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bq24170 Charge Termination

Charles Gervasi
Expert 2270 points
Other Parts Discussed in Thread: BQ24170

Everything about bq24170 is working for us except charge termination.  We are using three cells.  We see it do the 2A constant current mode.  When it hits 12.6V, voltage stays constant and current drops normally.  The trouble is it never terminates and never asserts the STAT pin. 


We have TTC disabled by pulling the pin to VREF.  This should disable timeout but enable termination when current falls to 10% of constant-current charge current.  Instead charging never terminates and current slowly dwindles as the battery tops off.  What are we missing?


Thanks!


CJ

  • 0 in reply to Charles Gervasi
    TI__Expert 3160 points

    Charles,

    Do you have a capture of this behavior? How low can you measure the charge current going? Based on your description of the set-up I agree it should be terminating at 10% of the current set on the ISET pin (200mA) +/- 25%. What is STAT showing?

    Just to be clear, in your post you say you're pulling TTC to VREF which would disable the safety timer but would allow termination, but in your schematic you have a cap on TTC which should allow termination and safety timer. 

     

    Thanks!

    Rachel 

  • 0 in reply to Rachel Moore
    Expert 2270 points

    Thanks for ressponding to my question.

    Rachel Moore said:

    How low can you measure the charge current going?

    We measure it going down to 20mA.  We can see if it goes even lower.

    Rachel Moore said:
    Based on your description of the set-up I agree it should be terminating at 10% of the current set on the ISET pin (200mA) +/- 25%. What is STAT showing? 

    STAT line is not asserting.  It shows charging not complete.  

    Rachel Moore said:
    Just to be clear, in your post you say you're pulling TTC to VREF which would disable the safety timer but would allow termination, but in your schematic you have a cap on TTC which should allow termination and safety timer.

    We have removed the cap and run a wire to VREF.  We've looked at that pin on the scope and it appears to have a clean 3.3V signal.

     

    Thanks!

    Rachel 

  • 0 in reply to Charles Gervasi
    Expert 2270 points
    My colleague says it's now working. I saw it exhibiting the behavior yesterday. He says he changed the value the LED's current limiting resistor, and it started working.

    He mentioned seeing it working right on a Fluke. When I saw the problem, I was using a cheap Sinometer. Maybe the voltage drop across the current meter was an issue.

    I'm going to check it again next time I'm in the office.
  • 0 in reply to Charles Gervasi
    Expert 2270 points
    I checked it again. It's working perfectly. I'm not sure what we were doing wrong Monday. Thanks for your help.
  • 0 in reply to Charles Gervasi
    TI__Expert 3160 points
    Glad everything is working for you now!