SBVS343A March 2019 – September 2019 TPS7A78
The TPS7A78 uses a bulk capacitor CSCIN to smooth the rectified DC voltage ripple on the SCIN pin and to supply charge to the switched capacitor stage; see the 4:1 Switched-Capacitor Voltage Reduction section. The CSCIN capacitor also functions as a charge reservoir to hold-up the device output voltage for a period of time if the supply collapses. The minimum value of the CSCIN capacitor required can be calculated using Equation 17 through Equation 20, however these equations make the following assumptions to simplify the CSCIN capacitor calculation:
The calculated CSCIN capacitor from Equation 17 through Equation 20 represents the minimum value required for the application example. However, Equation 17 through Equation 20 do not account for capacitance derating for all operating conditions. Follow the manufacturer recommendation and guidelines to ensure the minimum required capacitance needed for the application. See the Input and Output Capacitors Requirements section for more details.