How to select the capacitor between Vin and Vout in LTC7149

Question

There's a 0.1uF capacitor between Vin and Vout in the typical application in LTC7149 datasheet, but it's not mentioned in the datasheet. And in demo board there're two capacitors, 1uF and 2.2uF. How to select the value of this capacitor? Is it necessary to add this capacitor between Vin and Vout, any advantage and disadvantage? 
 Thanks.

ADIApproved · Accepted Answer

Hi CSXXY, 
 These caps are necessary, but the value of this caps should be much lower than the one between VIN and system GND. 
 The purpose of these caps is to absorb high frequency voltage/current during the switching. However the value of these caps should be keeping low since it will form a voltage divider with Cout during input power up. You can use a single 1uF ceramic for this cap without problem.)

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How to select the capacitor between Vin and Vout in LTC7149