I've been given this schematic to review it (I'm working on a formula student team.) It is used for cutting off the power to a motor through a N-mosfet (NCV8402A). The 12V are being supplied through a battery. The motor will be connected to the connector on the right.
I had a disagreement with the team member that made the board about the use of the R6 resistor. He told me that he used that resistor as a "pull up" to avoid the situation of the pin number 2 floating when the transistor switch opens. I told him that I don't agree because you can't define a pull up resistor without having a ground at your circuit and that the main reason for using a low side switch is for the ground pin to actually "float" because it is an open circuit. I also told him that in normal operation 1.2mA of current will flow through the R6 for no reason.
Who is right?
Best Answer
You're both forgetting that there's a very low resistance path through the motor. If the MOSFET is switched off pin 2 (and the tab) will be pulled high by the motor.
Figure 1. The 10k resistor will have negligible affect compared to the low resistance of the motor.
R6 is not required.