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BQ24105: Battery Charger not leaving Precharge Phase

Andrew Kuikman
Prodigy 130 points
Part Number: BQ24105

Hi,

I have designed in the BQ24105 battery charger into our system. The device will charge 3 Lithium Ion batteries in series (750mAh capacity). Since these batteries will be stored long term, and only used for emergencies, the battery vendor has reccomended charging and maintaining them at 12V (as opposed to their max voltage of 12.6V). As such, I have selected 470k and 100k as the feedback resistors to charge to 12V.

I have selected my Riset Resistors to both be 33k, and my Rsns resistor to be 100mOhm. This should give a precharge current of 30mA, and a full charge current of ~300mA. When my batteries are inserted and power applied, the charger shows it is in charging state as expected. When measuring the output current however, it stays at ~30mA, and never increases to the full 300mA charge current.

The current battery voltage is 11.04V, so well beyond the 71.4% threshold for fast charge, yet I never see the charge current increase. I have not left it for more than an hour or two, but I fear under these conditions I will enter timeout and have to power cycle the charger. TTC cap is selected as 100nF.

Any suggestions you can offer would be greatly appreciated.

Thanks,

Andrew

  • 0
    TI__Mastermind 40375 points

    Dear Andrew,

    I am worried that the voltage across the sense resistor is not the recommended value causing issues. In Section 8.3.4, your V_IREG would be the product of the charge current (300 mA) and the RSNS (100 mOhm), or 30 mV. The recommended range is between 100 mV and 200 mV.

    If you want a charge current of 300 mA, I would recommend starting with a V_IREG of 150 mV, giving a sense resistor of 500 mOhm. This makes RISET1 and RISET2 6.66 kOhm.

    Thanks,

    Mike Emanuel

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