Hi
Can someone help me to understand about switch current limit about Boost regulator. ?
Ex : MP3422
Data sheet : http://www.monolithicpower.com/Prod...ators/DC-DCPowerConversion/Synchronous/MP3422

Spec : Vin : 2V, Vo: 5.5V @5A

case 1 : Can MP3422 supports to boost 5.5V@5A from 2V @ 15A source , since the switch current limit is 6.5A.

Case 2 : How to decide whether Boost converter can deliver so much output current based on the switch current limit.

 

It says 6.5A at upto 5.5V out so thats 27.5W with 5A out, efficiency is about 90% at that current, so you'll need a 30W supply at 2V thats 15A.

 

The peak switch current in a boost converter is equal to the average input current plus half of the peak-to-peak ripple current in the inductor, which is usually selected to be about 20-30% of the average current.
Your average input current at 100% efficiency would be 5.5V/2V * 5A = 13.75 A
with 20% p-p ripple current you get to (0.2/2 * 13.75) + 13.75 = 1.1 * 13.75 = 15.125 A
and when efficiency is factored in at 90% it comes to 15.125/0.9 = 16.8 A.

The MP3422 is not even remotely adequate.

 

Thanks ebp, you mean switch current should be higher than the input average current (of 90%) plus half of pk to pk inductor ripple current . ?

 

Yes, that's correct.
Using 90% as the value for efficiency is just an estimate. With conventional rectification with low voltage output, efficiency my be less that 90%. With synchronous rectification efficiency might be greater than 90%.