BQ27421-G1: Best Practice when not using BIN pin

Hi Adam,
Pls review the quick start guide of the bq27421 or the TRM Your question is addressed in there.

In response to your question though, connect a 10K resistor from BIN to ground, and have your host inform the gauge when a battery is inserted. See the battery insertion section of the TRM for further details and let me know if you have further questions.

thanks
Onyx

Thank you for your prompt reply! I see there are many common questions addressed in the quick start guides. I do have additional questions, though:

What if the host does not have the ability to know when the battery is inserted/removed? How does a host typically acquire this information?

Adam J.

You have to come up with a way for your host to know a battery has been inserted. ..Perharps, the host being powered on, or a GPIO getting toggled....most users just use the battery thermistor...

thanks
Onyx

In my case, the battery is not likely to be removed except if the unit is sent back to the factory for service. So perhaps I could always assume the battery will stay connected?

However, I need to know what the worst case behavior is. If the battery is removed then reinserted but the battery insert command is not issued to the gauge, what happens? It becomes less accurate? And since removing the battery powers off the gauge, won't the gauge reset anyway?

Thanks,
Adam J.

Removing power resets the gauge. Your host will need to have non-volatile memory to store the your configurations and your qmax and Ra tables that get periodically updated incase there is ever a POR on the IC. Pls see the quick start guide of the bq27421 for further details on using these ROM gauges.

Yes, in that case if your battery is likely to not be removed then connect a 10k resistor from BIN to ground and set the BIE flag so the gauge always knows that a battery is inserted. The quick start guide discusses this. If the battery is ever removed, you will have to reload the image on the gauge. Again see the quick start guide for further details.
thanks
Onyx

Onyx,

If a fuel gauge is intended to be powered by the battery, and removing the battery resets the gauge, what is the function of the BIN pin?  It seems the gauge would not be operational when the "Battery Removed" command is sent to the gauge anyway.  What am I missing?

Thanks,

Adam J.

I'd appreciate more thoughts on this, as I'm not sure how to correctly use the BIN pin in my application.

Thanks,
Adam J.

The bq27421 is a "System Side" gauge. It can operate in systems that have an alternate power source aside from a battery. The BIN pin is used to detect if a battery is present in such a system. If the battery is not present, the gauge will not run its gauging algorithm (even though it is powered up).

.Dominik.

Ok, but the BQ27421's datasheet has a block diagram which shows it being powered from the battery pack, not the system voltage. Assuming I'm going to follow the recommended design in the datasheet, and I have a two-pin battery pack, does the BIN pin get used for anything at all?