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BQ24040: Termination and Safety Timer Questions

Allan Fan
Expert 7090 points
Part Number: BQ24040
Other Parts Discussed in Thread: BQ24075

Tool/software:

Hi expert,

May I clarify with you some questions regarding BQ24040?

1. since there is no BATFET between BAT and SYS, how can battery be charged to full (stop charging) and still providing source to SYS?

2. if it would be hard to terminate, it will trip 10hr safety timer. But once it tripped the timer, SYS would drop as well, right? Could you please explain more the description " A system load can be placed in parallel with the battery as long as the average system load does not keep the battery from charging fully during the 10 hour safety timer." in the DS?

Thanks,

Allan

  • 0
    TI__Mastermind 40435 points

    Hi Allan,

    Which part are you asking about? BQ24040 or BQ27404?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Expert 7090 points

    sorry for the typo, it's BQ24040

  • 0 in reply to Allan Fan
    TI__Mastermind 40435 points

    Hello,

    The customer has to implement their own power path as we do not provide one. If the System is powered directly from BAT, its load will affect the charging state of the battery.

    As shown in Section 8.4.10, "If either the 30 minute or ten hour timer times out, the charging is terminated and the CHG terminal goes high impedance if not already in that state. The timer is reset by disabling the IC, cycling power or going into and out of TTDM."

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 10 points

    Hi, Mike, Allan:

        Thanks for you both for the support!

        I am Peter Tao, who is the customer delivering this question to Allan originally. Could I make a summary as below after referring to your comments.

    1. Power path solution(like BQ24075 or external own power path) is suggested for a big load current scenario, example in my application, load current might be 0~220mA, depending different user setting, not fixed.

    2. BQ24040 might still work for a small load current scenario,  for example if load current is less than 50mA. Proper PreTerm setting(For example set term 100mA, pre-charge 200mA) could still have chance to make the charging system work well and safe.

       Please correct me if any mistake or confusion.

  • 0 in reply to Xi Tao
    TI__Expert 7090 points

    Hi Peter,

    Yes, your understanding is correct.

    1. for larger load current, smaller Ichg may trip 10hr safety timer.

    2. for smaller load current, larger Ichg could have chance to terminate within safety timer. 

    Regards,

    Allan

  • 0 in reply to Allan Fan
    TI__Expert 8325 points

    Hello,

    Let me know if there are any other questions and I'd be happy to help.

    Best regards,

    Alec