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BQ24035: Upper operating range stability concerns

Abel Elbaile28
Prodigy 70 points
Part Number: BQ24035
Other Parts Discussed in Thread: BQ24160

Hi everyone,

Reading the datasheet for the BQ24035 (Specifically the  bq24032ARHLR) and it's 4.4V regulated voltage output when plugged into an AC adapter one question arises;

  • Q1 is acting as a regulator (Vac >=4.4v)
  • My system is drawing 750mA (Ilimit for AC) for batt charging and around 1.1A* are drawn to power up the system.

Here it goes: What happens if AC supply voltage is on the upper limit ~15V and my system is drawing the 1.85A through the poor Q1 regulating that vast voltage difference? Should special thermal considerations be taken into account? Is it pushing the part too far?

*The actual load is around 600mA, however, due to cellular radio bursts, the averaged current can go up to (and in certain cases surpass) 1.1A

Also, there's a figure I can't find when the DPPM hooks up the system load directly to the battery, what's the maximum current that can flow from the battery to the load?

Thanks,

  • 0
    TI__Guru 69076 points
    Hello
    The device has thermal regulation for batt charging, when the die temp reaches about 125C charge current is reduced. If the die temp rises further the unit will shutdown, 155C.
    Current between battery and out (Supplement Mode) is not limited see page 10 note 19.
  • 0 in reply to Bill Johns
    Prodigy 70 points

    Hi Bill, thanks for your reply.

    Despite the thermal regulation for batt charging, powering the load through the IC when it's plugged to an AC-DC adapter at the upper side of the operating range ~15V and a 1.85A load won't be an issue?

    Thanks,

  • 0 in reply to Abel Elbaile28
    TI__Guru 69076 points
    Yes if the load / charge current remains high and AC input voltage is in 15V range power dissipation on the device will be high. This device does not shutdown at higher input voltage like our newer generation of devices such as bq2407X. BQ24035 does shutdown at 6.6V.
    Additional thermal plane on the device will help along with reducing voltage at AC input, better adapter or power resistor to drop some of the voltage.
    If the AC input is expected to be high then reducing it using a buck converter would help. Also a switching charger similar to bq24160 may be and option (max AC input may be a little low).