SNVSA47C February 2016 – December 2020 LM5165
An input capacitor is necessary to limit the input ripple voltage while providing switching-frequency AC current to the buck power stage. To minimize the parasitic inductance in the switching loop, position the input capacitors as close as possible to the VIN and GND pins of the LM5165. The input capacitors conduct a square-wave current of peak-to-peak amplitude equal to the output current. It follows that the resultant capacitive component of AC ripple voltage is a triangular waveform. Together with the ESR-related ripple component, the peak-to-peak ripple voltage amplitude is given by Equation 17.
The input capacitance required for a particular load current, based on an input voltage ripple specification of ΔVIN, is given by Equation 18.
The recommended high-frequency capacitance is 1 µF or higher and should be a high-quality ceramic type X5R or X7R with sufficient voltage rating. Based on the voltage coefficient of ceramic capacitors, choose a voltage rating of twice the maximum input voltage. Additionally, some bulk capacitance is required if the LM5165 circuit is not located within approximately 5 cm from the input voltage source. This capacitor provides damping to the resonance associated with parasitic inductance of the supply lines and high-Q ceramics.