13.21.1.3 Bootstrap Mode

The high-side driver obtains the high-side biasing voltage from the V_BOOT LDO, bootstrap diode and bootstrap capacitor. The bootstrap capacitors must first be charged before the high-side drives may be used. The bootstrap capacitors are all charged by activating all three low-side drivers. The active low-side drivers pull their respective phase nodes low, charging the bootstrap capacitors to the V_BOOT LDO voltage. The three low-side drivers should be active for at least 1.2 ms per 1 µF of bootstrap capacitance. This assumes a 12V voltage change and 30 mA (10 mA per phase) of current coming from the V_BOOT LDO.