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I'd like to add two AP6320x based DC-DC converters to small MCU board, for 3.3V and 5V. Since inductor is usually a critical component I wanted to do it right. Also, it would be nice to use inductors from same manufacturer and with same footprint.

The datasheet recommends 3.9uH and 4.7uH. I am doing a quick search on digikey and surprise - there are over 60 parts with 4.7uH, but only ONE with 3.9, from manufacturer I haven't even heard of before.

Not to worry, there is also a formula in datasheet. I am calculating for 20-30V input and (rather wide, IMHO) 30% to 50% suggested range of dIL and getting anything from 2.5 to 4.5uH. Sure, 3.9 falls somewhere in between, but there are almost no suitable inductors in this range either, other than 3.3uH, which seems rather small.

So, the question:

Am I correct in understanding that choosing somewhat (reasonably) larger inductor should not affect the function of the buck converter, other than reducing current ripple a little?

Because if that is the case I can go with two identical 4.7uH parts and be done with it.

Maple
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  • Use the formula in the data sheet rather than trust a schematic diagram that doesn't specify what the input voltage range. – Andy aka Sep 24 '21 at 08:39
  • Yes, it worked for me, "reduce ripple by using a higher inductance". It is in the datasheet, "Eq.7" & "Eq.8", – jay Sep 24 '21 at 14:24
  • @Andyaka , not relevant quest, I don't know where to ask, and thought you may know: When and why the upvotes (to my comments) do not update my score? – jay Sep 24 '21 at 14:28
  • @jay they don't add to or reduce your reputation score. Simple as that. The net comment upvote score gets sent to charities around the world!! – Andy aka Sep 24 '21 at 14:41
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    @Andyaka ha ha.. and thanks! – jay Sep 24 '21 at 14:47
  • @Andyaka that is exactly what I did (see 3rd paragraph). Regardless of how I calculate, I can only buy parts that are available, in this case either 3.3uH or 4.7uH. Hence my question, which I now highlighted. Basically - can I use 4.7uH inductor in place of recommended 3.9 or calculated 4.5? With global parts shortage I cannot afford to order the boards that won't work. – Maple Sep 24 '21 at 15:12
  • What does POL mean? – Transistor Sep 24 '21 at 18:27
  • @Transistor [point-of-load](https://www.maximintegrated.com/en/glossary/definitions.mvp/term/Point-of-Load/gpk/1016). Or closer to home https://electronics.stackexchange.com/q/231325/187920 – Maple Sep 24 '21 at 18:41

1 Answers1

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Well, I found an answer myself. Sort of. The Sparkfun COM-18357 board uses 4.7uF inductor. The Diodes' own evaluation board AP63203WU-EVM goes even higher with 6.8uH.

I guess what works for them should work for me too.

In fact, I think I can do better, as Diodes ignores their own layout guidelines and spreads components all over the board, while Sparkfun follows the guidelines but completely abandons any attempts at thermal dissipation.

Maple
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