SM72442: Inductor size in SM3320 reference design

Noman Bashir6

Prodigy 130 points

Part Number: SM72442

Hello Everyone,

I hope everyone is fine. I am trying to modify the "AN-2122 SM3320-RF-EV Reference Design" for one of my projects.

However, I have conflicting answers to the inductor size for this design.

1) One previous post about SM72442/5 says 20uH with 20A ratings.

2) The bill of materials says it is 27uH with the EFD-30 core but no current ratings are mentioned.

3) The bill of materials in application note states it is 2uH again with no current ratings.

Can anyone please comment on the exact size of the inductor used in the design?

Also, if I can use any other inductor with slightly different ratings for this design?

If yes, what should be the ideal range of inductor size that would work fine with this design?

Also, does it has to be EFD core or any other assembly would work fine?

I would highly appreciate a prompt response. Thanks in advance.

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru* 78220 points

The SM3320 uses two inductors, one for high voltage version (lower current) and one for low voltage version (higher current). For the high voltage version the inductor is 30uH, and for the low voltage version 20uH. These are nominal values and after full load dc bias the inductance can drop a little. Other inductors close to these originals should also work. You don't have to use the EFD core.

0 Noman Bashir6 over 7 years ago in reply to Youhao Xi

Prodigy 130 points

Hi Youhao Xi,

Thanks a lot for the response. I believe you are referring to the two inductors, L4 and L1. The L4 inductor is used to create a 10VDC power supply, which is mentioned as 220uH on application notes. The other inductor is L1 used in DC-DC buck-boost converter and have different ratings written at different places.

However, as you suggested, I should use 30uH and 20uH for L4 and L1 respectively. Is that correct?

This is the reference design I was talking about: www.ti.com/.../snosb76c.pdf. I just want to make sure before I order the components.

0 Youhao Xi over 7 years ago in reply to Noman Bashir6

TI__Guru* 78220 points

Sorry I misunderstood you. I just referred to L1. L4 should be 220uH or something close. L4 part number that we used on the design is: DR74-221-R from Coiltronics (currently Eaton?). Hope this clarifies.

0 Noman Bashir6 over 7 years ago in reply to Youhao Xi

Prodigy 130 points

Thanks for the clarification. However, I would appreciate if you could refer to high voltage versions and low voltage version for the SM3320 design. I could find only one and not sure which of the two versions is it.

0 Youhao Xi over 7 years ago in reply to Noman Bashir6

TI__Guru* 78220 points

The LV version usesL1=20uH and all input and output capacitors are 50V rated . The HV versions uses L1=30uH, and all input and output capacitors are 100V rated. The two versions share the same PCB and rated at the same power, just different in current and voltage in the main power stage.

0 Youhao Xi over 7 years ago in reply to Youhao Xi

TI__Guru* 78220 points

I just checked the document that you referred to. It is the LV version.

0 Noman Bashir6 over 7 years ago in reply to Youhao Xi

Prodigy 130 points

Thanks a lot for the clarification.

Power management

Power management forum

SM72442: Inductor size in SM3320 reference design