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Power Supplies 101 Slide 32

The current limit of the SC418 is based off the low-side FET RDSON. The RDSON of the FET is first multiplied with the desired current limit, then divided by 10μA. The result is the resistance needed for RILIM. For this example, an RDSON of 5mΩ is used for the low side FET and a desired current limit of 20A is used. The result is a 10kΩ resistor for RILIM. The RDSON used in the equation shown here needs to include any temperature related effects as the RDSON can vary by 30% or more over the full temperature range. FET selection is based on a tradeoff between efficiency targets, cost and PCB area.

PTM Published on: 2011-09-27