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BQ24002: Does the bq24002 charge 18650 lithium-ion batteries?

William McKinney
Prodigy 210 points
Part Number: BQ24002
Other Parts Discussed in Thread: BQ24040, BQ25170

I realize the bq24002 is obsolete, but it happened to make it into one of our product designs.  I also have an obsolete BQ24002RGWEVM board.   Neither our board, nor the out-of-the-box evaluation board appears to be capable of charging depleted 18650 batteries.   When the EVM board is enabled it immediately signals that the battery is 90% charged.   It looks like the 18650 batteries immediately jump to a voltage greater that 4V when charging is enabled.  I have several different makes of 18650 lithium-ion batteries and they all behave the same way -- none of them charge when using the BQ24002RGWEVM, the bq24002 immediately signals that all the batteries are 90% charged.  I have never seen the bq24002 in a constant current mode above the trickle charge current.  Is there something about the bq24002 that isn't compatible with 18650 batteries, and can you recommend a different part for charging a pair of 18650 batteries?

Thank you,

--Bill

  • 0
    TI__Guru 69176 points

    Hi Bill

    The BQ24002 should charge an 18650.

    Do you have a schematic of the circuit you can share?

    Any info on the battery would help, p/n, capacity?

    On a discharged battery the protectory should open when voltage gets too low (3V to 2V) to prevent excessive discharge.  When charger is turned on it will supply 60mA and that should be enough to reset the protector and start charge.  Sounds like something is going wrong during this step.

  • 0 in reply to Bill Johns
    Prodigy 210 points

    I'm seeing this behavior in the BQ2400xRGWEVM, which is why I find this so confusing.   No mods to the board.  The positive terminal of the battery is connected to BAT+ and SENSE+, the negative terminal to DC- on J7.  A 5V bench supply is connected to J1.  Defaults for all the other jumpers.  Current limiting on the supply is completely off.  The EVM will briefly (less than a second) a red LED for ST1 and then will immeditately shift to a green LED for ST2 with the ST1 LED off.  

    The 18650s I have are made by Ultralife, CBJJ, Liion Wholesale, and EBL.  

    I guess since the bq24002 is obsolete that this is probably moot.   Can you recommend another part + eval board for the next spin of the product?   I'd like to avoid an I2C interface to the part if possible and control it like the bq24002.

    Thank you.

  • 0 in reply to William McKinney
    TI__Guru 69176 points

    Hi Bill

    Yes the BQ24002 is an older device and we have several newer better devices.  A couple of devices to look at BQ25170 and BQ24040.

  • 0 in reply to Bill Johns
    Prodigy 210 points

    Actually, neither of those parts delivers the 1A charge current that the bq24002 claims to deliver.   I'll look around.   But it would be really interesting to know why an out-of-the-box bq24002 evm doesn't work with any 18650 battery that I have.

  • 0 in reply to William McKinney
    TI__Guru 69176 points

    Hi Bill

    Ran more test on the BQ24002 and cannot see the issue that is causing problem.  

    What voltage are you seeing on the the battery when this happens?

  • 0 in reply to Bill Johns
    Prodigy 210 points

    Thank you for looking at this, I apologize for taking so long to reply.  Here's a scope shot of what happens when I apply 5V to the DC+- inputs of the eval board:

    The purple line is the 5V input, cyan is the battery voltage and the green and pink are ST1 and ST2 at the diode cathodes, respectively.

    I have a current meter on the battery line and see the trickle charge current, about 65mA on the meter.   This current never changes, and an hour later the meter still shows about 65mA with the ST1 LED lit and the ST2 LED off.   I have yet to see the bq24002 on any board charge an 18650 at anything but the trickle charge current.   I have no idea what I might be doing to cause this.   Since the bq24002 is an obsolete part and we need to re-spin our board anyway, I'm going to chalk this up to unknown and make sure I see expected charge curves using an eval board on the new version.    Thank you again for your time.