SBVS343 March 2019 TPS7A78
ADVANCE INFORMATION for pre-production products; subject to change without notice.
All the capacitors seen in Typical Schematic are required for proper operation of the device. For switching caps CSC1 and CSC2 , use the required capacitors values along with their voltage rating as specified in the Recommended Operating Conditions table. Oversizing switch caps is not recommended since it will have an adverse affect on the start-up time of the whole solution. It will also lengthen the time taken by the over-voltage clamp to recover from an over-voltage event. Keep the switch caps as close to the device as possible to eliminate any unwanted trace inductance.
For bulk capacitor CSCIN, use a minimum voltage rating of 35 V for CSCIN to account for bias voltage capacitor derating. As for CSCIN size, use Equation 4 for FB 60 Hz input AC supply and Equation 5 for HB 60 Hz input AC supply.
It is acceptable to round down the value calculated from the above equations to the nearest available standard capacitor value as long as it is with 10 % or less otherwise round up. It also recommended to oversize CSCIN and upscale its voltage rating to account for relatively low life expectancy especially when electrolytic capacitor is used. If your application requires a hold-up time, you can increase the size of CSCIN capacitor or CLDO_IN capacitor accordingly without exceeding the max CLDO_IN cap specified in the Recommended Operating Conditions table. Note that vastly oversizing CSCIN or CLDO_IN have an adverse effect on the startup time of the solution.
Use the minimum capacitors value specified in the Recommended Operating Conditions table if you application does not require a hold-up time. As for CLDO_OUT size, it is recommended to maintain 10:1 ratio between CLDO_IN and CLDO_OUT for application using close to maximum load current. For optimum device performance place capacitors as close a possible to the device.
|AC SUPPLY VRMS (Hz)||RS (min) (Ω)(1)||IOUT||VLDO_OUT (V)||CS (nF)||CLDO_IN (µF)||CLDO_OUT (µF)|
|FULL BRIDGE||HALF BRIDGE|
|120 (60)||68||10||3.3, 3.6, 5.0||100||220||10(2)||1|
|240 (50)||131||10||3.3, 3.6, 5.0||47||100||10(2)||1|