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Original question:

BQ25887: Overcharge and discharge protection?

BQ25887: Discharge protector

JD Peiffer
Prodigy 130 points
Part Number: BQ25887
Other Parts Discussed in Thread: TPS54627, BQ25882, BQ25883, BQ25886

I am considering using the BQ25887 to charge my 2S lipo battery pack.

I would like cell balancing, over voltage and under voltage protection to be incorporated in a PCB we are designing for the project. 

What would be a good under voltage protector for this system? (The Lipo will be connected directly to a voltage regulator, TPS54627, which will power a microcontroller and servos sometimes drawing as much as 2A) Since many battery protectors come with cell balancing, is it necessary that the BQ25887 contains that feature?

JD

  • 0
    TI__Genius 10385 points

    JD,

    The cell balancing system is designed in mind for applications where the end user would be able swap the two cells independently potentially mixing matching the cells. In these situations the battery protector is sometimes include in the individual single cell battery packs rather than on the end equipment and cell balancing would be performed by the charger rather than the protector. With this in mind could you tell me more about your application? There is a whole family of BQ2588X devices and another device may be a better choice.

    As for a battery protector we do not recommend a specific battery protector  for BQ25887, as this is dependent on your battery and overall design. I suggest taking a look through the parametric search on TI.com and finding a few devices compatible with your system and create a new E2E thread asking for a recommendation from battery protector team.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 130 points

    Hi Ricardo,

    My team and I are designing a PCB for a robotic prosthetic hand. We want to be able to plug in a USB and have the PCB charge a LiPo 7.4V 2S, 1300mAh battery pack. We would like the components of the PCB to balance the cells and protect them from over and under voltage. 

    Essentially, we want the cells to be well monitored and stable as they will be in the prosthetic and attached to someone. We do not require any interface with a microcontroller, although this could be nice in the future--same goes for temperature monitoring.

    The battery will output directly to a voltage regulator (TPS54627) as all of our servos and sensors run on 5V. Any suggestions would be helpful, but I will try and look more into options. Just unsure of what to include on which chip, how many we need, etc.


    Thanks,

    JD

  • 0 in reply to JD Peiffer
    TI__Genius 10385 points

    JD,

    Will the individual cells be removable? or is it a single integrated 2S battery pack? If I understand you correctly, you say it is an integrated battery pack. In this case I would let the protection IC handle the cell balancing. 

    The other boost chargers in that family we have are the BQ25882/BQ25883 which are two host controlled devices in different packages and the standalone (no-MCU) BQ25886. An advantage these three alternatives have is that they have power path management. In the event of a damaged or deeply depleted battery the user can still operate the system when connected to USB power. This is accomplished by having a separate pin labelled SYS that maintains a minimum system voltage. You would connect your TPS54627 to the SYS pin and your batteries to the BAT pin.

    Since you are interested in temperature data and other parameters, I would suggest BQ25882/BQ25883 because they have integrated ADCs monitoring various parameters including the battery thermistor reading that can be sent to an MCU over I2C.

    Thanks,

    RIcardo