8.3.1.4.2 TDRIVE: MOSFET Gate Drive Control

The TDRIVE component is an integrated gate drive state machine that provides automatic dead time insertion through handshaking between the high-side and low-side gate drivers, parasitic dV/dt gate turnon prevention, and MOSFET gate fault detection.

The first component of the TDRIVE state machine is automatic dead time insertion. Dead time is period of time between the switching of the external high-side and low-side MOSFETs to make sure that they do not cross conduct and cause shoot-through. The DRV8343-Q1 device uses V_GS voltage monitors to measure the MOSFET gate-to-source voltage and determine the correct time to switch instead of relying on a fixed time value. This feature lets the dead time of the gate driver adjust for variation in the system such as temperature drift and variation in the MOSFET parameters. An additional digital dead time (t_DEAD) can be inserted and is adjustable through the registers on SPI devices.

The second component of the TDRIVE state machine is parasitic dV/dt gate turnon prevention. To implement this component, the TDRIVE state machine enables a strong pulldown current (I_STRONG) on the opposite MOSFET gate whenever a MOSFET is switching. The strong pulldown occurs for the TDRIVE duration. This feature helps remove parasitic charge that couples into the MOSFET gate when the voltage half-bridge switch node slews rapidly.

The third component implements a gate-fault detection scheme to detect pin-to-pin solder defects, a MOSFET gate failure, or a MOSFET gate stuck-high or stuck-low voltage condition. This implementation is done with a pair of V_GS gate-to-source voltage monitors for each half-bridge gate driver. When the gate driver receives a command to change the state of the half-bridge it starts to monitor the gate voltage of the external MOSFET. If, at the end of the t_DRIVE period, the V_GS voltage has not increased the correct threshold, the gate driver reports a fault. To make sure that a false gate drive fault (GDF) is not detected, a t_DRIVE time should be selected that is longer than the time required to charge or discharge the MOSFET gate. The t_DRIVE time does not increase the PWM time and will terminate if another PWM command is received while active. In the SPI device, for IDRIVE bit settings of 0000b, 0001b, 0010b, and 0011b, a longer t_DRIVE time of 20-µs is automatically selected by the TDRIVE_MAX bit. If the 20-µs t_DRVIE time is not required, write a 0 to the TDRIVE_MAX bit to disable it and set the t_DRIVE time by the TDRIVE bits. For all other IDRIVE settings, writing to the TDRIVE_MAX bit is disabled. This option is not available in the H/W device.

For additional details on the TDRIVE settings, see the Register Maps section for SPI devices and the Pin Diagrams section for hardware interface devices. Figure 21 shows an example of the TDRIVE state machine in operation.

Figure 21. TDRIVE State Machine