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Questions about QUIESCENT CURRENT of BQ24040

Other Parts Discussed in Thread: BQ24040

Hi, Expert,

      I have several questions about the Iq of BQ24040, since we want to design a low power system.

     1. From the spec, Iq is 1uA, when Vin=0V. I am curious are terminals on ISET, ISET2, PRETERM, and TS disabled in this period, even Battery is still on VOUT? 
         From my understanding TS should always be enabled to monitor the temperature of Battery, whatever Vin is ON or OFF. So if it's always on, it will consume ~50uA from Vout, much bigger than the value on spec, am I right?

      2. Iout(done) is 6uA, when VIN=6V, Vout>Vout(reg). I don't understand the condition of Vout>Vout(reg). In what scenario, will Vout>Vout(reg), Vout(reg) is the output setting of internal regulator, which is 4.2V for BQ24040 in typical, Vout is the actual voltage on Vout/Battery. If there's no such scenario, what's the meaning of this parameter?

      3. “The CHG terminal is low (LED on) during the first charge cycle only and turns off once the termination threshold is reached." How could we know the system is still charging, when Vout falls under VRCH, and starts a recharge. Could I get the right CHG status, if I don't re-plug in the adapter to get a new charge cycle?

Thanks so much!

Best regards,

Frank Liu

  • Regarding 1, the TS funtion is used to monitor the battery pack temperature while charging to adjust the internal timer, charge current to follow the JEITA temperature standard. When no input is attached, no charge current is floating into the battery. When VIN is less than UVLO, the part is considered dead and all terminals are high impdance.

    Regarding 2, Iout(done) is the quiescent current at OUT pin when termination is reached. To simulate the termination condition, we increase the voltage on source meter  connecting at OUT pin to higher than VOUT(REG).

    Regarding 3, the /CHG is on during the first charge only (independent of TTDM) and is turned off once battery charge has terminated. This is because of the end user experience. When the end-user plugs in the battery for charging the night before, you do not want them to think it is still charging after a whole night of charge while the battery is only reacharge after charge complete. To reset the /CHG terminal, you will have to cycling input power, pulling the TS terminal low and releasing or entering pre-charge mode.