Regarding High Frequency Sound from iMX6 ULL SoM

Technical Support
,
1

Hello,
We are using Colibri iMX6ULL SoM,
MPN : 00361100

We have designed a board around it, When it is booted while mounted on our board there is a high frequency sound from the SoM.
But there is no such sound when it is mounted and booted on the colibri board, kindly help us out to address the issue.
[Below attached is the SoM Pinout in our schematics]
SoM SCH.pdf (2.7 MB)

Regards,
SUHAS S

2

Hi @suhas.s,

We quickly checked shared schematic, we didn’t find anything or at least it is difficult to say just from schematic from where issue is coming.
Can you write detail mail to support.in@toradex.com about issue.
Also please try to locate exactly which location you are getting this sound? Is this from module particular section or from baseboard?
Please also check your power supply is clean and as per module requirement mentioned in design guide.
Additionally if possible try to check with different module.
Please refer our design guide below
https://docs.toradex.com/102492-layout-design-guide.pdf

Best Regards
Ritesh Kumar

3

What is a source of your board 3.3V rail?
Can you connect a high bandwidth (100MHz oh higher) scope to that rail and check signal pulsation?

4

Hello @alex.tx and @ritesh.tx
Appreciate your reply, here is our response,

What is a source of your board 3.3V rail?

3.3V for powering the SoM is derived from Low Dropout Linear Regulator, This is how the 3.3V Supply is being derived:
230VAC to 24VDC [AC-DC SMPS]
24VDC to 5V [Buck Regulator]
5V to 3.3V [Low Dropout Linear Regulator]

Please also check your power supply is clean and as per module requirement mentioned in design guide.
Can you connect a high bandwidth (100MHz oh higher) scope to that rail and check signal pulsation?

Is 3.3V Line Clean? Here are the findings:

  1. When SoM is not connected on to the Base Board, [No Sound Issue] 3.3V line is Clean
  2. When SoM is mounted on the Base Board, and when SoM is not making any sound, 3.3V line is clean.
    [FYI : SoM doesn’t makes sound continuously, it makes sound stops in between starts once again, tone and pitch of the sound varies and the cycle repeats]
  3. When SoM is mounted on the Base Board and when SoM is making sound 3.3V line is noisy

To further check the power circuitry, we tapped 3.3V, 5V and Ground Lines from the Base Board and connected to Iris Board v1.1, X20 Connector, mounted the same SoM on the Iris Board, we observed there is no sound either on the Iris Board-SoM side or on the Base Board Side.
[Attached is the picture of the noise in 3.3V Line]

20220812_122316_HDR
20220812_122316_HDR1920×1701 283 KB

Also please try to locate exactly which location you are getting this sound? Is this from module particular section or from baseboard?

As it is a High frequency sound it is very difficult to pinpoint the location of sound, But as we have analyzed, we have strong reason to believe the Sound is coming from the 32.768 Crystal on the SoM.
[Attached is the Image encircling the area]

20220812_120539_HDR
20220812_120539_HDR1920×1333 302 KB

Regards,
SUHAS S

5

Hi @suhas.s,

Thanks for sharing information. Can you please also share power supply schematic. Is your power supply same as on Iris board or any other Toradex board if it is different I would recommend to get your power supply section reviewed properly.

  1. When SoM is not connected on to the Base Board, [No Sound Issue] 3.3V line is Clean

From your observation it seems like 3.3V is not clean under load. Something you need to check.

When SoM is mounted on the Base Board, and when SoM is not making any sound, 3.3V line is clean.

Do you know under what condition there is no sound? How often this happen? You can check CPU load and current consumption in both case to check 3.3V load.

Best Regards
Ritesh kumar