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BQ27542-G1: problem with using dummy battery

Chase Jeong
Genius 5440 points
Part Number: BQ27542-G1
Other Parts Discussed in Thread: TPSM53604

Hello TI experts,

my customer uses battery with BQ27542 and 18650(4.2V, 3500mAh).

and they also use dummy battery in case of there is not available battery. (dummy battery is made by 12V DC adapter and TPSM53604 buck converter)

they have no problem with normal battery. but when they use dummy battery they have a gauging issue.

voltage of dummy battery is fixed as 4.0V. but the capacity and percent status are differs from the situation.

(sometimes they can use long time with dummy battery, sometimes capacity is too small so they cannot use long time. even the system does not work because capacity is too low)

so my customer wants the capacity and percent status are fixed, so they can use permanently with dummy battery.

I think that there are some modifying points in settings of fuel gauge, but i don't know exactly.

here is the block diagram of normal battery pack and dummy battery pack, for your reference.

as you can see, the whole cell is changed to DC adapter and TPSM53604. rest of the part are same. and use HDQ for communication.

and the dialog below is one of the message that right after the insertion of dummy battery.

battery voltage is enough to use, but state of charge and remaining capacity is too low, so the system power down in a short time.

please check this issue, and let me know if there are any solutions, Thanks.

Best regards,

Chase

  • 0
    TI__Guru** 103235 points

    Hello Chase,

    Our gauges aren't really designed for this kind of application so it may require some extra work. If the reset() command is sent this will force the gauge to recalculate the SOC based on the chemID voltage lookup, so it should increase the SOC. If this is performed periodically it would maintain the SOC higher.

    Sincerely,

    Wyatt Keller 

  • 0 in reply to Wyatt Keller
    Genius 5440 points

    Hello Wyatt,

    My customer tested reset command with their product, it did not work properly. (SOC did not reset)

    they asked the way that fix all the values with same number on SOC table. (ex. fix all the values to same 80%, so the device read 80% SOC all the time)

    could you guide about this?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Guru** 103235 points

    Hello Chase,

    If the reset command is sent it should recalculate the SOC because the RAM is cleared and the gauge takes a OCV measurement to calculate SOC. The SOC cannot be fixed because it is calculated using FCC and RemCap which are outputs of the Impedance Track Algorithm. It may work if the disable IT so the gauge stops performing IT calculations. (IT_ENABLE command)

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Genius 5440 points

    Hello Wyatt,

    okay, i will check again about reset command what you said.

    and how can I disable IT? i know that to enable IT, i use the command 0021. how about disable? is there any command for it?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Guru** 103235 points

    Hello Chase,

    The command should toggle the IT_EN bit, so if you send the command while IT is active it will disable it.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Genius 5440 points

    Hello Wyatt,

    my customer tested the commands below;

    IT_EN -> reset (2 commands continuously)

    finally reset works. but it recalculate to SOC 0%. so we cannot use the battery properly.

    could you give me some advice for it? for example, recalculate to SOC 50%, not 0%.

    Please check this issue. Thanks.

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Guru** 103235 points

    Hello Chase,

    This is not an issue with the gauge, it is not intended to gauge a power supply. If you send a reset when the battery voltage is in the upper bounds it should recalculate SOC as higher. Can you send the .gg file and a log of the RESET command being sent with IT enabled?

    Sincerely,

    Wyatt Keller