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Bq24105 issue Battery conn/disconn

Franco Marcotulli
Prodigy 220 points
Other Parts Discussed in Thread: BQ24105

Hi,

I'm using Bq24105 to charge 3 cells, in general without problems.

On my circuit I can plug the Battery pack and the DC plug (power supply -15V).

So

1) if I plug first the battery pack and then the power supply, I haven't issues.

2) If I plug the power supply, so that the IC is on, and then I plug the battery pack, the IC charges at costant current the pack, but without termination

and without a decreasing of current.

So, when the IC is ON is possibile to insert/de-insert a battery pack, or this lead to a permanet issue on the IC?

  • 0
    TI__Mastermind 31120 points

    The IC is hard wired to have the CC/CV program algorithm (see Block Diagram in the data sheet).

    The CC and CV loops are "OR" together and reduce the duty cycle (reduces power delivered) if either the current or voltage get to the set threshold.

    The only reason that the voltage would not regulate and stay in CC mode is if the feedback voltage was below the feedback voltage regulation threshold of 2.1V.  Please check that.

    If the input and battery were plugged in pretty much at the same time and the battery was over 4.1V per cell, then possible the algorithm might think the battery is full and terminated and does not charge until the voltage drops below the 4.1V threshold, which is not a safety issue or an operation issue since the battery is basically determined full and the system can still run off the of "full" battery.

    If you are over charging your cell...not going into voltage regulation and tapering at the correct voltage, then something is wrong with the feedback going to the IC.

    This IC has sold in the millions and we would have seen any over charge conditions.  Let us know what you find.

  • 0 in reply to Charles Mauney
    Prodigy 220 points

    Thx for your reply but I replaced the IC before you answered me.

    I'm goign to plug and unplug the battery and DC power supply to re-create the issue. After I'll verify the feedback voltage regulation threshold of 2.1V like you suggested me.

    By the way, I'm modifying my circuit so that if I've the DC plug inserted (IC on), I've the CE pin tied to VCC by a resistor and when I connect the battery pack the pin goes to ground enabling the charging. I think this is a little improvement and a right way to manage this circuit.

  • 0 in reply to Franco Marcotulli
    Prodigy 220 points

    I wrote on my file limit for RSET1 (5k-10k) and RSET2 (1,2K-10k)

    but I don't remeber where I read them. Furthermore, is it possibile increase RSET2 to decrease the ITERM under 15mA?

    It's the MIN on the datasheet but It seems possibile in my test. 

    Thx in advance.

  • 0 in reply to Franco Marcotulli
    TI__Mastermind 31120 points

    Not sure what you mean about writting the file limit.  The Charge and termination are set by resistors and the votlage across the resistor should be proportional to current.

    You can set the termination current level lower, but if you get too low the accuarcy of the circuit might push the lower limit to below zero and then the charge would not terminate.

    Not terminating is not an issue since the battery will not charge once it fully charges to the regulation voltage (ie. current tapers to zero).