BQ34Z100-G1: Fuel gauge reset

Hello,

There are some updates to my original question as below. The .gg.csv file attached earlier was incorrect as the pack was sealed. I am re attaching the file and also the schematic this time.

1. In the scope plot I plot the REGIN, REG25, BAT pins of the BQ34Z100. I can see a 140mV drop on the REGIN. The frequency is 1 second and the on and off times are 880ms and 120ms respectively.

I have a fuse with a cold resistance of 6 ohm and a load switch with a on resistance of 1 ohm in series with the REGIN. The voltage drop indicates that there is a current slug of approximately 20mA every 1 second. Does this make sense?. is the gauge trying to calibrate something this often?

2. This slug causes a voltage drop of around 0.4V on the REG25 and it can drop as low as 2.1V. I believe this should be enough to cause a system reset like i am observing. The capacitor on the REG25 currently is 1uF. Can i increase this capacitor to 2.2uF ot 4.7uF?. will it cause any stability issues to the internal LDO?

3. Looking at the gg file is there any setting I can change to not have the chip consume so much current every second? is there any firmware update for this chip?

please see the schematic and the scope shots attached.

Thank you,

Gaurav

scope+GG+schematic.zip

Hi Gaurav,

Please scope REGIN to the device to ensure voltage being provided to the device is stable.

Sincerely,
Bryan Kahler

Hi Bryan,

Thanks for the response. I already have the scope plot of the REGIN included (please see in the zip file). The input to the load switch is the actual Li-ion cell which is fully charged and hence is at a constant voltage. The series resistance between the cell and the REGIN of the gauge is what is causing this voltage drop at REGIN (fuse 5ohm + load switch 10hm).

As per my calculations (0.16mV/6ohms) = 26mA should be the current draw. This current draw happens every 20 seconds or 1 second depending if the gauge is in sleep or not.

I currently have a 0.1uF on the REGIN and 1uF on REG25. is it OK if i increase the capacitance on the input and output as 0.22uF and 2.2uF respectively. I want to confirm that this has been done by others and there are no stability issues for the internal LDO.

Thanks,
Gaurav

Hi Bryan,

Internally the LDO output is connected to a POR circuit that gets activated if the output falls below 2.3V. I think when there is a current slug on the LDO and sometimes this droop can fall below this threshold. The POR range is 2.1V to 2.31V maybe that is why this is intermittent.

I changed the output capacitor from 1uF to 2.2uF and that improved the voltage droop from 2.1V to 2.4V and I don't see any resets anymore.

My question is that is this current slug expected?. is this because of some setting that i can modify and reduce the current?

Can increasing the capacitor to 2.2uF cause any startup or boot up issues foe the BQ34Z100-G1? any additional testing you propose i do before making this change for production?

Thank you,
Gaurav

P.S. is this a known issue?

Hello Bryan,

We have to release for production with this change to avoid any POR issues. Your expert opinion is highly appreciated.

Thank you,
Gaurav

Hi Bryan,

Is there any upper limit on the LDO output capacitor? In my case it seems like a 4.7uF on the output does the trick. is there any startup or stability issues with this value of capacitor that you are aware of?

Thank you,
Gaurav

Hello Bryan,

Thanks for the reply. can you consult with the design team if its OK to have this capacitor on the LDO output and if there are any side effects?

Thank you,
Gaurav

Hi Gaurav,

Looking into the issue. Please expect an update by COB Friday.

Sincerely,
Bryan Kahler

Hi Bryan,

Thank you for the confirmation. Appreciate your feedback and help on this matter.

Best Regards,
Gaurav