National Semiconductor LM5072 Manual Download

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

National Semiconductor
LM5072
Honsun Tan
February 2008

1.0 Design Specifications

Inputs

Output #1

VinMin=38V

Vout1=12V

VinMax=60V

Iout1=2.1A

2.0 Design Description

This LM5072 25W PoE PD Power Eval-board is specially de-
signed 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 fig-
ure 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 de-
tection 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 con-
necting 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 sig-
nificantly 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 se-
lection 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-domi-
nance 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 de-
tailed test results.

3.0 Features

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.
Versatile Input Power Options
 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.
Full Protection for PoE
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
Uses Standard Transformer FA2900 from Coilcraft
This Eval-board is easily modified to 3.3Vdc, 5Vdc, 9Vdc and
15Vdc output with standard Coilcraft transformers FA2677,
FA2898, FA2899 and FA2901 respectively.