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bq20z65-R1: Operation without host?

John M
Expert 2135 points
Other Parts Discussed in Thread: BQ20Z65-R1, BQ78PL114, BQ3050, BQ20Z65, EV2400

Hello,

We have an application for a gas gauge that, for this first product, requires that it operate without a host. After reviewing the datasheet and the tech ref manual for the bq20z65-R1 it appears that we can use it this way. After programming the chip, can it operate as a standalone gauge and protector?

Our application is a 2S1P pack using Panasonic NCR18650B cells powering a small transceiver. Approximately 300mA continuous current draw with 1.5A-2.0A pulse for several mS every 30 seconds or so. SOC display accuracy can be +/-10%. 

The customer requires just a SOC display and cell protection for now (due to time limitations) but wants to poll the gas gauge for various data for the next version of this product. The bq20z65-R1 looks like it can be used for both versions.

Is there a different gauge that might be better for our application? Minimizing the amount of work required for production (programming, calibration, etc.) is important for our customer.

We also considered the bq3050 but it appears that its production workflow is about the same as the bq20z65-R1 and we have some experience with the bq78PL114 so we thought that sticking with an IT chip might be easier than jumping to CEDV.

Thank you!

  • 0
    TI__Guru* 76230 points

    hello John

    Based on your description, I would recommend you stick with the bq20z65. It has the functionalities that you described. It can work as a standalone gauge without host support. The 3050 can also achieve the 10% SOC but the production flow is almost the same as the z65. The z45 is a stripped down version of the z65 in that it doesn't have led support.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Expert 2135 points

    Hello Onyx,

     Thank you for the quick reply! We'll stick with the 20z65-R1 and order an EVM and EV2400 immediately.

    We've been thinking about reducing the number of production steps required for this first quick production run and I was wondering what the typical uncalibrated accuracy of the bq20z65-R1 was? Looking at the datasheet it appears that we could achieve our +/-10% SOC accuracy spec without calibration?

    Temperature range will be -10C to 45C and the packs can be occasionally cycled to empty and fully charged to force IT parameter updates.

    John

  • 0 in reply to John M
    TI__Guru* 76230 points

    Hi John,

    The bq20z65-R1 can achieve the +/- 10 % accuracy which you need without calibration. However, for customers who try to avoid calibration, we recommend taking 10-20 samples of your board, calibrate them, average the obtained calibration parameters in the gg file and use the obtain values in your golden gg file which will be used to obtain your golden dfi or ROM file.

    I believe you understand that at low temperatures, the capacities of batteries reduce significantly. Since the temperature range goes all the way to -10 deg C, I would recommend retaining the thermistor on there. However, an alternative will be to use the internal temperature sensor of the chip. This can be achieved by changing one of the configuration parameters in the data flash. Pls refer to the TRM for further info. It may not be as accurate as an external thermistor but it will suffice.

     

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Expert 2135 points

    Hello Onyx,

    Taking the average of a bunch of calibrated boards for the golden gg file is a great idea. We'll do that.

    Good thermistor recommendations. We'll be using a single thermistor nestled between the two cells, touching both.

    Thanks again!

    John