LTC4278　how to achieve PoE dominace

Question

Hi, 
 I can find a reference circuit on the datasheet to achieve an Auxiliary dominant configuration like Figure 9, 
 is there a reference for making PoE dominant? Hope you can give me some advice. 
 
 Best Regards, 
 Leo

ADIApproved · Accepted Answer

Hi Leo, 
 Apologies for the late response. What is the voltage range for the auxiliary supply? Do you want PoE Priority even if the auxiliary is connected first? Assuming the auxiliary supply is between 42V to 57V: 
 
 This circuit inserts power before the LTC4278 interface controller. In this configuration, it is necessary for the wall adapter to exceed the LTC4278 UVLO turn-on requirement. This option provides input current limit for the adapter, provides a valid power good signal and simplifies power priority issues. As long as the adapter applies power to the PD before the PSE, it will take priority and the PSE will not power up the PD because the external power source will corrupt the 25k signature. If the PSE is already powering the PD, the adapter power will be in parallel with the PSE. In this case, priority will be given to the higher supply voltage. If the adapter voltage is higher, the PSE should remove the port voltage since no current will be drawn from the PSE. On the other hand, if the adapter voltage is lower, the PSE will continue to supply power to the PD and the adapter will not be used. Proper operation will occur in either scenario.)

Electronic Design Services - PartnerZone

Products Mentioned

LTC4278　how to achieve PoE dominace

Products Mentioned

LTC4278 how to achieve PoE dominace

LTC4278　how to achieve PoE dominace