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Shown here are a few pieces of advice to get good results. As mentioned on the first generation PowerXR products, the total delay in the system is approximately 0.5 of a period. This means some phase boost is required. Although the high frequency pole is one way to increase phase, how much the designer can use it, is limited by the effect of the increasing gain. As such, at lower frequencies, having an output capacitor with 10-20 milliohms ESR is a distinct advantage to improve stability. As frequencies increase this need is eliminated. The XRP7724 with a quarter period delay has plenty of phase available. The modeling engine that generates the PID coefficients (compensation values) is only as good as the input. If bench results do not match simulation then the designer should consider measuring the components to ensure their values match those entered in the GUI.

PTM Published on: 2013-09-19