BQ25895 Battery Level

Hello John,

To add to Jeff's comments, I would like to add the following:

It depends on how accurate you need the state of charge to be reported. Also, are you looking to report state of charge only during charging? The ADC on the bq25895 only reports charge current, no discharge current is provided.

While the bq2589x family of devices provide battery voltage and charge current data, these would work if your application doesn't need a very accurate state of charge and you can implement some sort of crude voltage-based gauging in the charge direction, e.g. at 4.2V, your host processor would report 100% etc. Also, depending on the implementation of your gauging algorithm, it might take a toll on your host's processing capabilities/power consumption requirements. If your application can get away with this, then you can definitely follow Jeff's instructions on how to gather the data from the charger ADC.

Challenge with this approach is that the battery voltage is dependent on the current flowing through the battery and the fact that as the cell ages, its internal impedance will increase as well, affecting voltage measurements as well.

Have you reviewed our fuel gauge solutions? Can you share more details on your application?

Hope this helps.

FERNANDO/JEFF,

THANKS FOR THE DETAILED RESPONSE!!!!

I'm mostly interested in the State of Charge when its in normal use, so discharge mode. For crude purposes, is it reasonable to use 4.2v as 100% and 2.8V 0%? 

Our product is a bluetooth based sound system. Its using 6 different TI chips right now. I have looked over the gauging chips and if we thought is was really important, we would implement a more sophisticated approach. I don't want to rev the PCB again, so I was hoping there was some capability I could draw from.

In fact, our main processor has a battery charger capability built in, but we wanted better capacity/charge currents, so we use your chip offline. There is a monitoring capability built in that I can also just hook to the battery to and let the built in capability report the state of charge.

Any other thoughts would be appreciated.

John

Thanks, I will do that.

Last question. Is there any energy usage penalty by keeping OTG pin HIGH? Same thing for CE pin being held LOW? In the datasheet it shows these pins going to the controller with I/O and I just want to make sure its ok to just wire them permanently.

Hello John,

You can pull-up the OTG pin to REGN using a 10kOhm resistor if you don't wish to use the host to control the pin. Same applies for the CE pin, but pulling it down to enable charging.