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Web Bench inductor Recommendation for LM43603

Other Parts Discussed in Thread: LM43603

Hopefully you can help me with something else regarding the LM43603. I used Web Bench as a starting point for my design, which is 12 to 30 VDC in (24 VDC nominal), and 3 amps at 4 VDC out. The inductor that web bench choose for this design is a Bourns SRR1280-220M. This part has an rms current rating of 4.3 amps and a saturation current rating of 4.1 amps. The data sheet for the LM43603 states: “The inductor current rating should be higher than the HS current limit” (This statement is found in the paragraph immediately following equation 16, in section 9.2.2.4 of the data sheet). The HS current limit of the LM43603 is about 5.5 amps, according to figure 25, which is clearly higher than either of the current ratings of the inductor. Is this inductor actually OK to use? The data sheet implies it isn’t.

  • Theoretically the inductor should be rated at least to the HS current limit, as stated in the data sheet.  However, this depends on the inductor saturation characteristics.  If the inductance value does not drop too much at 5.5A current limit, you may be able to use it.  You may want to check the saturation curve for this inductor if you want to use it.   This device has a hiccup type current limit that ismuch lower than the HS limit, so you may not every trip the higher value.  However, to be conservative,  you should select an inductor to handle the HS current limit as stated in the data sheet.

    I will pass this along to the apps engineer working on these products and also to the Webench team.

    FD

  • Additionally, WEBENCH gives you the option to size the inductor current rating based on the max Iout (of this application, 3A) or the device current limit (5.5A).  It is located on the left panel under Advanced Options: