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Last Post 11 Oct 2013 10:50 AM by  steven.eckhoff
Article: Using the BQ27000 on DM3730 Torpedo SOMs Running Linux
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steven.eckhoff



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11 Oct 2013 10:50 AM
    This note will give you insight on how to use the BQ27000 on the DM3730 Torpedo SOM running Linux.

    BQ27000 Hardware:

    The battery fuel gauge a Texas Instruments (TI) BQ27000, requires 21V to program some of the registers for the best performance. If the gas gauge will not be pre-programmed during manufacturing:

    a. Ensure that the charger circuit will allow the BQ27000 to detect battery full. The default taper current for battery full is ~100 mA. The charger circuit must allow the charging current to drop below this threshold for at least thirty seconds before shutting off.

    b. For proper capacity measurements, ensure any battery starts fully discharged before attaching to the BQ27000. The default battery capacity for the BQ27000 is 2000 mAh. Values above 2000 mAh will be learned on the first charge cycle. Values below 2000 mAh will be approached over full charge/full discharge cycles, with a maximum decrease of 12.5% per cycle. The default battery discharge learning cutoff is 3.25V, where the BQ27000 assumes 6.25% of capacity remains.

    c. Refer to the TI BQ27000 product page for more information on this fuel gauge.

    Using the BQ27000 with the Linux BSP:

    On your host build PC perform the following:

    In the BSP directory with the LTIB script do the following at the command line to enter the LTIB configuration menu.

    $ ./ltib -c

    When the LTIB configuration menu appears, select configure kernel.

    Now exit and save the configuration.

    When the kernel configuration menu appears do:

    Add support for 1-wire device driver
    -> Device Drivers -> Dallas's 1-wire support <*>

    Add support for 1-wire master OMAP HDQ driver
    -> Device Drivers -> Dallas's 1-wire support -> 1-wire masters -> OMAP HDQ driver

    Add support for 1-wire slave BQ27000
    -> Device Drivers -> Dallas's 1-wire support -> 1-wire slaves -> BQ27000 slave support <*>

    Add support for BQ27x00 family
    -> Device Drivers -> Power Supply Class Support -> BQ27x00 <*>

    Add support for Generic PDA power driver
    -> Device Drivers -> Power Supply Class Support -> Generic PDA/phone power driver

    After building and booting the system with the new Linux kernel, there will be a new directory available at /sys/class/power_supply/bq27000-battery that contains access to the internal registers within the BQ27000.

    For example, to read the current voltage level on the battery do:

    DM-37x# cd /sys/class/power_supply/bq27000-battery
    DM-37x# ls
    capacity energy_now time_to_empty_avg
    charge_full power time_to_empty_now
    charge_full_design present time_to_full_now
    charge_now status type
    current_now subsystem uevent
    cycle_count technology voltage_now
    device temp
    DM-37x# cat voltage_now
    3798000
    DM-37x#

    The BQ27000 has specific requirements for learning the battery capacity. Please see the latest TI documentation and Torpedo Design Checklist for details.
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