RD-163 - LM5072 12Vout 25W PoE PD Power Eval-Board for IP Camera

This LM5072 25W PoE PD Power Eval-board is specially designed for IP Net Cameras powered by PoE. As the PD side’s power converter of a PoE system, this Eval-board converts 48Vdc to 12Vdc to directly power the motor driver for the IP Net Camera’s body rotation and zoom lens. Other regulators such as LM26400 from National Semiconductor can be used to convert the 12Vdc to 3.3Vdc, 2.5Vdc, 1.8Vdc and 1.2Vdc to power the processor of an IP Net Camera as shown in figure 11. This board can provide total power up to 25W as specified by the PoE Plus IEEE802.3at standard. In addition, this Eval-board can be interfaced to any PSE that follows detection and classification procedures defined by the IEEE802.3af standard. In summary, this Eval-board is the ideal solution for a Pre-PoE Plus IP Net Camera application.

This design has 2 auxilliary inputs to allow use of inexpensive 12Vdc and 24Vac regulated adapters to take advantage of the LM5072’s versatile auxiliary power options. 12Vdc power can by provided to the load, bypassing the LM5072, by connecting a 12Vdc regulated adapter to the 12V AUX Input Port.

When regulated 12Vdc is available, it can be delivered directly to the load, bypassing the LM5072, by connecting to the 12V AUX Input Port. When the regulated 12Vdc is present at the 12V AUX input port before 48V PoE voltage is present, the PoE startup signature detection resistance of the PD is significantly reduced. This signals the PSE to not deliver power to the PD. If 12Vdc is added after 48V PoE voltage is present, the PD signature resistance changes and will signal the PSE to stop providing power to the PD. In either case the regulated 12Vdc will turn off the LM5072 and can reduce power losses from the converter and the PoE line.

The LM5072’s RAUX configuration is utilized for the 24V AUX input port to bypass the internal hot swap MOSFET allowing the 800mA current limit of the LM5072 to be ignored. This allows the input voltage for the 24V AUX input port to go down to 16Vdc and up to 60Vdc. A key function for automatic selection of supply Dominance Option is implemented for the 24V AUX input port. By connecting pin 1 and pin 2 by a jumper, as shown in figure 4, the 24V AUX is made to be the dominant input voltage, even if 48V PoE input voltage is present. Alternatively, if pin 2 and pin 3 are jumpered, as shown in figure 4, the LM5072 will be placed in non-dominance mode.

The theory and general application of PoE is beyond the scope of this document. For detailed PoE information, please see the LM5072 datasheet.

This document includes a schematic, BOM, layout and detailed test results.

•	RD-163 Reference Design Document

Additional Product Resources

Board Photo

Energy Efficient Eval-Board

• DC/DC converter efficiency of 89% at PoE 48Vin with 25W Load.
• Overall efficiency of 85.5% at PoE 48Vin with 25W load.
• DC/DC converter efficiency of 90% at 24Vin with 25W load.
• Overall efficiency of 89% at 24Vin with 25W load.

• PoE input Port: 38Vdc-60Vdc range with PoE interface.
• 24V AUX input Port: 24Vac from inexpensive 24Vac adapter or 16Vdc-60Vdc range
• 12V AUX input Port: Regulated 12Vdc from inexpensive 12Vdc adapter.

• Compliant 802.3af PD interface
• Inrush current limit.
• Accurate 800mA over current protection.
• Short-circuit protection, hiccup mode.
• Input UVLP with 7V hysteresis, 37V on and 30V shutdown
• LED indicates power from PoE