BQ24170: Very high inrush current encountered when battery is plugged on to the PCB

Siddharth,

I can see your attached waveforms, but no schematic was attached.

Best Regards,

Ricardo

Hello,

Can you see the attachment now?

0552.Power Supply.pdf

Hi Ricardo,

I believe you will looking into my schematics today. I would like to share some additional experiment results and my understanding looking at the results.

The main issue that I am facing because of this peak current is that my battery is going into the protection mode quiet a few times when I plug the battery to my PCB. Just to make you understand my design in bit more detail, when I plug in the battery(note, there is no charging adaptor connected), the circuits which comes into picture are the battery charging circuit , the LDO U41, U18 load switch input side. U18 is main ON/Off switch of the device and all my other loads come to picture only when U18 is triggered by a push button event through U9. In nutshell, it is only the charging circuit and U41 which comes into picture when I plug in the battery.

Today I did the below experiments:

1. Measuring the rise time of the Vsys node when battery is plugged in. The waveform is added in yesterday's word file. It shos that the rise time is quiet slow and looks alright. It takes approximately 100us to reach steady state.

2. 2nd experiment I tried is to remove R315 and R316. This means Vsys node is disconnected to any other part of the PCB. So it is only the charging circuit which is active when battery is plugged in. With this , I still got the peak waveform which means the potential root cause hidden in the charging circuit itself.

My opinion is still that, it is the inrush current because of the capacitors which is causing this peak current.. Even after I removed  few caps on the VBAT/Vsys line, still the peak is same. You can have detailed look at the schematic and let me know your thoughts.

Do you think that the proper power on sequence shall be connecting the charger first and then the battery? Because it seems very obvious that if I suddenly connected a 12V battery to bare capacitors, they will pull current because of the transient effect. You can let me know your opinion on this as potential solution to this problem.

Looking forward to hear from you.

Thanks,

Siddharth

Seems like there is some issue in the attachment.

Hence Attaching once again the waveform file. 0535.waveforms.docx

Thanks,

Siddharth

Siddharth,

Your schematic looks good to me.

Experiment 1:Measurement of the peak current.

1. Since I do not have a current probe, to measure the peak current I replaced the fuse F1 with 0.5E resistor and tried to measure the drop across it while plugging the battery.

2. Attached is the waveform. The peak drop is ~6V which means the current peak is ~12A which is very high.

What happens if you remove BAV199?

2. One observation I had is if I remove the R296 which is series resistor with the gate of the PMOS, I still see Vsys node same as Vbat node when battery is plugged. I did not understood this. If the gate is floating, it can still conduct?

The body diode of the PMOS is conducting and allowing current to pass.

Best Regards,

Ricardo

Hi Ricardo,

Removal of Bav199 doesn't have any impact on the peak current.

I removed almost all the caps C267-269 , C273,C270 and C254 for testing purpose and checked the peak current.

The drop across my 0.5E sense resistor is ~3.32V to 3.75V which mean peak current is 6.5A to 7.5A . So there is a reduction from 12A.

What is your suggestion now? As in actual scenario, I cannot remove the caps. So do you think connecting adaptor and then connecting battery is proper power sequence?

I know there are other ways to counter inrush current like implementing soft start load switch or some kind to delay circuit. But I am restricted by space in my board. 

Thanks,

Siddharth