I want to know how they got the value 25.1kohm. what is the value of (In). they have not mentioned it. please check it. I am attaching the part of datasheet for your reference.

http://www.ti.com/lit/ds/symlink/lm3409.pdf

 

ln is the natural logarithm.

 

ln is the natural logarithm.

Oh OK OK. Ty sir. How much ripple current I can assume for laser diodes? Since they are very sensitive for spike currents.