so iam using a LMR16006Y Buck converter a 4-65V input to 3.3v output 600ma,iam a little confused with the choice of the output inductor.The Y version outputs @ 2.1Mhz the inductor iam looking at is the SRR1260A-121K which the test frequency shows 0.796Mhz.What exactly does this relate to?Do i need to worry about it?or iam i completely off base with going with this inductor?thanks
The test frequency is that frequency used to determine the Q of the inductor. The important parameter for a buck converter's inductor is the self resonant frequency (SRF) and, for this inductor is 5.5 MHz. It's a little close to the switching frequency for my liking - I tend to choose inductors that have an SRF that is ten times greater than the maximum switching frequency. Because the SRF is close to the third harmonic of the switching frequency you might get some strange (hard to pin-down) oscillations and noise on the output. Remember that the inductor is trying to block all switching noise in order to reduce ripple and above 5.5 MHz, this inductor will turn into a capacitor.
My gut feeling also tells me that a 120 uH inductor is not going to deliver much power when the input voltage is at the low end of the input voltage range you have stated (4 to 65 volts).