Hello,
I have a question concerning PM8805 and the related evaluation board STEVAL-POE005V1.
From my understanding in the evaluation board the PGD signal is pulled-up by a resistor to VB.
Now, when I power the board only by RAUX, where does the voltage come from? VB will be powered internally in PM8805 by VDD. But VDD comes from before the hot swap MOSFET. RAUX is inserted behind that hot swap MOSFET and the MOSFET is disabled. So, what I see, VDD is not powered i.e. disconnected from RAUX. Besides, in PM8805 datasheet example, PGD is pulled high by VDC i.e. VOUT. This configuration I clearly understand as VDC is powered directly by RAUX. So where does the VB voltage come from in RAUX-only operation? Could you please clarify that? What does the circuit work (and it does as we can see in STEVAL-POE005V1).
Thanks for an answer in advance.
Best regards, Alex
