I am trying to use this DC-DC converter and I am having trouble recreating the recommended circuit as I'm not entirely sure what an LDM is or where to find one: enter image description here

From basic google searches it looks like it's some type of inductor used in differential mode filtering, but when I try to find the component itself on websites like Digikey or Mouser, I'm coming up empty. It'll either be some massive part that costs hundreds of dollars or it'll be the full filter as a tiny SMD part, which I don't want. Can I use other types of inductors? Am I just searching for the wrong thing? (I've tried differential inductor and differential choke)

For context I'll be using 24 V for the input voltage and dropping it down to 5 V.

  • \$\begingroup\$ ”tiny SMD part, which I don't want” There is probably your problem. The industry has since long moved to SMD and so should you. \$\endgroup\$
    – winny
    Jun 10, 2022 at 14:05
  • \$\begingroup\$ @winny it's not really about the part being SMD (though it is more difficult, I can get over it) it's about these parts being pre-made filters that don't meet or fully define the specifications listed on the datasheet. \$\endgroup\$ Jun 10, 2022 at 14:38
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    \$\begingroup\$ I don't understand the problem. Digikey has 847 different 6.8 uH inductors in stock to choose from, 282 different 4.7 uF, 50+ V (ceramic) capacitors and 97 different Y-rated 1 nF capacitors. BOM cost for these < 1 USD even in small volumes. \$\endgroup\$
    – winny
    Jun 10, 2022 at 15:18
  • \$\begingroup\$ my question was asking if it could substitute with a regular inductor. What I'm having trouble finding is a differential mode inductor. \$\endgroup\$ Jun 10, 2022 at 16:53
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    \$\begingroup\$ You need to sort out the ones with too low Isat according to your max current. Link: digikey.com/en/products/filter/fixed-inductors/… \$\endgroup\$
    – winny
    Jun 10, 2022 at 17:11

1 Answer 1


You're making it seem more complicated than it is.

All two-port inductors are "differential mode" by definition. They can't be anything else: for common mode you need 4 ports at least.

LDM is just an inductor. The "LDM" label is entirely arbitrary, although it likely means \$L_{DM}\$: Differential Mode inductance. Any inductor with a suitably low series resistance, suitably high saturation current, and a matching nominal inductance will do.

Basically, any properly rated \$6.8\,\mu{\rm H}\$ choke will do. You need to know the operating current for the 24V input, and choose a choke with saturation current \$I_{SAT}\$ larger than the operating current, as well as maximum continuous operating current larger then the operating current. The former has to do with core saturation, the latter has to do with thermal heating of the coil winding.

When you find such a choke, the equivalent series impedance will be likely suitable for the application, so no worries there.


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