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BMS: solution or ref design proposal

Alen Barisic
Intellectual 1300 points
Other Parts Discussed in Thread: BQ25155, BQ25505

Hello,

one of my customers is starting a BMS project where they need some advice.

- Li-Ion Cells (one or more in paralel, only one in series - 3.7V)

- The lion cell has no protection circuitry. Is a protection circuit needed when the battery is permanently installed?

- charging takes place through a small solar cell (additionally via USB)

- low power consumption

- precise detection of battery fuel status, best case with additional consideration of self-discharge, aging

- small Layout and cheap

Which components would you recommend to cover the main functions? Which optional components would you suggest?

Thanks,

Alen

  • 0
    TI__Intellectual 1300 points

    - charging current through USB 500mA,  through solar cell much less

    - discharge current max 10mA, transient peaks ~1A

  • 0 in reply to Alen Barisic
    TI__Guru**** 166916 points

    Hi Alen,

    TI does not have a single IC that provides battery pack protection, gauging functionality and charging.  It is highly recommended for all batteries to have pack protector in order to prevent overvoltage and, more importantly, overcurrent and undervoltage.  Charger's typically have redundant overvoltage protection to prevent over-charging.  Chargers with NVDC powerpath also have a last resort (typically high current and very slow responding) overdischarge protection and (<=2.5V) undervoltage protection.  

    That said, my recommendation is the BQ25155 linear charger with integrated ADC.  The host software can use the ADC to measure instantaneous voltages and currents.  While these measurements alone are not enough information to compute battery capacity, like a battery gauge can, host software and memory could compute battery capacity from these measurements.  If the solar panel MPP is 4.2V-4.9V and has ISC > a 10 mA or so, then the host could also use the BQ25155's VINDPM feature to prevent the charger from collapsing the high impedance solar panel source while charging.

    If the solar panel voltage MPP is < 4.2V, then I recommend adding a boost charger like BQ25505, with VBAT_SEC output connected in parallel to the BQ25155 BAT output.

    Regards,

    Jeff