8.2.2.1 Calculating the Cap-Drop Capacitor C_S

Use Equation 8 to calculate the minimum required cap-drop capacitance needed to support the application current. For common application conditions, Table 3 can be used to select the minimum standard cap-drop capacitor required to support the application current. However, neither Equation 8 nor Table 3 account for capacitance derating under biasing voltage and operating temperature conditions. Follow the manufacturer recommendation and guidelines on capacitor derating and degradation to ensure the minimum-required capacitance needed for the application under various operating conditions. Do not use a load current less than 10 mA to calculate the C_S capacitor because the device current is a larger fraction of the load current. Equation 8 and Table 3 can also be used to calculate the value of C_S depending on the application V_{AC (MIN)} voltage and frequency and then use the highest value for the application.

The capacitance value of C_S from Equation 8 is for the FB configuration. For the HB configuration, double the calculated capacitance value, then approximate the value up to the nearest standard capacitor value after taking capacitance degradation into account. Similarly, the capacitor value of C_S from Table 3 represents the minimum required capacitor value and is already approximated to the nearest standard value but capacitor degradation is not accounted for.