ZHCS614G October 2011 – September 2022 TPS40422
PRODUCTION DATA
The input capacitance is selected to handle the ripple current of the buck stage, when the high-side MOSFET switches on, while maintaining the ripple voltage on the supply line low. The input voltage ripple depends on input capacitance and ESR. The minimum capacitor and the maximum ESR can be estimated using the Equation 25 and Equation 26 because the input ripple is composed of a capacitive portion,VRIPPLE(CIN), and a resistive portion, VRIPPLE(ESR) . In this case, the allowed ripple for the capacitive portion is 0.1 V and for the resistive portion is 0.1 V.
For this design example, five 22-µF, 25-V ceramic capacitors and two 330-µF, 25-V electrolytic capacitors were selected in parallel for the power stage with sufficient margin. The electrolytic capacitors provide better stability during load transients by supplying enough current to the controller.