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BQ24040: Part going into thermal shut down with higher capacity battery packs

Tim Christensen
Prodigy 90 points
Part Number: BQ24040
Other Parts Discussed in Thread: BQ24090, BQ24072

I have been using both BQ24040 and BQ24090 parts for charging Li-ion pack < 2500mA without issue at 750mA.   I have new pack at 3200mA-H and now BQ's are going into thermal shutdown.  I have determined it is due to the new packs have a lower initial voltage and now the BQ linear regulator is overheating from the extra input to output voltage drop.    Obviously I can reduce fast current limit to reduce power but this will also reduce charge time on these higher capacity batteries.     My question to TI support,    if these BQ parts go into thermal shutdown until the batteries attain a 3.8V level,   will this degrade or harm the chip?

  • 0
    TI__Genius 13700 points
    Hello Timothy,

    Please see the response that I made to your other post on a variation of this same issue here:

    e2e.ti.com/.../2089897

    That said I want to take some time to talk about the situation that you are experiencing.

    What does your layout look like for the bq24040 or bq24090? Depending on what your layout looks like you may be experiencing this thermal limiting because the heat generated by the charger does not have sufficient means of moving away from the part and dissipating causing the die temperature to increase to the point of thermal regulation.

    Ways that you can try to address this is the through the use of vias in the thermal pad that are attached to a large GND pour on an internal or bottom layer. Also if you look at Figure 39 of hte bq24040 datasheet you can also remove the thermal relief traces going to the thermal pad and replace them with larger copper pours to spread the heat away form the device more effectively.

    Another option would be to explore a part such as the bq24072 which is a similar linear charger but it is in a slightly larger IC package with a larger thermal pad. These two features will dramatically help the thermal regulation of the charger possibly helping it to avoid the thermal regulation state that you have been seeing with your larger capacity battery.

    Finally another solution would be to explore using a switch mode charge to improve your charging efficiency and access even higher charge rates to improve your charge times with these larger new batteries.

    I am interested in hearing your thoughts.