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BQ25792: bq25792 as fuel gauge

Abhineet Ranjan
Intellectual 635 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ40Z50, BQ34Z100-R2

I am using bq25792 as BMS, can we use bq25792 as fuel gauge also along with BMS.
If Yes how can we measure battery percentage while charging and discharging.

If NO, can you recommend any fuel gauge in small form factor (battery capacity 12000mAh) which can be connected with bq25792.

thank you in advance

  • 0
    TI__Guru**** 166826 points

    Hi Abhineet,

    The charger's ADC only measure instantaneous voltages and currents.  It has no memory so can't perform gauging functions.  You could write host software to perform gauging function but buying a gauge is simpler choice. 

    I am moving this post to the fuel gauge team so they can get more info about your end application and choose the correct gauge for you.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 635 points

    I am using the driver code provided by TI, can you help how can I configure its input power voltage , battery charging voltage and output voltage for system.

  • 0 in reply to Abhineet Ranjan
    TI__Guru** 105760 points

    Hello Abhineet,

    The BQ40Z50 would most likely be the best gauge for your application if it is within 1-4s and needs cell balancing/protections. If you only need gauging and no individual cell monitoring/protection you can look into our top of stack gauges like BQ34Z100-R2.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Abhineet Ranjan
    TI__Guru**** 166826 points

    Hi Abhineet,

    The minimum input voltage for the VINDPM feedback loop is auto set at power up so no need to change unless the input voltage starts high and then drops low but not below chip UVLO (3.6V).  The PROG pin sets the battery regulation voltage (REG0x01-02), CELLS setting (REG0x0A[7:6]), minimum system voltage (REG0x00[5:0]) and default charge current (REG0x03-04).  When input power is applied, V(SYS) = higher of minimum system voltage or battery voltage.  While you can change any register after power up, you likely will only need to change the charge current register using the driver. 

    Keep in mind that the input current limit is set as the lower of the value set by the ILIM_HIZ resistors, if the EN_LIM bit = 1 (default), or the value determine by the D+/D- detection.  If D+/D- pins are left floating or shorted together, the D+/D- detection results in the highest setting of 3A.  You may need to change the input current limit via the driver.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 635 points

    I am able to charge the battery under default condition, but what are the changes required to dischage my battery to system when external power is not present. 

  • 0 in reply to Abhineet Ranjan
    TI__Mastermind 40525 points

    Hello,

    Please see Section 9.3.3, "If only battery is present and the voltage is above UVLO threshold (VBAT_UVLOZ), the BATFET turns on and connects the battery to the system."

    Regards,

    Mike Emanuel