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BQ25672: different chemistry charging vs LTC

Charles Jenkins59
Intellectual 360 points
Part Number: BQ25672
Other Parts Discussed in Thread: DRV8847, BQ24650, BQ25798

We designed in the LTC4162-SAD in a remote monitoring application as it was dedicated to lead acid which is needed for temp performance. We later found the bq25672.  The TI part appears to do what the LTC will not do and that is regulate the load side of the charger to less than 18V so as to protect our TI DRV8847 motor driver which has a max voltage of 18V.  The LTC part's power path is passed straight through to the load which could be close to 24V in a solar charger application.  If I read the TI data sheet correctly the TI part would buck down the solar open circuit voltage to a setpoint less than 18V.  This also protects our application if there is a battery failure in that the solar input could then power the load with a regulated voltage.

Second issue is chemistry.  The bq25672/692 claim to be LiPO, LiFePO4 chargers. Can they be programmed to charge a 12V 1.3Ahr AGM battery?

And are these assumptions about the TI part correct?

Thank you for your help

Charlie Jenkins
Former Ti FAE.

  • 0
    TI__Guru*** 143880 points

    Hi Charles,

    The BQ25672 uses NVDC power path which means that the SYS load plus charge current is provided by the output of the dc/dc converter.  The SYS output OVP voltage, where the converter stops switching, is 110% typical of BATREG.  The min voltage is set in a register called SYSMIN.

    Regarding the different chemistry, the charger uses an asynchronous state machine to provide a Lithium battery charge profile.  That state machine relies on I2C registers to make decisions.  You could write host software to change the profile from CC-CV-termination to CC-CV-float-CV-float-etc, similar to what was done with additional external circuitry for the standalone BQ24650, which passes input to SYS output, in the appnote below.  We provide a generic driver to help make simple I2C reads and writes but not the lead acid profile.

    One more thing, the BQ25672 is a spin of BQ2579x family.  One of the members of that family is the BQ25798.  The 798 uses the family's VINDPM feature to implement MPP by periodically stopping the converter, sampling the input VOC and resetting VINDPM to the user programmed percentage of VOC.  IF you want a more accurate MPP point then you could set manually with fixed VINDPM, then you might consider 798 instead.

    Regards,

    Jeff