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BQ34Z100 minimum current

Buyssens Hubert
Intellectual 685 points
Other Parts Discussed in Thread: BQ34Z100, BQ40Z60

Hello,

I'm designing a product with 1S LiFePO4 battery / 1400mAh.

BQ34Z100 seems to be a good product, because i need to return SOC to the user with LEDs.

But I'm a bit disturbed by the current and the fact that the gauge seems to be always connected to the battery...

My product will have 90% of is life without be used, so if I let my pack connected to the gauge (even in sleep mode=84µA) I will lost about 4.3% capacity per month and about 50% per year. What is quite big... and lose interest of lithium benefit (less self-discharge). Deep sleep is better but still 18% per year.

Is it possible to connect the battery to the BQ34Z100 only when I need it (charging and discharging)?

Is there another way to deal with this problem ?

Regards,

Hubert

  • 0
    TI__Expert 5090 points
    Hi Hubert,

    You can put the device into shutdown by driving the CE pin low when you expect the system to stay idle. Then you can drive the CE pin high to wake the device up, at which point it will calculate SOC based on the voltage at that instant. However, if there is significant current flowing at this time of wakeup, the accuracy of the SOC calculation may not be the best until the part can take a new OCV measurement. You can then leave the device powered during times when you expect to have current flowing (charge or discharge), and it will track those changes and keep the SOC calculation updated.

    Thanks,

    Terry
  • 0 in reply to -Terry
    Intellectual 685 points

    Hi Terry,

    Sounds good. I was using this mode on my last design (BQ40Z60).

    Don't need very good SOC accuracy for my application (need to know if its 0-25% / 25-50% / 50-75% or 75-100%).

    But I don't find any information about it in datasheet (shutdown current,...)?

    Regards,

    Hubert

  • 0 in reply to Buyssens Hubert
    TI__Expert 5090 points
    Hi Hubert,

    The device will consume <1uA when CE is driven low. That powers down all internal circuit blocks, including the internal LDO.

    Thanks,

    Terry
  • 0 in reply to -Terry
    Intellectual 685 points

    good!

    Thanks,

    Hubert