I've got a strange problem with a MOSFET (IRLML2502PBF). I've used it in several places within my circuit with no problems but I am having an issue with one particular implementation. It's a logic level N Channel FET with a very low Vgs threshold (.65V). The FET is not sinking a large current (on the order of 20mA) and the load is not inductive. I've switched much larger loads with this particular FET. I have driven these particular FETs directly from a microcontroller in the past.
The problem is that the FET fails to turn on when driven by a single gate inverter (NC7S04). It's very difficult to troubleshoot because the problem goes away as soon as I attach a scope probe to it. My first thought was a bad solder joint. I found this was not the case. So, I tried adding a large impedance between the gate and ground (10k). This does the trick. It happily works that way... but I would really like to know why!
The connection between the inverter and the gate is direct (no series resistance) and there is no pullup.
Any suggestions?
The problem is that the FET fails to turn on when driven by a single gate inverter (NC7S04). It's very difficult to troubleshoot because the problem goes away as soon as I attach a scope probe to it. My first thought was a bad solder joint. I found this was not the case. So, I tried adding a large impedance between the gate and ground (10k). This does the trick. It happily works that way... but I would really like to know why!
The connection between the inverter and the gate is direct (no series resistance) and there is no pullup.
Any suggestions?