Therefore you can apply higher current than the specified package limit, if, perhaps you are able to maintain the MOSFET case temperature sufficiently cool, so that it remains under the maximum allowable thermal limitation value. The 50 amp value may actually signify that, if the FET current is exceeded above this value, the effects could be unpredictable, and this may possibly reduce the long-term reliability of the device. Meaning, if the MOSFET package is rated to handle 50 amp current, it doesn't mean that exceeding 50 amps, will suddenly cause an explosion of the device. Having said that, this current limit parameter is not actually a final limit. The package current limit, as we discussed earlier, depend on the true restrictions of the device package itself, and the internal chip connections between the silicon die and the plastic package or lead frame. We will start with the package current limit of the device.
Now let's understand all the above MOSFET current limitations with an in-depth detail.
And hence for sure, the thermal impedance of the device. For Texas Instrument T-0220 MOSFETs, for example, this is presented at 25 ☌, and also 100 ☌ case temperature.īelow this temperature level, there may be an additional continuous current rating, calculated with safe tolerance margins, with regards to the specific device's junction to ambient thermal impedance.Īfter that lastly, instead of a continuous current, we find a pulsed current rating included, which is, actually, calculated relative to both duty cycle and pulse duration. Other suppliers may possibly offer this at some different temperature level. Here, this is presented considering the device case temperature held at 25 ☌. Next comes the silicon current limit, which is characterized by the magnitude of current which the silicon die of the device can practically tackle, as soon as the MOSFET case temperature attains a specific value. Let's learn each of those parameters in greater depth.Īt the beginning, we see the package current limit, which signifies the limit characterized by the practical external limitations of the MOSFET package itself. Thus when we focus into our Absolute Maximum Table, we are able to see these are actually classified by 4 separate current limiting factors for the same device. Therefore each of these parameters may not be commonly relevant for every single MOSFET? To implement the current rating calculations, it is important to consider specific issues related to the circumstances which the device will likely be subjected to, for example the PCB assembly factor of the designer, the thermal surroundings etc. These are definitely not measured by an equipment, nor are these verified part by part during the production process. Which is the reason it's important to look at the footnotes wherever these are available, to know exactly where these ratings originated from.Īnother truly essential factor to remember is that, in any datasheet the transistor current ratings are just entirely calculated figures. The Current rating is perhaps the most deceiving parameter on a MOSFET datasheet, since you cannot find any industry standard technique to precisely evaluate this parameter.Īlthough there may be different approaches for estimating this, the descriptions can be apparently varied and misleading across different brands and manufacturers. In simple terms, MOSFET current rating can be defined as the maximum amount of current a MOSFET can handle safely and optimally across its drain to source terminals, with its case temperature held below 40 ☌. The post comprehensively explains the current rating of MOSFETs in their datasheets, and helps us to understand how it is calculated by the design engineers, keeping in mind the various external parameters, which potentially impact the current limitations of the device.
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