For normal operation, inductance in motor (assume larger than 10 µH) is sufficient to provide low di/dt output (for example, for EMI) and proper protection during overload condition (CBC current limiting feature). So no additional output inductors are needed during normal operation.

However during a short condition, the motor (or other load) could be shorted, so the load inductance might not present in the system anymore; the current in short condition can reach such a high level that may exceed the abs max current rating due to extremely low impendence in the short circuit path and high di/dt before oc detection circuit kicks in. So a ferrite bead or inductor is recommended to use the short-circuit protection feature in DRV83x2. With an external inductor or ferrite bead, the current will rise at a much slower rate and reach a lower current level before oc protection starts. The device will then either operate CBC current limit or OC shut down automatically (when current is well above the current limit threshold) to protect the system.

For a system that has limited space, a power ferrite bead can be used instead of an inductor. The current rating of ferrite bead has to be higher than the RMS current of the system at normal operation. A ferrite bead designed for very high frequency is NOT recommended. A minimum impedance of 10 Ω or higher is recommended at 10 MHz or lower frequency to effectively limit the current rising rate during short circuit condition.

The TDK MPZ2012S300A and MPZ2012S101A (with size of 0805 inch type) have been tested in our system to meet short circuit conditions in the DRV8312. But other ferrite beads that have similar frequency characteristics can be used as well.

For higher power applications, such as in the DRV8332, there might be limited options to select suitable ferrite bead with high current rating. If an adequate ferrite bead cannot be found, an inductor can be used.

The inductance can be calculated as:

Equation 1.

where

• Toc_delay = 250 ns
• Ipeak = 15 A (below abs max rating).

Because an inductor usually saturates quickly after reaching its current rating, it is recommended to use an inductor with a doubled value or an inductor with a current rating well above the operating condition.