LTC4269-1 for LLDP protocol

Hi,

PD controllers such as the LTC4269-1, exist on the physical layer. The ethernet transformer effectively splits the DC voltage used for PoE from the differential data. The DC voltage goes to the PD controller and the differential data goes to the PHY. The LTC4269-1 does not directly interface with the data layer, so a PHY is required for Link Layer Discovery Protocol (LLDP) negotiations.

Best Regards,

Eric

Hi Eric,

The PSE devices may support HW negotiation

and/or SW negotiation (LLDP/CDP). The PD is required to support both.

Simple POE+ switches usually only perform the HW negotiation and fix the

power provisioning at 30W.

More complex switches, like Cisco 9800 and HP Aruba, show the very

unfortunate phenomenon they negotiate enough power at switch-on of the display.

(The displays remain around 15.5W). As soon as the LED’s switch on and the display

start to run the applications in more power demanding modus, the power request is

of course increasing. Due to the missing LLDP protocol, the display is asking for more

current than is negotiated and that results in an error message on the switch and

(in most cases) rebooting displays. Some switches remain functional: they simply

give an error message, but keep on delivering current, but the more advanced

switches just close the power provisioning.  

(Qus) In other word, due to that LTC4269-1 exist on the physical layer,

hence, it can only communicate with POE+ switches by HW negotiation?

Our customer challenge us that The IEEE 802.3at standard demands the PD

to support LLPD (/CDP), but following Analog’s explanation as above,

LTC4269-1 only exist on the physical layer, hence, it won’t receive/recognize/

even drop the datalink layer/power provisioning packet sent from POE+ switches ?

Or this datalink layer/power provisioning should be handled

by Android OS instead (If the powered device happens to be an Android tablet) ?