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BQ20Z45 SCD alarm not clearing with NR set

NR is set

Current Recovery Time is 8s

AFE OC DSG is 0x00 (4.5A in my circuit)

AFE SC DSG Cfg is 0x70 (9.1A in my circuit)

If I set the load for 4.6A, AOCD goes up for 8s, then goes back down.  If the load is still on, the flag goes up again immediately.  This is expected behavior.  If I turn the load off, the flag resets and stays off.

If I set the load to 9.2A, SCD goes up, but after 8s it is still up.  It will not clear itself with the timer.  It should, because NR is set, and  SCD is supposed to behave just like AOCD in that it resets with the timer.

Average current is -3mA. in both cases.

???

  • Not so familar with this aspect but having just checked the TRM the first thing I see is that the clear current  threshold for AOCD and SCD is different,

    For AOCD it is 5mA,

    But for  SCD it is +/-1mA

     

    so I am wondering if current is still -3mA as you indicate whether that prevents it from recovering?

    I also noted in a paragraph above table 2-5 reference to AFC SC Recovery Threshold current but this does not seem to be a parameter you can change on z45

    Digging into it I see that for the z45 AFE SC Recovery threshold seems to be default fixed at 1mA on z45 ( but is hidden so you can't change it) so I think that is where the 1mA in table 2-5 is coming from. If you look at the z65 TRM for example you will see that this paramter is accessible but still also defaults to 1mA.

    e.g I cut this from the z65 TRM

    Hope this is helpfull.

    Mike

     

  • Good call.  there was no reason for a 3mA discharge, so I recalibrated and got it back to 0.  Why it drifted I have no idea.

    Again, SLUA511B leaves some info out about the need for average current being below a preset threshold to recover.  I should have suspected that there would be such a threshold and looked elsewhere for it, but thanks for setting me straight.  I will stick to the TRM from now on.

    Ed K