I am designing a high side switch using P-Mosfet to drive a heat element. The Mosfet is driven by PWM from MCU, which in the test is around 40Hz, 10% duty.
I am facing 2 issues here, one is that there is a unexpected amount of voltage drop between Source and Drain of the P mosfet, when the Mosfet is turned on. From the scope shot, we can see the voltage drop is around 3V. Where is the voltage drop coming from? The Rdson of the is pretty small, around 7mOhm or less. The current is maximal 6A, should the voltage drop just be maximal 28mV, right?
The other issue I am facing is that when switching the heating element using PWM, the circuit is runing with audio humming. Is there some way to over coming this? Here is the scope shot with the rising edge.
Any hint is appreciated. Thanks