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BQ21040: Need a better definition for Constant Current / Constant Voltage

David Nelson2
Prodigy 20 points
Part Number: BQ21040

Need to understand at what voltage does the BQ21040 start to reduce the current?  I was expecting it to be around 4.2V but it actually starts dropping at 3.8V.  I'm not using the temperature sense and I am trying to charge a 3.7V Li Ion battery at 1C=169mA.  Thanks.

  • 0
    TI__Mastermind 19195 points

    Hi David,

    Current reduction of a few mA would be normal at 3.8V, how much are you seeing on this unit? 

    The regulation voltage for BQ21040 is given in the datasheet (min/typical/max) : 

    Best,

  • 0 in reply to Nick Brylski
    Prodigy 20 points

    Hi Nick,  Thanks for the quick response.  the current starts to drop once the voltage reaches 3.8V.  It decrease at a fairly linear rate down to about 30uA.  the chrg pin goes low when the voltage gets to 4.1V which is around 30mA.  The current continues to decrease to the 30uA range and the voltage continues to climb to ~4.17V.  Is this expected behavior?

    Thanks,
    David

  • 0 in reply to David Nelson2
    TI__Mastermind 19195 points

    Hi David,

    1. The charging current at 4.1V should be close to the fast charge value, if you are seeing 30mA when setting it 169mA something else may be going on here
    2. /CHG should be low during charging, and high impedance when charging is complete or not charging

    What is the input voltage level?

    Please upload the schematic here. 

    Best,