DC/DC converters can be synchronized to a clock signal to improve system performance. Typically, if the device starts up before an external clock signal is applied, then the internal PWM oscillator frequency is set by the RFSEL resistor. In this scenario, a high impedance buffer can be used to isolate the clock to maintain the proper RFSEL detection when the clock is unused. This application note introduces how to provide this isolation using a simple AC coupled circuit instead of a buffer, and how to choose the corresponding component values to stay within the absolute voltage ratings of the TPS543620 device used in testing this implementation.
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