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bq27510-g3 min value of the standby current

Alexandru Mixich
Intellectual 495 points
Other Parts Discussed in Thread: BQ27510-G3, BQ27510, BQ24278, BQ24032A

hello,

i'm involved in a design where the reporting of the remaining capacity of the used battery is vital. So i've decided for this purpose to use a system gas gauge bq27510-g3.

I've understood mostly the function of the chip but i'm in doubt with the measurement of the standby current, respectively with the min. value of it. When our device is in OFF state the current consumption is less than 1 mA (ca. 300uA) from the battery. Because the device can remain in this state for a long time of period (i.e. 2 or 3 months) this fact can not be leave unconsiderated. I saw in the datasheet that a "deadband" value can be set in a range from 0 to 255.

If i set the deadband value on "0", will the bq27510 measure the OFF state current flow correctly?

How is the right dealing actually with this behaviour?

Thanks in advance for your help.

Alexandru

  • 0
    TI__Genius 14985 points

    Hi Alexandru,

    With Impedance Track fuel gauges you don't need to measure tiny amounts of current, and there could be considerable error in trying to coulomb count tiny currents due to calibration or offset error.  When the current is below the Quit Current threshold, the gauge will enter the relaxation mode and just use voltage measurements to update SOC. 

    Another reason this method is necessary is because of self-discharge within the cell.  The capacity will slowly drop over time due to "chemistry" and this loss of energy can't be coulomb counted because it's not current flowing through the sense resistor.

  • 0 in reply to dMax
    Intellectual 495 points

    Hi dMax,

    thank you for your reply.

    I have another question. I intend to use as a charger the bq24278. The Thermistor from the battery pack will be connected to the TS input of the bq27510. The /BAT_GOOD from bq27510 shold be connected to the Input TS of the bq24278.

    It will be possible to do this without any Problems?

    I've made a test but the behaviour seem's to be very strange

    If I connect the TS pin of the charger trough a 10 kOhm to GND and over a nmos Transistor the gate on /BAT_GOOD(like the app note for bq24032A) then the SYS Output of the charger will NOT have a constant value. The value drop down to 1-2 Volt so my buck/boost converter will not start poperly.

    Do you have any suggestions how to overcome this behaviour? (My Intention is to supervise the battery pack temperature over bq27510 to have also the possibilities to measure the OCV voltage of the pack during different situations)

    Alexandru

  • 0 in reply to Alexandru Mixich
    TI__Genius 14985 points

    Hi Alexandru,

    Do you mean you are following the example in Figure 4 of SLUA439?

    I don't foresee any problem with that, but I wonder if your circuit is biased properly for this function.