When no external signal pin is desired, charger behavior might be used to provide the control for a bootswitch. This is shown in Figure 4. When the charger voltage exceeds the battery voltage by more than theVgsth of Q2, Q2 comes on drawing current through R3 and R4 and turns on Q1. Q1 provides currentthrough R2 and R1 to provide the boot voltage to TS1. D1 prevents over voltage at the TS1 pin. D3 keepsthe Q1 gate voltage safe when needed. D2 protects the Q2 gate when needed