Hi,

I am designing with Buck boost converter with the following parameters:

Vin: 2.5 - 4.2 V

Vout: 3.3V

Iout Max: 1A

Fsw: 1250Khz (From Dtasheet Page 3)

Mine is a battery powered application.

The inductor design calculation in the datasheet is given below.



I believe the 0.3A is the allowed ripple current.Please correct me if I am wrong.

The datasheet also says the below thing.


When I plug my values in the above equation I am getting L1 = 1.89uH and L2 = 1.62uH.




I have 2 Questions:

1. May I know where I went wrong.
2. How they obtained the recommended value of 1.5uH to 4.7uH

 

You might be just fine. Your values are within the stated range. You may have jumped to the conclusion that the formulas covered the range, but maybe the range was determined via another method.

 

Okay ,Why they select 2.2uH

 

It might be that they did experiments with a range of inductor values and those numbers represent empirical results. The value 2.2μH might represent, in the opinion of the experimenters, the best overall compromise given a number of different factors.

 

Many people here don't get a high enough current inductor. I looked up the coilcraft inductor LPS3015 2.2uH and it saturates at 2.1A. Don't get a 1A inductor.