Battery status using bq27500, OEM

Howdy!

I'm sorry this post got overlooked, but I'll try to answer now.

First topic: Is the bq27500 gauge the right one for your application?  Probably, but I'll throw out another option that might work depending on your system and its requirements.  Another good choice is the bq27210 which only has 10 EEPROM values to configure but still requires some knowledge and characterization of your battery and system to choose them.  It's simpler and gives fine accuracy for new cells if properly configured.  It does have compensation for temperature and load variations, as well as a gain age factor.  It's considered a Compensated End-of Discharge Voltage (CEDV) gauge since it counts coulombs passing in and out of the battery while watching for the EDV voltage, but compensating this voltage for temp and current.  The bq275xx family with Impedance Track algorithm has higher accuracy, however, and maintains this accuracy better even as the cells age, across varying loads, temperatures, etc.  Since it's accurately tracking the internal impedance of the cell it can take this factor into account and provide much higher accuracy for the life of the cells.  Of the IT-based gauges (bq275xx family) we now have several products.  The bq27500 is our original and requires an external LDO.  The bq27510 integrates this LDO into the IC.  We have a chip-scale package version of the bq27500 called the bq27505.  All of these bq275xx mentioned so far are designed to reside on the system board and monitor removable (or nonremovable) battery packs.  We also offer the bq27541 which goes inside the battery pack, integrates the LDO feature, and has a SHA-1/HMAC authentication feature if you want to confirm your battery is not counterfeit.

Questions for you:

a) First, please confirm if you are using a Lithium-ion battery chemistry and one series cell (about 3.7V nominal).

a) What is the battery configuration and capacity?

b) What is your system's typical load profile from the battery?  How often will you be drawing current from the battery, for how long, and how much?  What's the typical current draw?  What's the peak current draw?  Short spikes of current draw or steady pulls?

c) WIll you be recharging your battery or is it a primary cell?

Second topic: How to create a golden image.

Yes, you will need the bq27500 Evaluation Software (EVSW) and an EV2300 USB/I2C module.  The EV2300 can be ordered separately or is included when you order a bq27500 EVM.  The EVSW can be downloaded from the bq27500 product folder on ti.com.  If you go through the bqEASY wizard inside the EVSW it will guide you to create the golden image.  This can be done on a bq27500 EVM or on your custom board as long as you can communicate with the bq27500 by connecting the EV2300 I2C lines to it.  However, it's best if you do the calibration steps on some of your custom boards and then find out the average values from the dataflash, and use those averages in your golden image by manually entering them into dataflash during the golden image creation process.

Third topic: How to program the golden image into every bq27500 in production.

Two options:

a) Use the PC and EV2300 to program every system you produce.  You'll need to have a reliable connection to the I2C bus from the EV2300.

b) Most customers with high volumes use the host microcontroller to program the golden image into the bq27500.  We can take your golden image or DFI (binary) file and convert it to a text file that simply lists the I2C commands and data that the host will put on the I2C bus which will result in the programming of the bq27500.  Let us know once you reach this point and we'll get you going.

Fourth topic: How to read the battery status.

Yes, you can basically just send the I2C commands to read RAM or DataFlash locations.  The details are in the documentation, but we're also working on some sample code for the MSP430 and an app note that will be published next month.

Best regards,

David