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bq24297 - how does SYSOVP work exactly?

Nikolaus Schaller
Intellectual 330 points
Other Parts Discussed in Thread: BQ24297, TLV62090

We face a problem that the bq24297 appears to suddenly shut down the path from USB to VSYS for a moment so that the connected Palmas PMIC shuts off.

I have tried everything, incl. setting the ILIM resistor to 0R and programming the ILIM to 0x07 (3A), but we still have these sudden system shutdowns. They do not occur if we supply VSYS from an external buck converter (TLV62090 for ~3.7V).

System current is between 600 mA and 1200 mA, so it remains well below the 3A limit and the voltage at the ILIM pin remains below 1V.

So it is most likely not the IINLIM mechanism.

But I got in one experiment a status register change interrupt from 0x05 to 0x0d (we test without battery and NTC).

I interpret this as SYSOVP but the description in the data sheet is quite short.

From this I could imagine that VSYS did overshoot by some external condition we still have to find, but then it undershoots because the bq24297 turns off the HSFET for a time too long to keep VSYS stable (which has approx. 130 uF decoupling).

So let me ask:

* what is the exact condition to trigger SYSOVP?

* what is meant by converter stops "immediately"? How long does this take?

* is this condition resolved automatically?

* how long does it take to recover?

* can VSYS break down below ca. 3.2V before the regulator restarts?

  • 0
    TI__Expert 8690 points
    Hi Nikolaus,

    SYSOVP triggers when VSYS goes above 200mV of regulation voltage, which in this case of no battery is VSYSOVP ~ VSYSMIN + 150mV + 200mV. Once system voltage goes down to regular voltage regulation of VSYSMIN + 150mV, then converter starts again.

    Status register with 0x0D suggests that input current limit is hit, so VSYS will go down because there is not enough input power to support load power. Make sure you are not loading too much current. This can also occur if VSYS goes below 2.2V, 100mA current limit is active and there is load that prevents VSYS to go above 2.2V.

    Capacitance at the system side may be provoking a big current spike due to inrush current, in which case you may need to implement an inrush current control circuit between our charger and the system.

    Can you use an oscilloscope and probe input current, system voltage and load current? If you don't have a current probe, you can use a 10mohm resistor to sense the currents.

    Thanks,
    Steven