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BQ2000T: no new charge cycle when threshold VRCH=1,9V is reached

M. Jaeckle
Prodigy 95 points
Other Parts Discussed in Thread: BQ2000T

Initial Situation:
- We use the Texas Instruments-IC:   BQ2000T
- We load a accumulator and when the  threshold  VMCV = 2.0V is reached at the BAT-Pin (PIN 4)  the voltage-regulation starts
- And the accu will load full
=> So long is all OK

No the Problem:
- The Accumulator is a built in accu
- The accu is full and he has a self discharging (a few days)
- The voltage at the BAT-PIN drops from VMCV = 2,0V down
- When the threshold VRCH = 1,9V  is reached  (at the BAT-PIN),  the IC should start a new charge-cycle
- And this new charge cycle do not happens

Questions:
- What is the problem, that don´t happen a new charge cycle ?

 

Best regards,
Markus

  • TI__Guru**** 150690 points

    You should be able to open your own post and click 'edit' at the bottom left.  This should allow you to change the post title.

    If I understand correctly, you are charging a lithium battery pack.  It should terminate CC charge and move to CV charge when the BAT pin voltage reaches 2V.

    It should also begin a new charge cycle when the BAT pin drops below 1.9V.  This and the 2V have a tolerance associated with them.  How are you measuring the BAT pin voltage?  If you decrease the battery voltage a little more, to around 1.8V, does it start charging?

    Do you also need to charge a nickel pack with this same charger?  We have other, newer ICs that are better suited for nickel charging.

  • in reply to Chris Glaser
    Prodigy 95 points

    I have found the "edit-Button", thank you.

     

    To the Problem:
    - 1.: fast charge (constant current-Mode, the LED is on)
    - 2.: the voltage rise at the BAT-PIN  (while current Mode)
    - 3.: when the BAT-Pin reaches VMCV=2,0V  the constant curent Mode  will terminated (LED goes off)                           =>  this is correct, and does work
    - 4.: now the Battery pack has a self discharge and goes in a few days to the threshold VRCH=1,9V  at the BAT-PIN
    - 5.: but there is now reloading now

     

    - I measuring the BAT-PIN with a scope
    - I have decrease the battery-voltage at the BAT-PIN  (with a potentiometer) to 1,0V but there happens no reloading

  • in reply to M. Jaeckle
    TI__Guru**** 150690 points

    The LED should not turn off because you are still in fast charge--CV not CC, though.  If the LED turns off, then the charger thinks you have a nickel chemistry.  In nickel chemistry charging, you end up in the trickle maintenance state, not the done state (unless the 2V MCV is reached).  When the LED turns off, do you still see the MOD pin pulsing?

    Are you using a thermistor?  If so, replace it with a resistor instead to rule out any dT/dt termination.  The other way to get out of fast charge is for the timer to expire.  Can you confirm it is set long enough to charge your lithium cell?

    Can you post a schematic?