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BQ25756: 14S2P, 14S3P etc, and alternative power sources

Tracy Hall
Prodigy 10 points
Part Number: BQ25756
Other Parts Discussed in Thread: BQ25750,

Tool/software:

We are in process of design a main "carrier" (NVidia Orin Nano/NX, etc AI Core) system for mobile robotics, Humanoid and otherwise.  The mechanical power come from 14S Lion packs, which due to operating capacity may very likely be parallel chains (about 250Wh per chain, so 14S2P [500Wh] or 14S3P [750Wh} etc).  The "carrier" card is *also* connected to the eBike pack for mobile, untethered operation.

During bring-up and configuration, as well as overnight recovery, it would be useful to allow USB-C power to not only run the main carrier (NOT THE ACTUATORS/MOTORS), but also charge the eBike battery pack.

As such, a few questions:

1) Is either the BQ25756 or BQ25750 appropriate for charging multi-chain (parallel) Battery Packs?

2) Is a protection device (such as the TPS2663x) appropriate to protect the *carrier* (not the actuators/motors) from mis-wired & "hot" connection (for example, when swapping in a charged battery pack)?  Is it compatible with the charging function? (This is necessitated by our target market of University Labs with incoming Grad students of limited practical experience avoiding blowing up expensive equipment).

3) Is the BQ2750 capable of adapting to different power input conditions - such as "slowER" charge from a 60W/100W USB-C and "fastER" charge from a 250W+ DC "wall-wart"?

pushing limits, as always,

Tracy Hall

Chief Dreamer

Dreams and Logic

  • 0
    TI__Mastermind 31275 points

    Hello Tracy,

    1. The battery packs will need to have the same voltage when plugged in the BQ25756/BQ25750. If those battery packs are the same voltage, this will be possible.

    2. I think you'll need a battery monitor to protect the packs. Are you making the packs yourself or are you getting them off the shelf? I can loop in the battery monitor team if you would like.

    3. Yes, this is possible. You'll need an MCU to tell the BQ25756/BQ25750 the correct charging parameters. We have also made an reference design for 100W USB-C charging: https://www.ti.com/tool/PMP41062

    Let me know if you have any other questions.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 10 points

    1. By "same voltage" I have to assume you mean same chemistry/length of chain, NOT the same charge-start (i.e. replace a 14S depleted pack down at 36V with a 14S charged pack at 56V is fine...)

    2. We're hoping for off-the-shelf, but it depends on the not-yet-fully-characterized power profile of the robot/Humanoid in actual use - we would *like* the pack to provide *at least* 1 hour of operation....  In any case, we will purchase a (possibly customized) pack from an existing supplier rather then DIY, so we will specify the monitor needs - I'll pass along a reference to TI...

    3. I'll review the reference design... I don't suppose the Altium Design Files are available?

  • 0 in reply to Tracy Hall
    TI__Mastermind 31275 points

    Hello Tracy,

    1. I think I misunderstand the batteries being charged here. Can you clarify the situation for me? Are you trying to charge multiple battery packs in parallel or you trying to charge different battery packs with different cell counts separately?

    2. Thanks for the clarification here.

    3. I don't have the Altium designs files for that part. I do have the Altium designs files for the BQ25756 EVM though: BQ25756EVM_Design_Files.zip

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 10 points

    1. Well, we have two separate operations going on here:
    1.a. In-circuit charging of a 14SnP pack for off-line (i.e. not moving and/or code development)
    1.b. Multiple 14SnP battery packs - the ones not in-use/in-circuit on independent chargers, then swapped in at-need - since the USB PD will take a fair number of hours to charge a 14S1P pack, let alone 14S2P, 14S3P, etc.  The hope is the USB PD will sustain the system and allow the (externally charged) packs to be swapped in.

    3. Thanks for the files - I've pretty much already implemented from the PDF Schematic & BOM, but extra verification is better.

  • +1 in reply to Tracy Hall
    TI__Mastermind 31275 points

    Hello Tracy,

    Thanks for letting me know about the battery arrangement. The BQ25756 should work for this application. Let me know if you have any other questions.

    Best Regards,
    Ethan Galloway