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BQ25790: Simple use of BQ25790 to charge a 3S 3P battery

Martin Lindsay
Prodigy 10 points
Part Number: BQ25790
Other Parts Discussed in Thread: BQ24179, BQ25792, BQ25798, BQ25720

Hello,

I would like to incorporate the BQ25790 battery charging IC in a new design, and I have some questions as follows:

The battery I would like to charge is an Ni2020HD29 which is a 94 watt-hour 10.8V 3S 3P smart bus device. Should the BQ25790 be capable of accommodating this battery?

The design will have a processor which will use I2C bus to interrogate the battery status. Can I do this just using the I2C clock and data lines, and let the BQ25790 perform its charging autonomously?

If the BQ25790 becomes unavailable, can the BQ24179 be used in its place?

I will need to limit the max charging current to 4A. Is this a relatively simple thing to do?

The device may be in storage for a long time with the charging source removed, and the processor powered down. Would you advise using ship mode / shutdown to conserve battery power? Can the BQ25790 be easily restarted when the processor is restarted?

Another device I am interested in using is the BQ25792. Would this be suitable, and is there is similar (identical pinout) device that I could use if this became unavailable?

 

Best regards

Martin Lindsay

Ocean Technical Systems

  • 0
    TI__Guru**** 166626 points

    Hi Martin,

    The BQ25790 (or BQ24179) can perform 4A charging of 3S LiIon battery.  The charger can charge at the default settings VBATREG=3x4.2V=12.6V and ICHARGE=1A without host but will need the host at least briefly after power up in order to change and retain non-default settings in I2C registers.

    Shutdown mode results in the lowest battery Iq consumption because it disables I2C communication.  Shipmode requires slightly more Iq because it allows I2C so the host can write to the I2C register to exit ship mode.  In either mode, applying power to VBUS causes the shipFET to return to IDLE (normal).

    BQ25792 and BQ25798 in QFN package are the same as BQ25790 in WCSP except for no PG, IBAT or BATN pins.  

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Prodigy 10 points

    Many thanks Jeff.

    So the fact that my battery is an array of 9 cells, 3 in series, 3 in parallel, shouldnt still count as 3S?

    If the host is shutdown, will the max charge current revert to 1A when the charger is applied, or can the current be set to 4A as a once-off by the host?

    Can the actual charge current be read back from the I2C registers?

    Does the chip give a % charge figure read back from the I2C registers?

    Best regards

    Martin

  • 0 in reply to Martin Lindsay
    TI__Guru**** 166626 points

    Hi Martin,

    Yes, the 3 parallel is only a concern if the 1C charge current is above the charger capability.  If your application only needs 4A, this family of ICs can provide that.

    Yes and No, if the WD timer is not disabled, the charger reverts to default charge current when the WD timer expires.  So, if the host is up and can disable the WD timer after first power up, the register retain their written values.

    Yes, the IBAT ADC provides the measured instantaneous charge current.

    No, the charger ADC only provides instant measurements of battery voltage and charge current.  A gauge or host software that can read, store and process that data is required for % charge information.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 10 points

    Thanks Jeff,

    My battery has a gauge and Smart Bus, so i guess I could put the battery, host, and BQ2579x on a common I2C bus, which would allow the host to set up the BQ2579x and interrogate the gauge in the battery?

    To set up the BQ2579 would I need to set the max charging current to 4A, and just before host power down disable the watchdog so that the battery can be charged at up to 4A with the host powered down?

    Does T.I. have any devices which use the Smart Bus to talk to a smart battery?

    Best regards

    Martin

  • 0 in reply to Martin Lindsay
    TI__Guru**** 166626 points

    Hi Martin,

    Yes to first 2 questions.

    TI has some SMBus charge controllers with external FETs like BQ25720 but no integrated FET charger like BQ2579x with SMBus.

    Regards,

    Jeff