Hi Michael,
You are correct; the thermal pad will not be grounded with insulating thermal compound.
The thermal slug does not need external grounding, but we consider it good practice to connect the heatsink to ground. In some cases, the screw that holds the heatsink can make the connection.
In addition to the reduction of ground noise, another benefit is protecting the device from accidental voltages applied to the heatsink. Inside the chip, the thermal slug is conductively attached to the substrate of the die. The DRV8332 could be damaged if a voltage is applied to the heatsink and the thermal compound does not completely insulate the heatsink from the thermal slug.
You are correct; the thermal pad will not be grounded with insulating thermal compound.
The thermal slug does not need external grounding, but we consider it good practice to connect the heatsink to ground. In some cases, the screw that holds the heatsink can make the connection.
In addition to the reduction of ground noise, another benefit is protecting the device from accidental voltages applied to the heatsink. Inside the chip, the thermal slug is conductively attached to the substrate of the die. The DRV8332 could be damaged if a voltage is applied to the heatsink and the thermal compound does not completely insulate the heatsink from the thermal slug.