MOSFET won’t turn-off at low drain current

Question

I am trying to design a MOSFET driver circuit for a bi-directional DC/DC converter. The load current is about 17A rms Max. Max input voltage will be about 54V DC. The image below is not the whole circuit obviously, just the driver for highside PMOS.

I am not using a bootstrap circuit and NMOS/driver because in some situations I would like the MOSFET to be permanently on.

Now it is not really a problem but when my load current falls below about 2A, the load voltage wont go all the way down to 0V anymore. My guese is due to drain-source capacitance, but I really have no idea. Anyone that can explain this phenomenon to me?

Here is my circuit:

This is the output current and voltage for a large load (R8=5.86 Ohm):

Input signal (V4) and MOSFET output voltage for a large load (R8=5.86 Ohm):

This is the MOSFET switching voltage and current for R8=5.86 Ohm:

Vgs for R8=5.86 Ohm:

This is the output current and voltage for a small load (R8=1k Ohm):

The MOSFET switching voltage and current for R8=1k Ohm.

Vgs for R8=1k Ohm:

I uploaded the LTspice circuit here.

Answer 1

You're simply seeing the RC time constant of various direct and effective capacitances discharged slowly through a quite high load resistance. Your test repeats before this discharge can even complete.