"Magic smoke" is an informal term used to refer to corrosive fumes from overheated electronic circuits and components. This phrase was spoken by almost every electrical engineer—usually when they forgot to adjust the power supply voltage level or accidentally short-circuited the voltage rail to the logic pin. The technical cause of the incident was electrical overstress (EOS); although human error is a common source, there are other possible causes and more subtleties. Some of the most common issues posted to the TI E2ETM Community Motor Drive Forum (including those beginning with "My motor drive has stopped working", "My motor drive was damaged", and "My motor no longer spins" The reason behind the problem is often EOS. Below I will briefly explain what EOS is and list the common root causes of EOS in the motor drive system. In the next article, the author will discuss several ways to help prevent EOS in the motor drive system. EOS is thermal damage that occurs when an electronic device experiences a current or voltage that exceeds the specified limits of the device. Thermal damage is generally caused by excess heat generated in EOS events (high current across resistance). This high temperature can damage the materials used to build the integrated circuit, causing its operation to be destroyed or permanently changed. Now that you understand what EOS is, how do you know what the limits are? To achieve this goal, you must carefully look at the absolute maximum ratings table in the electronic product datasheet (see Table 1, which comes from the DRV8701 data sheet). Absolute maximum ratings are such specifications - beyond which permanent damage can occur. In the data sheet, the absolute maximum ratings differ from the recommended operating conditions; if the technical specifications for those recommended operating conditions are exceeded, the device can continue to operate, except that it operates outside of the specifications of the product specification's recommended operating conditions. An example of a violation of Table 1 is if the VM power pin reaches 50V due to a transient event on the power rail... Table 1: Table of absolute maximum ratings of the DRV8701 So, what are some of the common causes of EOS in motor drive systems? Power overvoltage One of the most common sources of EOS is an overvoltage event on the input to the device power supply. Power overvoltage can be caused by motor regenerative power (as outlined in the previous article, see Figure 1 for an example) or external events in the system (such as component failure). Understanding the root cause of overvoltage events requires monitoring system power rails under all possible internal and external operating conditions. Figure 1: Power overvoltage transients Switching transients Another common source of EOS phenomena in motor drive systems is the voltage transients associated with the switching of power metal oxide semiconductor field effect transistors (MOSFETs). In an ideal half-bridge switching system, the voltage will alternate between VGROUND and VSUPPLY (Figure 2). But in the real world, parasitics in power MOSFETs and printed circuit board (PCB) layouts cause voltage transients—the voltage will go below VGROUND or above VSUPPLY (Figure 3). Figure 2: The ideal half-bridge driver Figure 3: Half-bridge driver with parasitics MOSFET overcurrent The last kind of EOS event that I will mention is related to the over-current of the power MOSFET. TI's integrated motor driver features over-current and over-temperature protection to prevent EOS in over-current conditions. I discussed these in detail in a previous article, but for systems using gate drivers (with external power MOSFETs), you must be careful not to violate the MOSFET safe operating area regulations. The power MOSFET datasheet usually contains a Safe Operating Area (SOA) graph (shown in Figure 4). Excessive current in the power MOSFET will eventually cause thermal damage to the device or its package. Figure 4: Maximum safe work area for CSD18540Q5B Kosta Small Power Generator,Home Use Power Generator,Kosta Air Cooled Portable Diesel Generaor,Kosta Small Power Generator Set Shanghai Kosta Electric Co., Ltd. , https://www.ksdpower.com