I am using a LMR16006Y buck converter with a 4-65V input to 3.3V output 600mA.

I am a little confused on the choice of the output inductor.

The Y version outputs @ 2.1MHz.

The inductor I am looking at is the SRR1260A-121K.

The test frequency shows 0.796MHz.

What exactly does this relate to?

Do I need to worry about it, or am I completely off base with going with this inductor?


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).

  • \$\begingroup\$ Ok perfect i wasnt 100% happy with the SRF either,but also the input voltages are going to 5-30V @400ma Max.I was just writing out the specs of the buck so you didnt have to click on the link. \$\endgroup\$ – user123646 Jun 21 '17 at 17:17
  • \$\begingroup\$ Do you think you can supply 600 mA to your load when the input voltage is 5 volts? \$\endgroup\$ – Andy aka Jun 21 '17 at 18:11

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