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BQ24078: Safety time fail

GaryC
Intellectual 2775 points
Part Number: BQ24078

We design the safety time out is around 9hr. but the result is over 10hr. May I know how to correct the safety timer. Thx

Rtmr=68k, 9hr

BR, Gary

Schematic:

  • 0
    TI__Mastermind 22440 points

    Hi Gary, 

    Please see my comments below.

    Rtmr = 68kohms is correct to set safety timer to typically value of 9 hrs. Rtmr = 68kohms sets typical safety timer to 9.07 hrs to be precise.

    Although please keep in mind there is a specification on the accuracy of the timer. Some part to part variation is possible. On the BQ24078 datasheet page 8 Ktmr has a min value of 36 and a max value of 60. 

    Using max Ktmr of 60 for the calculation safety timer with Rtmr = 68kohms can be as long as approx. 11.33 hrs. 

    Therefore the reported safety timer of over 10 hours is not out of specification according to the datasheet. 

    Best Regards,

    Garrett