5.2 Bootstrap Operation

The supply for the MCP14LH2106(4) High-Side is provided by the bootstrap capacitor C_B (see Figure 5-2). In the half-bridge configuration, V_S swings from 0V to V_HV depending on the PWM input of the IC. When V_S is 0V, V_BS will go below V_CC, and V_CC will charge C_B . When HO goes high, V_S swings to V_HV, and V_BS remains at V_CC minus a diode drop (D_B), due to the voltage on C_B . This is the supply for the high side gate driver and allows the gate driver to function with the floating well (V_S ) at the high voltage.

When considering the value of the bootstrap capacitor C_B , it is important to size it so that it provides enough energy to quickly drive the gate of Q_H . Values of 1 μF to 10 μF are recommended. The exact value depends on gate capacitance and the noise level appropriate for the application. It is key to use a low ESR capacitor that is close to the device. This will quickly supply charge to the gate of the MOSFET.