Power MOSFET switch over heating. Melting solder,

[guscrown]

Alright, continuing with the debugging of my new board tonight I found another issue worse than the one before: My switching MOSFET is getting so hot that I'm getting molten solder.

I replaced the MOSFET with a short circuit just to see if the components sorounding the MOS were the cause of the problem (mostly a big Inductor I have right next to it) but the copper reaches a temperature of 110F, not enough to melt solder.

This is my schematic:

As you can see, my Vgs is around -11V and I'm running 3A through it using an Electronic Load. Based on the datasheet here: http://www.onsemi.com/pub_link/Collateral/NTD20P06L-D.PDF this thing can do up to 15.5A.

Any ideas of what might be going on?

The only thing I could think of was that the heat on the copper could be increasing Rds(on) but at that particular low current it shouldn't be so serious.

I am using the TO-252-3, DPak (2 Leads + Tab) package.

[Rerouter]

if you dont switch your mosfet very fast you it acts like a big resistor, that 100K is far too weak a pull up, configure a pnp-npn push-pull amplifier on the output of your op amp instead, you really need it moving quickly, to prevent all that heat as it slowly turns off,

[guscrown]

I am not switching it. It is being used in steady state.

[amyk]

Then it's not switched on fully and still acting as a resistor. Measure the voltage drop across it.

[SeanB]

You need to be using a P type mosfet there as a high side switch. You will have a high voltage drop across it in this application, probably 6V or more