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BQ24070: Charge not terminating.

Paul Slater
Prodigy 150 points
Part Number: BQ24070

Hi,  I have just started testing my boards using the above IC to run a GSM load and in parallel, charge a 10.2Ah li-ion pack to 4.2V.  I am using a 5V wall wart as the PSU.  I tested successfully using the evaluation board, but am having an issue with my own boards.

The load runs fine from the 4.4V output and the STAT pins indicate that the battery pack is charging.  I watched the battery voltage rise to 4.187V, but at that point, it seems to rise no further.  The pack was partially charged when I started and has been on charge for a total of over 11 hours (split over a couple of days), so I would expect termination to have occurred by now.  Interestingly, I placed an ammeter in series with the battery to check if the current had dropped to the 100mA termination level (I am charging at 1A) and after doing this, when I switch the PSU on, termination occurs immediately.  With the ammeter removed from the circuit, the system just sits in fast charge mode.

I have tried a second board and the result is the same.

If I measure the voltage on the ISET1 pin, it reads ~470mV vs a datasheet figure of 230 to 270mV, if this helps.

Is this some sort of impedance issue between the IC and the battery?

Any help greatly appreciated.

  • 0
    TI__Intellectual 1980 points

    Hello,

    Termination will occur when the charge current reach to termination current. and as for the regulation voltage, you should test the voltage of VBAT pin which near to the IC.

  • 0 in reply to Kerry Song
    Prodigy 150 points

    Hi,

    It looks like it was just impatience on my part.  The board finally displayed charge termination after approximately 13 hours.  This was longer than I expected, given that the battery pack was partially charged to begin with.

    What this shows is that if I want to see charge termination and therefore have to have the timer enabled, charging at 1A isn't going to work unless I'm prepared to see timer faults.

    So, I either need to up the charge current or do away with the timer/charge termination altogether.

  • 0 in reply to Paul Slater
    TI__Intellectual 1980 points
    Hello,

    TMR pin could be used to enable/disable safety timer.
    If you want to see termination current, you could use a equipment(like electronic load or source meter), increase the voltage, and see the decrease of current.