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BQ51050B: Won't charge below 3.0V

Ian Mellor
Prodigy 40 points
Part Number: BQ51050B
Other Parts Discussed in Thread: BQ51003, BQ51013B-Q1, BQ51013B

Hi, we are using a BQ51050B for Qi charging. The problem is that the BQ51050 won't charge the battery if its voltage is below 3V.

This can happen if the battery drains after a long period of non use and the PCM (2.7V) switches off, however this problem also happens with the PCM removed. 

Our battery is 100mAh which we would like to charge a 1C.

According to the data sheet if the battery is below Vlowv (approx. 3.0V) it should enter PRECHG mode but it doesn't under any circumstances.

We've tried with different Chargers and Qi antennas, our current charger uses a Renesas P9235A. With the Renesas part we can see normal operation and communications between the devices.

Also, the circuit should have a charge current limit of 100mA with R36 at 2K94 and R40 at 200R but it is about 50mA? If we use a 1K52 for R36 we do get a 100mA charge. This indicates Kilim is well outside spec!?

We have tried removing our attempted fix of D1/R33.

The schematic is attached.

Do you have any idea what could be going wrong?

Thanks Ian

  • 0
    TI__Guru 68936 points

    Hi Ian

    The BQ5105XB is designed for higher charge currents and we do not recommend charging below 500mA.  Problem is the accuracy of current measured by the ILIM pin which is a sample of the output current.  The accuracy of sample decreases with current below 500mA. 

    For lower currents we have a reference design, see TIDA-00318

    Ian Mellor said:
    The problem is that the BQ51050 won't charge the battery if its voltage is below 3V.

    Can you send a scope capture of the start up?  

    We should see the OUT pin go up in voltage to try and reset the protection circuit.

  • 0 in reply to Bill Johns
    Prodigy 40 points

    Hi Bill,

    Scoping this is very difficult as we are testing with real batteries and just testing in the two states (battery > 3.0V and < 3.0V).

    So attached are links to two videos show our test setup and tests in both of these states.

    During the tests the PCM is shorted out, so it does not disconnect.

    The problem with the BQ51003 is it's micro BGA footprint which means we have to use HDI PCBs which is costly and limits our suppliers.

    Do you have any other devices you can suggest? 

    Since the IC is not designed recommended for operating at such a low charge current is it possible the IC is not able to go into such a low, low current mode?

    Do you have a Eval PCB to test this?

    Please let me know what you think.

    Thanks

    Ian

    Download Attachment

    Available until 20 Aug 2023

     

     

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  • 0 in reply to Bill Johns
    Prodigy 40 points

    Hi Bill,

    Another question.....could I swap out the BQ51050 with the BQ51013B-Q1 (seems only a slight difference on Pin 10)?

    And would it help?

    BTW if you need me to scope let me know how to set it up and I'll try.

    Thanks

    Ian

  • 0 in reply to Ian Mellor
    TI__Guru 68936 points

    Hi Ian

    Yes the BQ51013B / 013-Q1 will fit a BQ51050 footprint.  Note that your are changing from a battery charger to 5V power supply.

    Pin 10 changes from TERM to EN1 (OK to GND).

    You would want to increase current limit not what it is a power supply.