I want to measure the Rds-ON of a P-Channel MOSFET and I have setup the test circuit as follows:
I keep the source at constant +10V and vary the step the gate voltage up in the increments of 1V. Then I measure the resistance across the drain & source. However, the RDS values I measure are around 5-5.6 ohms vs the 0.3 ohms as per datasheet. I am using 4 wire measurement and for N-Channel MOSFETs this setup seems to work. So I wonder why it apparently doesn't work for P-Channel MOSFETs.
I tried with other P-Channel MOSFETs and also get considerably high values. So it's not just one MOSFET. For a rough comparison, I tested it on a component tester and even that gives lower RDS ~ 1-1.5 ohms. I understand that I can't trust the component tester results too much but it should be ok for indicative results.
What could be going wrong with the measurements? and is there a better way to measure RDS that would give me accurate results?