Minimum inductor value for DCDC converter?

RE: Minimum inductor value for DCDC converter?

Jaison — Wed, 17 May 2017 05:02:04 GMT

Thanks for your replay. We did come across the third link, from coilcraft but the online source showed a high price.

RE: Minimum inductor value for DCDC converter?

AmbystomaLabs — Wed, 17 May 2017 04:06:00 GMT

Thanks for feedback on your design requirements. Quite the interesting little dilemma you have there. There aren't a lot of low profile chip inductors in the 2.5 to 10uH range. But I did a little thumbing around and found a few options. Oddly, they are all at Mouser. Apparently, the other vendors are falling behind. I should point at that although some are rated at 10mA, this is mostly a heating spec. The duty cycle, ambient temp and voltage difference between VDD and DEC4 will all decide whether or not this is sufficient. The more important aspect is staying away from saturation and the SRF. As Sigurd pointed out if you depart from the spec 10uH, ripple and stability will suffer. But you can always place 4 x 2.5uH. Enjoy!

www.mouser.com/.../JELF243B-9120-1102059.pdf www.mouser.com/.../AIML-0402-13956.pdf www.mouser.com/.../xfl2006-270679.pdf

RE: Minimum inductor value for DCDC converter?

Jaison — Wed, 17 May 2017 02:30:05 GMT

We are using WLCSP package. Maximum height we can allow inside the casing is 0.6mm.

RE: Minimum inductor value for DCDC converter?

AmbystomaLabs — Tue, 16 May 2017 13:18:17 GMT

Good point.

RE: Minimum inductor value for DCDC converter?

Sigurd — Tue, 16 May 2017 12:52:13 GMT

Could be that he's using WLCSP packet where the height is ~0.375 mm

RE: Minimum inductor value for DCDC converter?

AmbystomaLabs — Tue, 16 May 2017 12:44:17 GMT

I just thought I would point out that the nominal height of an 0603 inductor (ie, the 10uH) is 0.8mm whereas the nominal height of the nRF52832 is 0.85mm.

So, there is no savings in profile height by going with a smaller package inductor.

RE: Minimum inductor value for DCDC converter?

Jaison — Tue, 16 May 2017 09:07:32 GMT

Thanks for your confirmation.

RE: Minimum inductor value for DCDC converter?

Sigurd — Tue, 16 May 2017 08:58:41 GMT

If you cannot ensure that the total inductance is ~10 uH in the DCDC feedback loop, I would have to recommend that LDO mode is used.

RE: Minimum inductor value for DCDC converter?

Sigurd — Tue, 16 May 2017 08:57:18 GMT

Hi,

It might work with a slightly lower value, but it is not something we recommend and it will be outside the specification of the chip and can make the DCDC converter unstable.

A solution can be to use several smaller low-profile inductors in series, making it ~10 µH in total. E.g. you can use 3 low-profile 3.3µH in series to obtain the correct inductance.