BQ25886: Audible noise when charging at 3A

Jean-Baptiste Lancelin

Part Number: BQ25886

Hello,

I have audible noise during charging on my prototype board that is not present on the evaluation board under the same conditions (heavy load IIN = 3A). It's the second prototype already an we respected all layout recommendations. The final product is destined at the professional audio market and this kind of noise is unacceptable.

Do you have any idea on how to solve this issue?

Thanks a lot,

Jean-Baptiste Lancelin - VDB Audio

over 2 years ago

0 Michael Emanuel35 over 2 years ago

TI__Mastermind 41775 points

Hello Jean-Baptiste,

In order to evaluate this further we are going to need to know what and any differences that exist between your schematic and/or layout from our EVM? We also need to know specifically where the ringing is coming from, ie is it from the input side or the output side? I also am interested specifically in any difference between the input/output capacitors and the boost stage inductor.

Regards,

Mike Emanuel

0 Michael Emanuel35 over 2 years ago in reply to Michael Emanuel35

TI__Mastermind 41775 points

Can you also capture a waveform of the SW, BAT, charge current, and VBUS nodes when this is happening? Also SW, BAT, VBUS, and IBUS? Also SW, BAT, VBUS, and ISYS?

Regards,

Mike Emanuel

0 Jean-Baptiste Lancelin over 2 years ago in reply to Michael Emanuel35

Prodigy 10 points

Hello Michael,

The only difference is in the layout, and the fact that our prototype uses a type C USB socket. The capacitors and inductor were ordered using the BOM of the EVM board.

The ringing is happening at the input side (VBUS goes from 5.3V to 4.7V at a few kHz)

I'll send you the waveforms later today.

Regards,

Jean-Baptiste

0 Jean-Baptiste Lancelin over 2 years ago in reply to Michael Emanuel35

Prodigy 10 points

Here are the voltage waveforms. I don't have reliable ways of measuring currents on this board so I included VILIM measurements. I only have a 2 ch oscilloscope at my disposal so I plotted all traces against VBUS to keep the same time reference.

0 Michael Emanuel35 over 2 years ago in reply to Jean-Baptiste Lancelin

TI__Mastermind 41775 points

Hello,

It looks like you have VBUS and VILIM oscillating at 2.54 kHz which is in the audible noise range. If you notice your VILIM voltage keeps going up. Is your load oscillating? Can you check your system load?

Regards,

Mike Emanuel

0 Jean-Baptiste Lancelin over 2 years ago in reply to Michael Emanuel35

Prodigy 10 points

Thank you for the answer.

The ringing happens even with the load at "SYS" disconnected. As long as IBUS is set to be greater than ~2A there is oscillation.

0 Michael Emanuel35 over 2 years ago in reply to Jean-Baptiste Lancelin

TI__Mastermind 41775 points

Hello,

We are celebrating Good Friday. We will get back to you on Monday.

Regards,

Mike Emanuel

0 Michael Emanuel35 over 2 years ago in reply to Michael Emanuel35

TI__Mastermind 41775 points

Hello,

We need to analyze the charge current and input current to fully realize what is going on. It looks like your input may not be capable of providing the requested current, the supply crashes a little with current going up, and then it recovers again.

Can you provide a schematic?

Regards,

Mike Emanuel

0 Jean-Baptiste Lancelin over 2 years ago in reply to Michael Emanuel35

Prodigy 10 points

Hello Michael,

I would be more confortable sharing the schematics with you in private, if that is possible?

For info, the circuit is nearly identical to the EVM board.

Best Regards,

Jean-Baptiste Lancelin

0 Michael Emanuel35 over 2 years ago in reply to Jean-Baptiste Lancelin

TI__Mastermind 41775 points

Hello Jean-Baptiste,

You can friend me and send it there.

We still need to investigate why your power supply keeps drooping causing the input current to increase. Is there any other load on your power supply or is anything else connected to that input node? Getting waveforms of the input current and charge current are also necessary.

Regards,

Mike Emanuel

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BQ25886: Audible noise when charging at 3A