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mitigating failures

Common mitigation for these failure modes consists of the following. For the motor coil that is shorted or open case it is possible to monitor the current through the FETs and turn off the system if the current exceeds a predetermined threshold. In the case of the FET shorted, open, or damaged, monitor the current through the FET and the gate to source voltage. Once again turn off the system if the thresholds are exceeded. If the motor driver itself is damaged or has failed, one could monitor or add redundancies to the internal motor driver circuitry, or implement self tests on power up to catch any latent failures. With a suspected microcontroller failure, a watchdog integrated in the motor driver or the PMIC could serve the purpose of ensuring that the MCU is in the correct state. In the case of PMIC failure, once again a watchdog integrated in the motor driver could monitor the health of the MCU and reset the MCU if it browns out or is inactive. Another failure mode is changes in the original set up and configurations of the various components. Motor drivers are commonly configured at power up through software and it is important that their programmed state does not change. A mitigation for this would be to calculate checksums on the configuration setups and take appropriate action if the configuration changes inadvertently. These are only a few examples of common hazards and possible failure modes in these very critical automotive systems.

PTM Published on: 2016-06-07