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LMR51606: LMR51606YFDBVR inductor selection for 300mA output current at 5V DC.

Pavel Stambul
Prodigy 10 points
Part Number: LMR51606


Tool/software:

Hello.

We are planning to use the LMR51606YFDBVR chip to generate 5V voltage with a maximum current of up to 300mA.

To check the selected components I used WEBENCH. (Maximum) Parameters:

Input: DC 18 V - 42 V
Output:5 V at 0.3 A
Temp:80 °C

(LMR51606DBVR WEBENCH IC model used for calculations).

And for inductor parameters model recommends such selection criteria.
Recommended Limits:

L: 20.45 μH - 29.54 μH
DCR:10 mΩ - 416.7 mΩ
IDC:1.56 A - 6.5 A


The dimensions of the 22uH 1.56A (or higher current) inductor are quite large. It doesn't look like it's de-rating if I reduce the max temperature.
I don't quite understand where the minimum current of the recommended inductor 1.56A comes from when the required output current is no more than 300mA.
Can I choose an inductor with similar characteristics, but with a maximum current of up to 1A, for example?
Thank you in advance!
  • +1
    TI__Mastermind 31315 points

    Hi Pavel,

    Usually a good rule of thumb is to pick the inductor with a saturation current larger than the peak current limit of the device. The reason for this is to prevent damage to the internal FETs in the case of over current and the inductor saturation. 

    With this in mind, the peak current limit is 1.9A, so I would pick a saturation current around that. 

    Thanks,

    Richard 

  • 0 in reply to Richard Fu22
    Prodigy 10 points

    Hello Richard.

    Thank you for explanation.
    IHS_PK(OC) High-side peak current limit for LMR51606 is 1.4A max.
    Chapter 7.3.6 Overcurrent and Short-Circuit Protection sheds some light on your explanation.

    Indeed, it becomes clear where such a high value of the inductor current could come from with a maximum load current consumption of 300 mA.

  • 0 in reply to Pavel Stambul
    TI__Mastermind 31315 points

    Hi Pavel,

    Glad I could help resolve your issue. Thank you for using our device in your design. 

    Cheers,

    Richard