LTC3784 (LTC7841, etc.) Boost Capacitor value

Question

Dear Sirs 
 Datasheets for LTC3784 (p.23) and (at least) LTC7841 (p. 31) have note 
 " The value of the boost capacitor CB needs to be 100 times that of the total input capacitance of the topside MOSFET(s)." 
 But on all application schematic`s 0.1 uF capacitor is used along with top MOSFET`s HAT2169, RJK0652, RJK0305, BSC065N06. 
 Calculating max. MOSFET Input capacitance - 0.1uF/100 times = 1nF 
 MOSFET Input capacitance must be less then 1 nF for Cb=100nF. But for all listed MOSFET`s input capacitance much bigger. 
 Could you comment this, please? 
 -- Best Regards, 
 Victor

Fil · Accepted Answer

Hi Victor, 
 RENESAS RJK0305 typical input capacitance is 1.25nF. This is one that closest to the recommendation. In any case, those typical circuits in datasheet were built and tested with 0.1uF caps. You can try using larger CB cap when using bigger input capacitance FETs but we think there will be not much difference in performance.)

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LTC3784 (LTC7841, etc.) Boost Capacitor value