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Power Supplies 101 Slide 10

The datasheet states 10μF per amp of output current is needed to prevent the input to the regulator from sagging. To support the full current calculated on the previous slide, a minimum of 26μF is needed. Due to capacitor tolerances, a minimum 33μF capacitor should be chosen. In addition to the bulk capacitor, a 4.7μF ceramic is recommended to be placed directly next to the VIN pin of the regulator. For the output, the same rule of 10μF per amp of output current is recommended. This will lead to the same value of 33μF being used for the output. It is important to watch the ESR of the output capacitor to ensure the regions of instability are not entered. While a graph is not given for a 33μF capacitor, it can be interpolated between the two graphs given with the result being that a 5mΩ ESR should be used to maintain stability. It is also recommended to use a 0.1μF capacitor next to the VOUT pin.

PTM Published on: 2011-09-27