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TPS2378: UVLO is higher than minimum PD input voltage

Chaojin He
Prodigy 30 points
Part Number: TPS2378
Other Parts Discussed in Thread: TPS2375, TPS2377, TPS2376

The operating voltage for type 1 PD is 37V ~ 57V, but TPS2378 has a rising UVLO at 38.1V. Also the electrical specs from datasheet is under VDD 40V~57V. So does this chip meet IEEE 802.3at requirement? Or how should I interpret this spec?

  • 0
    TI__Genius 9230 points

    Hi Chaojin,

    The TPS2378 is a type 2 PD, so the standard spec is 42.5V-57V. That is why the minimum Vdd is 40V. As for the rising UVLO, the PSE should be able to easily clear that during startup. See table 2 on page 14 of the datasheet. The minimum static output voltage of the PSE (for type 2) is 50V. The 42.5V spec at the PD input is there to take into account the losses incurred across the Ethernet cable.

    Thanks,
    Tom

  • 0 in reply to Thomas Amlee
    Prodigy 30 points

    Really appreciate your help. I need to implement type 1 class 3 PD, do you mean it won't be compliant if use TPS2378? Table 1 shows the resistor setting for each class.

    What PD interface IC do you recommend?

  • 0 in reply to Chaojin He
    TI__Genius 9230 points
    Hi Chaojin,

    The falling UVLO of 32V allows for enough margin for operation at 37V (as long as the rising UVLO is met during startup).

    If you would like a PD for type 1 operation, I would recommend these:
    TPS2375 - 802.3af compliant UVLO limits
    TPS2377 - legacy UVLO limits
    TPS2376 - programmable UVLO

    See page 4 for the above UVLO values: www.ti.com/.../tps2376.pdf

    - Tom