7.3.3 VCPH Charge Pump: High-Side Gate Supply

The DRV8305-Q1 uses a charge pump to generate the proper gate-to-source voltage bias for the high-side N-channel MOSFETs. Similar to the often used bootstrap architecture, the charge pump generates a floating supply voltage used to enable the MOSFET. When enabled, the gate of the external MOSFET is connected to VCPH through the internal gate drivers. The charge pump of the DRV8305-Q1 regulates the VCPH supply to PVDD + 10-V in order to support both standard and logic level MOSFETs. As opposed to a bootstrap architecture, the charge pump supports 0 to 100% duty cycle operation by eliminating the need to refresh the bootstrap capacitor. The charge pump also removes the need for bootstrap capacitors to be connected to the switch-node of the half-bridge.

In order to support automotive cold crank transients on the battery which require the system to be operational to as low as 4.4 V, a regulated triple charge pump scheme is used to create sufficient V_GS to drive standard and logic level MOSFETs during the low voltage transient. Between 4.4 to 18 V the charge pump regulates the voltage in a tripler mode. Beyond 18 V and until the max operating voltage, it switches over to a doubler mode in order to improve efficiency. The charge pump is disabled until EN_GATE is set high to reduce unneeded power consumption by the IC. After EN_GATE is set high, the device will go through a power up sequence to enable the gate drivers and gate drive supplies. 1 ms should be allocated after EN_GATE is set high to allow the charge pump to reach its regulation voltage.

The charge pump is continuously monitored for undervoltage and overvoltage conditions to prevent underdriven or overdriven MOSFET scenarios. If an undervoltage or overvoltage condition is detected the appropriate actions is taken and reported through the SPI registers.