Hello NXP team,
I hope this email find you well,
I want to ask about the MOSFET connected to the Brake Resistor Terminal in the inverter board Devkit MotorGD as shown below. I find that, in its data sheet, its gate needs 10 V to drive the MOSFET, so how to provide such voltage from the microcontroller board MPC5744P to drive this MOSFET to operate the brake resistor.
When I tried to drive it using 5V, its voltage dropped when connecting a brake resistor and it can't switch on and off.
Hello Peter,
-By "its voltage," I mean the MOSFET's gate voltage. The voltage on the pin G7 from the MCU board, which will be connected to the gate of the MOSFET on the inverter board, is nearly 5V, but when attaching the MCU board (MPC5744P) to the inverter board (DevkitMotorGD), even before connecting a brake resistor, the voltage of the pin G7 drops to half the value (around 2.5V), and then when connecting the brake resistor, this voltage can't drive the gate off the MOSFET, I think.
-Regarding the value of brake resistance that I used, I used several resistances as shown below
- BTW, I intend to use the brake resistor as a dump load for the machine that will work as a generator
Best Regards,
Ahmed
Hello,
There is level shifter - by deafult set to 3.3V. Could you check if you have it at 5V?
The selection of the brake resistor also depends on the power rating of the resistor. The smaller the resistance, the higher the power rating needs to be. It shouldn’t be too small because a large current can flow very quickly and destroy it. You also need to check and consider the power rating and maximum current of the MOSFET, because the current will flow through it as well, and it’s relatively weak in a small package (SOT-23). There are a few amps there… According to the SOA, you can go somewhere in the range of ±5 A, but I’m not sure if such a small package can dissipate heat fast enough for that current.
If you want to use some other load instead of a brake resistor, it’s the same story.
Best regards,
Peter