I use the NCE3401 Pmos tube, I will automatically connect the S and D pins wrong, regardless of this, according to the connection in the figure, D to S is always on, assuming that when VIN input 12V, Vbus does not input voltage, In theory, the PMOS is cut off. There should be a diode reversed from S to D at 12V. The voltage should not pass. Theoretically, VD=Vbus is 0V, but I measured the vbus to be more than 10V. This is what happened.
Benicio Publicado en July 3, 2020
I think it may be possible to analyze this way: DS leakage current also exists in the off state of the Pmos tube, which can be regarded as a large resistance R1 between DS. Vs=12-0.3=11.7V. When you measure the floating Vbus pin, the multimeter also has a large resistance to ground, R2, R1 and R2, and you get a voltage of more than 10V. You can try to add a resistance of tens of K between Vbus and ground. It is estimated that this voltage will drop.
Colbie Publicado en July 3, 2020
The parasitic diode inside the MOS tube has always been in the on state, and the control pin will be turned on regardless of the level. Now this way, it does not play the anti-reverse effect you want.
Bernadette Publicado en July 3, 2020
Judging from your circuit diagram alone, there is no voltage in VBUS. Is it that the MOS is reversed or find it from other places?
