lm5072mhx-80 National Semiconductor Corporation, lm5072mhx-80 Datasheet - Page 16

• Manufacturer Part Number: lm5072mhx-80
• Description: Integrated 100v Power Over Ethernet Pd Interface And Pwm Controller With Aux Support
• Manufacturer: National Semiconductor Corporation

www.national.com
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,
FIGURE 10. The FAUX Configuration
FIGURE 11. The RAUX Configuration
16
when the auxiliary supply voltage is much lower than the PoE
input voltage, the RAUX option is more favorable because 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 protected. If complete
reverse protection is desired, series blocking diodes are nec-
essary.
20184628
20184627