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BQ24450: Operating temperature range

William Ham
Intellectual 260 points
Other Parts Discussed in Thread: BQ24450, BQ24650

The BQ24450 data sheet states that the recommended Tj(max) is 70C while the absolute max is 150C.  Figure 3 (graph) shows the linearity of the internal reference (Vref) within the recommended Tj limits.  Is there any characterization of the component outside of this band, say to 85C?


Thanks in advance.


  • 0
    TI__Guru**** 151520 points

    I'm sorry but there is no data available above that temperature range.  This is usually not an issue for our battery chargers as the batteries themselves, in many cases, cannot be exposed to such high or low temperatures.

  • 0 in reply to Chris Glaser
    TI__Guru 71526 points

    If we extend the graph another 20C, and draw the line for VRef, would this be a close approximation?  It is rather disconcerting to say the device will operate up to 150C, but then only provide data to 70C without any supporting data.  I'm guessing there must be some characterization data somewhere, yes?

    Also, the battery may be remote from the actual charger, so the temperatures may be different, correct?

     

  • 0 in reply to LeonardEllis
    TI__Guru**** 151520 points

    The abs max ratings come from the silicon process used to make the IC.  Certain processes can break at certain temperatures.  Breaking is a permanent failure, not just being a little out of spec.  As the note under the abs max table says,

    "These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is not implied."

    The device has been characterized over the recommended operating conditions range.  There is no data that I know of outside of this range.  You should operate our devices within their recommended operating conditions.

    If the batteries are at a significantly different temperature than the charger, then the temperature compensating reference voltage would make the charging operation non-ideal.

    The bq24650 is characterized over a wider junction temperature range and can charge lead acid cells.

  • 0 in reply to Chris Glaser
    Intellectual 260 points

    Thank you for the quick reply!

    I knew it was a "shot in the dark."

    I was not only interested in operating characteristics but also interested if there were any potential hazards introduced at the slightly elevated temperature.  Since that information looks to be unavailable, would you have any guidance for independent extended temperature tests? (i.e. specific issues/operation that might warrant special attention)  Shutdown, UV, UI and charge voltage out of tolerance (+/-10) is not a problem.

    Thanks again!

    Bill

  • 0 in reply to William Ham
    TI__Guru**** 151520 points

    The variation of the internal reference voltage would be the biggest thing to check but if you're not concerned with your charging voltage then it shouldn't matter for you.  Other items to check, which might vary over temperature, would be the current sense circuitry and the gate driver for the pass transistor.  Making sure it can source/sink the needed current at the needed voltage.

  • 0 in reply to Chris Glaser
    Intellectual 260 points

    Thank you all for the answers/feedback!  

    I will look into the BQ24650 as an alternate.  The test recommendations are valuable and I will keep them in mind for any BQ24450 testing that occurs.

    Thanks again!

    Bill