Difference in single cell gas gauges

Hi Matthieu,

Here's a long answer to your question, but I just wanted to give you an overview of the current landscape of our single-cell fuel gauge offerings.  I'm assuming you are looking at Li-ion/Li-poly rechargeable batteries in a single-series cell configuration.  If any of those assumptions were wrong, please let me know and we can try to point you in another direction.

The bq2620x are not full gas gauges but simply what we call battery monitors as they basically do raw coulomb counting.  You must then use that information in your own gauging algorithm.  This is usually a major project for someone to write their own.

The bq2650x are a step up from that in that the IC is a complete gas gauge solution that does coulomb counting, as well as takes voltage and temperature measurements, and then runs the gauging algorithm itself so you can directly read out things like State of Charge (SOC%) and RemainingCapacity (mAh).  However, even the bq2650x are quite old and I would recommend something newer to you.  The first upgrade from the bq2650x would be the newer bqJunior gauges, like bq27010 (HDQ) and bq27210 (I2C).  The hardware and algorithm are improved on these, and they remain quite popular but they are still not the latest and greatest.  Note that all of the products mentioned so far are typically embedded inside a battery pack.

If you are looking for a pack-side gauge, the latest offering would be the bq27742-G1 which runs the Impedance Track algorithm and also integrates the protector functionality.  For a standalone pack-side gauge without the protection function you could look at the bq27541-G1 (QFN) or bq27545-G1 (CSP).

If you don't want to embed the gauge in the pack, then you should look at some of the system-side gauges.  On the value side, the quickest and easiest to configure is the bq27621-G1 (no sense resistor, using the Dynamic Voltage Correlation algorithm).  Also, the bq27421-G1 (CSP with integrated sense resistor) and bq27441-G1 (QFN requiring external sense) do utilize a sense resistor and are equally easy to use.  No battery characterization is required for these, but there are other options for tuning the performance.  See the corresponding Quick Start Guides for each product for an overview of how they can be used, as well as flow charts for the host side interaction required.  We also have drivers for these gauges here:  https://github.com/aneeshv/linux-bq27xxx

On the more configurable side, I would recommend the bq27520-G4 (CSP) or bq27510-G3 (QFN).  Getting to production with the most accurate configuration would require slightly more effort than the '621 or '421, but they contain many more features and are the most flexible. 

Now, I'll leave you with some instructions should you require a driver for the bq275xx gauges.

Here are the details of a driver that supports bq27520.  It can easily be modified for any of our gauges.

The source code repository is here:

https://android.googlesource.com/kernel/omap/

Here is the command to clone it :

git clone https://android.googlesource.com/kernel/omap

I believe this is the latest branch:

https://android.googlesource.com/kernel/omap/+/glass-omap-xrt73b

Here is a direct link to the driver file:

https://android.googlesource.com/kernel/omap/+/glass-omap-xrt73b/drivers/power/bq27x00_battery.c

And here is a sample board file that instantiates the gauge I2C device.

https://android.googlesource.com/kernel/omap/+/glass-omap-xrt73b/arch/arm/mach-omap2/board-notle.c

Here is a tool created for flashing bqfs/dffs files to our gauges from Android.

https://github.com/aneeshv/bqtool

You can clone it by using the following command

git clone git@github.com:aneeshv/bqtool.git

Please read the README in the repository for further instructions.

Hello dMax,

Thank you for your answer.

Actually, the gauge I'm looking for is NOT for single cell, and not specifically for Li-Ion. I posted a few weeks ago on this topic, but got no answer. Let me explain again:

The new UPS for motion picture sound carts we're designing will have to run either on batteries we're currently designing (Li-Ion and LiFe) which will integrate a BMS with a gauge (probably a bq40z50 for many reasons), and will "talk" to the central unit via SMBus protocol. This far, no problem.

But we want our system to be also compliant with third party batteries that are not equipped with SMBus. So we are looking for a stand alone Coulomb counter on the system side that could give the user - after a full to empty discharge - an estimate of what's left in the battery. This Gauge (or simple Coulomb counter) will reside in the central unit, and communicate with the MCU (via HDQ or SMBus) which in turn will display the relevant info to the user.

We also intend to be able to run on SLA batteries, as those can easily be found on any shooting location all around the world (Papua New Guinea, for instance) in case the Lithium batteries got delayed because of the air carrier (IATA doesn't make any difference between Li-Ion and LiFePO4, even if the latter are much less prone to catching on fire! 100Wh is the maximum allowed in the luggage if no special precaution is taken).

So the ideal system side gas gauge should be able to handle any chemistry, as far as the user declares it and declares the nominal capacity.

The only product I found is bq2060A, but it's bulky, pretty old, needs an EEPROM to work along with and is intended to be on the pack side. That's why I was considering bq2650x, even if information wouldn't be as accurate as with a pack side gauge running Impedance Track or even CEDV algorithm.

If you have any suggestion, I'll be glad to hear from you.

Thanks for reading til here.

Best Regards.

Matthieu

You might check out the bq34z1xx family, but if you just want a raw coulomb counter to get an idea of how much charge has left your battery, then a "battery monitor" might do the trick.  However, the best IC we have that gives you access to raw coulomb counts would be one of the bqJunior gauges like bq27000, bq27200, bq27010, or bq27210.  There is an app note entitled "Building a Superior Battery Monitor with the bq27x00 " that would apply to any of these four.