BQ24192I: Suppressing the 1.5Mhz noise

Hello,

You can review the schematic and PCB layout tips here: https://e2e-uat.ti.com/support/power-management/f/power-management-forum/877725/faq-bq24192-bq2419x-schematic-review-and-pcb-layout-design-tips

Can you also share your layout and scope captures of the VBUS, VSYS, and VBAT when the noise is present?

Sincerely,

Wyatt Keller

Hello Wyatt,

Please find attached the 3 scope captures of VBUS, VSYS and VBAT. Also attached are the gerbers for this PCB. Thank you for the application note but as I mentioned before, we have followed it to the letter.

Nir.

LED-A_GERBER.rar

Hello Nir,

Can you share an image of your schematic and layout so we can take a look quicker? From the images it looks like the capacitors may not be close enough to the charger causing the voltage to fluctuate. 

Sincerely,

Wyatt Keller

Dear Wyatt,

A PDF of our schematics was attached to my first post on this thread. The gerbers containing the PCB layout was attached on my last post.

Nir.

Can you open a BRD file? This will give you the best possible view of the PCB design

Hello Nir,

It would be easiest if you could share both so we can check if there's anything in the image/PDF first.

Sincerely,

Wyatt Keller

LED-A.brd

Hello Nir,

I couldn't see anything that looked like it may cause this kind of behavior, then only thing would be trying to increase the capacitance on the power paths where you have them already, and increasing some of the smaller trace paths from the PMID capacitor for example.

Can you explain the test conditions when you see this behavior? Does it occur all the time in any charge mode or only specific times?

Sincerely,

Wyatt Keller

Hi Again,

An update: I have found out that the inductor I was using was wrong. It could not carry the charging current. I have now replaced it with a bigger one and the VBUS signal looks great. BUT, that did not solve the SYS signal (see attached scope image) which still has 1V spikes on it.

The test conditions are: A 15V charging voltage is applied. A 2A current input limit is programmed but the actual current drawn from the power supply is about 1.4A so a total of 21W is applied. 

I am now thinking: Is this too much power to ask from the BQ to handle? The D/S states 4.5A charging current - I assume that's on the battery side so how do you calculate the charging power? Is it according to the max charge voltage of the battery (which is 4.2V resulting in 18.9W) or according to the nominal battery voltage which is 3.7V (then the max power would be 4.5A times 3.7V which is 16.65W)?

Nir.

I have gone ahead and lowered the charging power to about 10W. The noise is lower, but it is still there. It seems it is a common mode noise since I also see it on my GND path.

Can anyone help?