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LM5072 support 802.3at

Ben Chen75
Prodigy 250 points

We have used LM5072 as an IEEE802.3at PD module based on reference design of NI's LM5072-5V/25W (snvu110). Recently, our customer found that some POE+ switches are unable to deliver power more than 15.4W. We did not implement two-event detection circuitry (sheet 3). Thus, our customer think that is the root cause for type-2 classification failure. As we study the design of 2-event detection circuitry depicted in document snvu110, it seems that the 2-event detection result is connected to a LED only but not taken effect on LM5072. Can you confirm that 2-event detection do not take effect on LM5072 during type-2 classification? Thanks!

  • 0
    TI__Mastermind 42795 points

    Ben,

    The type 2 detection ability of the PD is to be used by the PD load (micro-processor, etc.) to manage power consumption based on detected PSE type (1 or 2). So, the 2-event result LED is for EVM display only. Normally, this LED will be paired with photo transistor to notify the secondary side load of which PSE type is connected.

    Any type 2 PD must also have software (micro-processor side) that can communicate back to the PSE side processor via LLDP. THis is for the case where the PSE is type 2 but does not furnish 2-event class but uses LLDP based class instead.