What is the definition of the MP8004 PG output? Lo = detect, Lo = classify, Lo = PD pass switch turned on, etc.
From the block diagram below, there is a FET label HV. This FET turns off/ on based on the input detection and classification. The FET will also turn off if the current through Rsense is too high. The drain of the HV FET is connected to RTN pin. This FET will conduct when classification and detection are finished. When the FET conducts, RTN voltage falls.
So, PG is low when RTN is falling which means that input is good. Low PG means the input sources and PD are good for power transfer.