR camera from Oak Ridge National Labs in Tennessee. 25

Fault Operation RTN pin 200mA / div Thermal limit adds one final layer of protection against faults and other events that may exceed safe operating area.

26 Fault Operation RTN pin 200mA / div Thermal limit adds one final layer of protection against faults and other events that may exceed safe operating area. +10V Softstart Pin 2V / div RTN Pin 1V / div VIN VIN LM5070 VCC +3.3V Programmable controller over-current protection limits initial current spikes, set very high (>3A) RSIG VEE UVLO UVLORTN RCLASS RCLP VEE RT SS COMP OUT CS RTN ARTN FB LM V DC current increases beyond 375mA in the main power MOSFET. Current limit amplifier puts the FET in saturation, causing the drain (RTN) to rise. When RTN increases above 2.5V wrt VEE, PowerOK = 0, softstart is discharged, and the part continuously attempts to restart. 26

27 LM5070 High Efficiency Demo Board Performance: IEEE 802.3af Compliant Input Range: -38 to -60V Output Voltage: 3.3V Output Current: 0 to 3.4A Board Size: 1.75 x 1.25 x 0.6 Operating Frequency 250KHz Programmed UVLO Release at 41V Current Limit Protection Isolated Output Ground Measured Efficiency: 90% Peak 27

28 LM5070 High Efficiency Demo Board 28

29 LM5070 Economic Demo Board 29

30 Conclusions PoE is market with CAGR = 64%. The VoIP phone is the application that is driving PoE but numerous applications are emerging. The LM5070 is the Best In Class solution for the PD power supply and other high voltage power supply applications requiring hot-swapping. 30

31 Thank You! If you have questions for our presenter, please send them to our customer response center at The online technical journal National Edge is available at Sign up for National s monthly newsletter, News@National by updating your online profile at 31

32 Power Supply Design for Power over Ethernet Powered Devices Barry Signoretti Joe DeNicholas 10/27/04 32

33 LM5070 High Efficiency Demo Board Performance: IEEE 802.3af Compliant Input Range: -38 to -60V Output Voltage: 3.3V Output Current: 0 to 3.4A Board Size: 1.75 x 1.25 x 0.6 Operating Frequency 250KHz Programmed UVLO Release at 41V Current Limit Protection Isolated Output Ground Measured Efficiency: 90% Peak 33

Obsolete. Power-over-Ethernet Interface PD Controller Meets IEEE802.3af TM Standard PHY

Obsolete. Power-over-Ethernet Interface PD Controller Meets IEEE802.3af TM Standard PHY Features Power-over-Ethernet Interface PD Controller Meets IEEE802.3af TM Standard Implements IEEE802.3af standard for PD 400mA inrush current limit 350mA operating current 400mA fault current limit Fast