Tool/software:
Hi TI Team，
Hello, we want to use the 23881 for POE port control. In Germany, they want to achieve the on and off of any POE using physical switches. I saw that the 56th pin OSS can switch on and off the POE control signal. If a physical switch is used, it can be done directly
Is it feasible to directly ground the G-terminal signal of the MOS? Do you have a more rigorous and better control plan?
Hi Ken,
OSS pin is an active high pin with an internal pulldown to GND.
Do you need a mechanical switch or will the behavior be GPIO controlled from MCU in addition? You make use a simple switch controlled MOS logic circuit to control the behavior. I would not recommend using a mechanical switch to directly control the pull-high condition on the OSS pin.
Below schematic is a simple solution I would recommend, your boot capacitor on the gate pin of the PMOS should be ~10x the gate capacitance of the PMOS. I would recommend using a current limiting gate resistor ~10kohm should be sufficient. This control circuit will eliminate ringing caused by the mechanical switch. Recommend going with a very poor performing PMOS which will also help eliminate any ringing from the mechanical switch naturally.
If you have MCU control switch of the OSS pin you can replace the mechnical switch with a NPN BJT as the low side switch and tie the base to your GPIO with a current limiting resistor and your emittor tied to ground and collector tied to the gate of the PMOS.
Regards,
Brandon
