This is a circuit to control the power supply on and off.AO3401 is an enhancement PMOS, simply put, when Vgs (i.e., the voltage between 1-2 of Q7) has a negative voltage, Q7 will conduct, for the AO3401, the full turn-on voltage is about -10V, but -3.3V can also be basically conductive, just a little bit higher impedance (about 100 milliohms), specific different Vgs The specific on-state impedance at different Vgs can be found in the AO3401 manual. For the circuit in the figure, when CMMB_PWRON is greater than or equal to 3.3V, the AO3401 is in the off state, and no power is supplied to the back-end circuits, and when CMMB_PWRON is 0V, the AO3401 conducts, and the back-end circuits are supplied with power. When using this switch, L12 should not be soldered, otherwise this circuit is meaningless.The AO3401 manual can be found at www.alldatasheet.com网站查询下载