SBVS343A March 2019 – September 2019 TPS7A78
PRODUCTION DATA.
The TPS7A78 uses a bulk capacitor C_{SCIN} 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 C_{SCIN} 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 C_{SCIN} capacitor required can be calculated using Equation 17 through Equation 20, however these equations make the following assumptions to simplify the C_{SCIN} capacitor calculation:
Use Equation 17 for the FB 60-Hz V_{AC} supply and Equation 18 for the HB 60-Hz V_{AC} supply.
Use Equation 19 for the FB 50-Hz V_{AC} supply and Equation 20 for the HB 50-Hz V_{AC} supply.
where
The calculated C_{SCIN} 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.