LM5164-Q1: Light Load Noise from Inductor

REDDY Y

Part Number: LM5164-Q1

I am using LM5164-Q1 to step down voltage from Vin (30V-60V) to 14V4. During light load condition(5mA) i observed acoustic noise from inductor which disappeared upon more load.

in our application load current varies from 5mA to 800mA.

1. Pls advise on avoiding noise

2. Will this noise cause EMI EMC issues .. Pls clarify..We Target to qualify CISPR25

over 3 years ago

0 REDDY Y over 3 years ago

Intellectual 850 points

0 Harrison Overturf over 3 years ago in reply to REDDY Y

TI__Genius 10665 points

Hello R Reddy,

What do you mean by acoustic noise? Do you mean there was an audible noise coming from the inductor at light load?

Or is this noise something observed on the oscilloscope? If so can you please capture a waveform and send it so I can take a look at it. Thanks.

Regards,

Harrison Overturf

0 REDDY Y over 3 years ago in reply to Harrison Overturf

Intellectual 850 points

Yes its audible noise coming from the inductor at light load

0 Harrison Overturf over 3 years ago in reply to REDDY Y

TI__Genius 10665 points

Hello R Reddy,

There is a high probability that the sound is coming from the capacitors around the inductor instead of the inductor itself, have a look at the following articles and blog posts:

https://e2e.ti.com/blogs_/b/powerhouse/archive/2016/08/09/how-to-reduce-acoustic-noise-of-mlccs-in-power-applications

https://www.edn.com/reducing-mlccs-piezoelectric-effects-and-audible-noise/

The following articles provide techniques to mitigate the audible noise from occurring on your PCB:

https://www.eenewseurope.com/news/improving-reliability-and-lowering-audible-noise-led-drivers/page/0/1

https://www.edn.com/reduce-acoustic-noise-from-capacitors/

Regards,

Harrison Overturf

0 REDDY Y over 3 years ago in reply to Harrison Overturf

Intellectual 850 points

Dear Harrison,

Thanks for the detailed links.

I would like to know the impact of Audible Noise on EMI EMC Test results . Pls clarify

However i will work on mitigating the Noise .

0 Harrison Overturf over 3 years ago in reply to REDDY Y

TI__Genius 10665 points

Hi R Reddy,

The frequency range of the audible noise is very low therefore it will not be attenuated significantly by your EMI filter which will result in lower frequency noise in the 20 Hz - 20 kHz range to appear during EMI testing. The energy of this noise will most likely be low and shouldn't cause a significant effect during EMI testing.

Regards,

Harrison Overturf

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LM5164-Q1: Light Load Noise from Inductor