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Inductor on DCDC input filter

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  • Inductor on DCDC input filter


    I have this inductor for the DCDC input filter >

    It is a multilayer ceramic inductor "for high frequency circuits". The circuit I design is not HF but the filter is for removing HF, so I was wondering if I can use it.

  • #2
    It is 10nH. A 10mm long trace has about the same inductance...


    • #3
      Can you be more clear ? I don't understand. Phil uses a 10nH in his filter. I'm asking if I have to use a general purpose inductor or if I can use this RF inductor.


      • #4
        No, I cannot be more clear. You have the value from a schematic from Phil, but you do not share the schematic here. I do not know the schematic, nor his reasons to use that component.


        • #5
          You do not know the schematic ? it is in lesson 5 (Schematic Design - Power Supply) part 3 (Power Input filter (R-LC)), a sort of LP pi filter with 2x1u cap and 1x1n inductor for preventing HF (cutoff = 1.6MHz) passing from USB to LDO input. You can't see that in the course ? I was just asking if using a "HF inductor" was ok for that filter but I will figure it out myself. Thanks for your help.


          • #6
            I am not Phil nor have I done his course. So no, I do not know the schematic. I am just trying to help answer questions in this forum.

            But yes, if you want a cut off frequency of 1.6MHz and use 1uF capacitors (not taking DC and AC bias into consideration) you need 10nH inductance.
            The inductance curve in the datasheet starts at 10MHz, but it is fairly flat at the lower frequency. So it should be ok (in that aspect).

            Do keep in mind that most ferrite beads cannot handle peak currents. I do not know if this inductor (being a 0402) is any better in that aspect.
            You get peak current to charge the 1uF capacitor and all other capacitance behind it.