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[FAQ] TITLE – BQ24040 and BQ2404X family Vin to Vout vs Charge Current Regulation.

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When the battery voltage is low, between 3V and 3.6V the charge current is normal, 800mA. But as battery voltage increase the charge current begins to drop from 800mA  to 460mA, battery is well below 4.2V for the start of constant voltage.

What could be causing this problem?

Best Regards,

Bill Johns,  Applications Engineer

Texas Instruments Inc

Dallas, Texas

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  • This also applies to BQ21040, BQ24050 and BQ24090 family of devices.

    The BQ2404X and similar devices are linear chargers comparable to a low drop out regulator, for correct operation they will require some voltage drop input to output.

    Specification in the date sheet for Vin – Vout Drop-Out is 325mV typical and 500mV max. But note that the test condition is R-ISET = 540, this is 1A output current and I-out reduced to 0.5A. This would be a reduction in output current from 1A to 500mA. Charging in this condition continues and will complete without problem.
    This behavior is most common with larger charge currents, 1A when the device and near Constant Voltage phase where the input to output voltage difference is lowest.
    To prevent current from reducing during charge voltage across the device should be in the 700mV to 1V range.

    The device also has IN-DPM feature that will also reduce output current when input voltage drops. But IN-DPM is active when input voltage drops to 4.4V.

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas

    Please click "This resolved my issue" button if this post answers your question.

    For more information on Battery Charger Solutions see Link

    Tip -- Improve search results by including "FAQ" 

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