 Welcome to ST Microelectronics tutorial on power MOSFET parameters. In this session, we will review common MOSFET parameters to the MOSFET absolute maximum ratings. Understanding the absolute maximum ratings is absolutely critical to ensuring the reliability of the device and the application. These are the extreme capabilities of the device and are never to be exceeded under worst-case conditions, otherwise the MOSFET may fail. The first parameter is the VDS or drain source voltage rating. It specifies the maximum voltage blocking capability of the MOSFET when the device is held off by lack of gate voltage, as seen by the VGS equals zero operational condition. This is the only parameter that may be slightly exceeded after consideration of the Avalanche capabilities of the MOSFET, which will be explained in more detail in another tutorial. The part is guaranteed not to Avalanche when operated at voltage below this maximum rating. Next, the VGS or gate-to-source voltage rating. The gate is the control terminal of the MOSFET, insulated from the drain-to-source conduction channel by a gate oxide. Exceeding the voltage rating of the gate may result in degradation of this oxide and eventually increase current leakage or full failure of the MOSFET due to dielectric rupture. While exceeding this value may not always cause failure, reliability within this bound is 100% tested and guaranteed. Before discussing the ID or drain current ratings, it's beneficial to discuss the total power dissipation rating, or P-TOTE, and the maximum operating junction temperature of the silicon. The MOSFET's performance limit, whether in switching frequency or current conduction, is often bounded by keeping the temperature of the internal die below the maximum operating junction temperature, or T-J. Reliability tests are done at this T-J limit and used to calculate the reliability of the part. Operating below this temperature is key to ensuring long life. The temperature of the die is determined by two factors, package or case temperature and internal power dissipation. The maximum power dissipation is typically specified assuming that the case temperature is held to a constant 25 degrees Celsius. Given this condition, we can use the T-J and thermal resistance RTH-J to see from elsewhere in the data sheet to calculate the P-TOTE. Since this parameter is dependent on thermal resistance, you may find separate values depending on the package of the MOSFET. The risk of exceeding this maximum power dissipation is to exceed the junction maximum temperature rating, which we know will degrade performance, reliability, and may cause permanent failure. Let's move back to the ID parameter, or maximum continuous drain current rating. This is derived from either the maximum power dissipation P-TOTE, which in turn was linked to maximum junction temperature, or in some instances the current carrying capability of the wires botting the MOSFET die to the leads of the package. As with the P-TOTE, you will often see different values specified by package type. Power dissipation can be calculated for continuous conduction by the current squared times the drain source resistance of the on-state device, or RDS on. So the maximum drain current is that which keeps the power dissipated below P-TOTE. As RDS on is a temperature dependent parameter, the maximum drain current may be specified at different operating temperatures. The calculation is summarized below. Non-continuous current is characterized as pulsed and is derived from the safe operating area, or SOA, of the device. This will be discussed in detail at the end of this presentation. As the MOSFET transitions from on to off, a voltage transition at the drain of the device occurs, the static DVDT. This can cause two unwanted phenomena to occur. First is a false turn-on. The fast rate of voltage change on the drain can induce a displacement current through the internal gate-to-drain capacitance, so as to pull the gate voltage above its threshold. This will cause the MOSFET to turn on into its linear region of operation, where power dissipation is very high. If the effect is strong enough, it may cause failure by exceeding the maximum allowed power dissipation. However, this being an effect of many external variables, it cannot be specified as an absolute maximum rating. The absolute maximum MOSFET DVDT ruggedness parameter is related to the turn-on of the intrinsic parasitic transistor. Much as the DVDT can cause a displacement current through the gate-to-drain capacitance resulting in the turn-on of the MOSFET at its gate, a very high DVDT can also put a displacement current into the base of this parasitic transistor through an internal capacitance. If this current is large enough, it will cause the bipolar transistor to turn on, resulting in a much reduced voltage blocking ability. This in turn makes the device subject to a dangerous avalanche breakdown. It is a particularly high-risk parameter in high-voltage MOSFETs. Diode recovery or dynamic DVDT is related to putting a voltage across the MOSFET while its body diode is conducting a current, such as is often found during soft switch commutation. There is an intrinsic body diode, which is an artifact of the parasitic bipolar transistor we just discussed. During current conduction through this diode, a high charge concentration is built up that must be removed for the diode to turn off and regain the voltage blocking ability of the MOSFET. As the diode transitions from conducting to voltage blocking, a DVDT on the diode occurs that causes displacement current in the parasitic capacitances, a peak recovery current, and simultaneous increase in voltage across the device. These combined stresses can result in failure. The diode recovery DVDT should be explicitly checked in all applications relying on the body diode for current commutation. The more rugged this DVDT absolute maximum rating, the more suited the MOSFET is for applications such as resonant or zero voltage switched bridge topologies. Finally, a discussion on the safe operating area, or SOA of the MOSFET, helps to tie together some of the concepts discussed related to the absolute maximum ratings. The SOA is a graphic always found near the end of the MOSFET data sheet. The drain source voltage is plotted on the x-axis and the drain current on the y-axis. Multiple curves related to the drain current pulse duration are graphed. Let us examine each section of this graph. First, note that the curves assume an operating case temperature of 25 degrees Celsius and a maximum allowed temperature of Tj is found in the absolute maximum ratings. Indeed, this curve is mostly related to maximum power dissipation akin to the way we derive the p-tote parameter. The vertical curve boundary here in green is dictated by the absolute maximum drain voltage rating and is independent of the drain current. The horizontal maximum overall drain current for pulse operation is graphed also in blue and equal to the absolute maximum pulse current, often package limited. To connect these boundary lines, we must derive a variable power dissipation limit, done by multiplying the static thermal resistance by the thermal impedance k-factor found in a separate data sheet graph shown here. The k-factor relates a reduction in junction to case thermal resistance dependent on the duty cycle and duration of the drain current pulses. In this case, we see that a single pulse lasting 10 milliseconds has a k-factor of 0.1. The shorter and or less frequent the pulse, the lower the thermal resistance and higher the power dissipation allowed. This power is calculated by multiplying the drain voltage and current together. The DC operation curve always comes from a k-factor of 1. Shorter and shorter pulse length curves are derived from ever shrinking values of k. Finally, the positive sloping curve in red is a practical limit to the relationship between the drain voltage and current related by Ohm's law. Voltage equals current times resistance, where the resistance is the maximum RDS on of the device at 25 C. Theoretically, the region above this curve is allowed, but not reachable in practice. That concludes our tutorial on MOSFET Absolute Maximum Ratings. Thank you for listening. For more information, please go to www.st.com.