Shielded Buck SMPS power inductors close to each other on PCB is a problem?

[treez]

Hello,
We have three 150W Buck converter LED drivers next to each other on a PCB. (vin=48V, Vout=37v, iout=4A)
We are using the Wuerth 7447709330 33uH inductor in all three buck converters. They are lined up on the PCB alongside each other, 7mm apart. Do you think that their close proximity will affect their inductance value and give rise to saturation?

Wuerth 7447709330 power inductor datasheet:
https://katalog.we-online.com/pbs/datasheet/7447709330.pdf


Would the following alternative inductor (SER1390-333ML) be worse when placed as above, due to the opening in the core body? (we would not have the opening facing the neighbouring inductors)

SER1390-333ML inductor (33uH)
https://www.coilcraft.com/pdfs/ser1390.pdf

 

[andre_luis]

If no other interference effects are being perceived on each board circuitry itself, means the path of magnetic flux field is well confined on ferrite core, therefore mutual coupling between inductors placed at neighbor boards could be presumably negligible, in theory.

Anyway, it´s quite important to know the exact location of logic/magnetic main components at the board to check if such layout design encourage side by side arrangement.



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[treez]

You can see the inductors here....and for scale purposes , you can see the DPAK FETs near them, and some SOT23 transistors.

So do you think there would be reduction of inductance in these close together inductors?
Could we have these inductors literally right next to each other, with no gap inbetween them and still suffer no effects such as inductance reduction or saturation.?

 

[KlausST]

Hi,

i don´t expect a problem with the inductors.

**
from the picture i assume three independent buck regulators. The switching frequency of smps are asynchronous.

I expect that the three regulators sometimes catch the switching edge of the neighbour, then the output voltage may drift a little, after that they may loose the catching.
Therfore i expect an increased voltage ripple at the output. Maybe you recognize that the outputs jump some voltage step (100mV ??) around their setpoint.

If you see this effect, then you may try to run the three regulators in sync mode, if possible.


Klaus

 

[andre_luis]

Taking a look on datasheet above seems as this P/N has no gap, what means the electromagnetic field spreading around inductor tends to be quite minimized. Another point, if I understood correctly is that such core model seems to be a kind of pot, which have a good ability to confine magnetic flux path entirely on its structure.

Although must be avoided parallel placement of magnetic devices too close, my personal opinion is that on this case probably could no represent a big issue.



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[treez]

thanks but i'm not sure how you know that it doesn't have a gap?

 

[andre_luis]

I did not find any information about this on datasheet.

 

[BradtheRad]

The datasheet calls it a shielded power inductor. This suggests the flux field is confined within the component.

Anyway here is a way to test whether one unit will affect a neighboring unit. Place two of them close together. Run a brief 4A pulse through one, while you monitor for any sign of current in the other.

 

[andre_luis]

I may be wrong, but even considering a mutual interference level not negligible, the damping effect due to output capacitor added to closed loop control presumably would take care of this.



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