Hi,
we need to use the 48 to 57V PoE rail voltage after classification for a local load, which does not need galvanic isolation. See our schematic attached.
We have designed a low-side switch, which disconnects the load at power-up, in order not to interfere with classification. After the classification is done and PoE voltage rises to nominal values, the 39V Zener D17 breaks through and puts a positive bias on the gate, effectively connecting the load.
When we do it with a commercially available PoE converter, this works fine. However, our tps23754 schematic will not work: LED3 will not come on, the PoE voltage stays at around 36 V and the tps23754 gets really hot. I suspect that the hotswap FET is not fully engaged for some reason.
Do you see anything wrong in our design?
The 12v output of the flyback only supplies app. 2-3W of power.
BR
Michael