BQ25792: BQ25792 circuit emits audible noise during charging

Hi Keith,

At what input voltage, input current, battery current, battery voltage is this happening?  If at light load, is PFM enabled?  If out of audio enabled?  If not at light load, can you send a scope plot of SW1, SW2, SYS and VBUS, zoomed in to show the square-ish waveform of SW1 or SW2?

Regards,
Jeff

Hi Jeff,

Thanks for the quick reply.

Input voltage is 13V.

Battery voltage = 9V

Charging current = 1A

Is this considered light load?

All internal register at default settings; we just take /CE low.

Thank you for alerting me to the PFM operation. We will play with PFM_FWD_DIS and DIS_FWD_OOA to see if we can resolve this issue.

Thanks!

Hi Keith,

I would not expect the converter to be PFM with 1A charge current with those voltages.

Regards,

Jeff 

Hmm, OK, what else could it be?

Hi Keith,

Can I get a copy of the schematic and board layout as well as the scope plots mentioned above?

Regards,

Jeff

How do I attach files? What format for the files? Scope plots are difficult to get at this time.

Hi Keith,

Insert then Image/video/file then upload.

Regards,

Jeff

Battery Charger Schematic Sheet.pdf

Here is the schematic. Let me work on the layout next.

Here is the layout for the battery charger region.

BATTERY CHARGER LAYOUT.pdf

Hi Keith,

I don't see any obvious error with either the schematic or layout.

Regards,

Jeff

Thanks for the review. IS there anything else that could cause audible ringing? What if it is switching between buck and boost modes?

Hi Keith,

I have not seen that occur.  I need the scope shots to better diagnose.

Regards,
Jeff

OK, that's going to take a little effort to rig that up. I will send you the plots when I get them. Might not be for a while as I am on vacation next week. Thanks for all the quick responses.

In the meantime, I will modify an EVM with a 2.2uH inductor and test with

Input voltage is 13V.

Battery voltage = 9V

Charging current = 1A

Do you have any load on SYS?

Regards,

Jeff

No load on SYS.

Keith