LM5072 datasheet(16/24 Pages) NSC

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Auxiliary Power Options

The LM5072 based PD can receive power from auxiliary

sources like AC adapters and solar cells in addition to the

PoE enabled network. This is a desirable feature when the

total system power requirements exceed the PSE’s load

capacity. Furthermore, with the auxiliary power option the PD

can be used in a standard Ethernet (non-PoE) system.

For maximum versatility, the LM5072 accepts two different

auxiliary power configurations. The first one, shown in Figure

10, is the front auxiliary (FAUX) configuration in which the

auxiliary source is “diode OR’d” with the PoE potential re-

ceived from the Ethernet connector. The second configura-

tion, shown in Figure 11, is the rear auxiliary (RAUX) option

in which the auxiliary power bypasses the PoE interface and

is connected directly to the input of the DC-DC converter

through a diode. The FAUX option is desirable if the auxiliary

power voltage is similar to the PoE input voltage. However,

when the auxiliary supply voltage is much lower than the

PoE input voltage, the RAUX option is more favorable be-

cause the current from the auxiliary supply is not limited by

the hot swap MOSFET DC current limit. A comparison of the

FAUX and RAUX options is presented in Table 3. Note the

ICL_FAUX and RAUX pins are not reverse voltage pro-

tected. If complete reverse protection is desired, series

blocking diodes are necessary.

20184627

FIGURE 10. The FAUX Configuration

20184628

FIGURE 11. The RAUX Configuration

LM5072 Datasheet(PDF) 16 Page - National Semiconductor (TI)