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BQ24316: Undervoltage Lock Out Threshold Seems Too Low?

James Olson
Prodigy 200 points
Part Number: BQ24316
Other Parts Discussed in Thread: BQ24090

Attached to this posting is snippet from the BQ24316 data sheet pertaining to the undervoltage lock-out feature for the IN pin.

If lithium ion cell voltages are generally north of 3V and as high as 4.3V at end of charge, why is the designed-in UVLO level so low?

It seems to me that the UVLO threshold should have been, say, 4.7V to account for the highest possible cell voltage plus the voltage drop through the gating FET inside the BQ24316.

Because the IN pin serves a dual purpose (the input to UVLO/OVP functionality and the upstream side of the gating FET) it's not possible to externally force the UVLO threshold higher with a resistor divider.  Plus any tinkering with the UVLO threshold would also move the OVP level higher, too.

  • 0
    Prodigy 200 points

    I didn't see an opportunity to edit my question, so I'll simply respond to it.

    My goal is to make a single cell lithium ion charger powered from a USB C power source.  There are numerous instances where the USB C power source's voltage could be too low to serve as a 500mA battery charger.  Examples are: overburdened USB port on the laptop, low quality or excessively low USB cable.

    Do I need to construct a true UVLO detector externally that pulls BQ24316's CE pin low when the IN pin voltage is above 4.7V?

    As the BQ24316 is designed it seems UVLO detection really means "the minimum voltage at which I'll wake up, not sufficient voltage to power the BQ24090 attached to me".



  • +1 in reply to James Olson
    TI__Expert 8526 points

    Hi James, 

    Yes, you are correct with your understanding that UVLO is the, "UVLO detection really means "the minimum voltage at which I'll wake up."  It is the threshold for the device to power back on and reset.

    The BQ24316 is designed as an overvoltage and overcurrent protector--not undervoltage.  This is why UVLO is not designed to be used as an undervoltage threshold to toggle FETs or trigger protection signals.  It is designed to keep the device powered down in the case of very low battery voltage.

    If you are interested in a UVLO that has a higher threshold, then I recommend implementing your own protection circuitry outside the BQ24316.

    Best,

    Andria