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TPS23880: Power negotiation with LLDP

Hubertus Klein
Prodigy 60 points
Part Number: TPS23880

Hi,

in one of our devices we use the TPS23880 poe chip and configured it to provide a maximum power of 60W (Class 6 and not higher). The connected PD is a camera that requires a maximum power

of 50W (inclusive IR and motor) and if the IR and motor are not used, the input power is less than 30W. According to the manufacturer the camera does not support power negotiation via LLDP,

so I thougth that the camera should be classifed as a class 6 PD. But it is always classified as a class 4 PD. The problem is that if IR and/or motor are used, the required power is higher

than the initially specified 30W and the TPS23880 stops providing power.

 Is it possible to force the TPS23880 to provide 60W (i.e. to classify the camera as class 6 PD)?

Does the TPS23880 support power negotiation?

 

Many thanks and best regards

Philipp

  • 0
    TI__Genius 12355 points

    Hi Phillip,

    LLDP is not very common in PoE as this is a requirement by the load's software to communicate through the data lines to the PSE. Typically this is more expensive and adds complexitity with no signigifacnt advantage.

    As for the power negotiation and flexibility for this appliation there are a couple different solutions that can work:

    1. TPS23880 enables adjustable Pcut value. You can adjust Pcut values to the specific ports to allow for up to 60W. Therefore the classification will remain the same at 30W (Class 4) and not trigger a fault condition when power need is >30W. This will require you to operate in manual mode as the port policing limits will need to be adjusted as well, since in auto and semi auto mode these bits are set automatically.

    2. Disable Pcut so that the port will not be automatically turned off during a 4P-Pcut fault condition. 

    3. Operate in manual mode and disable classification and detection to manually turn the port on. Using this method you will manaully have to configure your power limiting settings for the ports.

    TPS23880 supports programmable power limiting which is what I mentioned in point #1. Power negotiation is done through the handshake process which is IEEE802.3 spec.

    Very Respectfully,

    Brandon Beader