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Original question:

BQ24074: Charging stopped at 3.8V

BQ24074: Charger does not stop charging when the terminate current is reached

Felipe Schneider
Prodigy 30 points
Part Number: BQ24074

Hello, I am having a big headache with a charger circuit that I have design for my application. The circuit is presented by the circuit below.

The battery is reaching 4.4V and the charging current goes as low as 30mA (or even less) without stopping the charge.

I tried to:

  • Change Rterm to 10k;
  • Remove Rterm.
  • Connect TMR to GND
  • Short the current sensor and the choke to reduce the impedance.

Any advice is much appreciated.

  • 0
    TI__Mastermind 24705 points

    Hi Felipe, 

    Thank you for reaching out via E2E. Please see my comments below. 

    Firstly, I recommend keeping Riterm = 10K and shorting the current sensor and chock for debugging. This allows us to remove the external components as a possible cause of the issue and setting termination threshold higher should make it easier for the device to terminate. For your information expectation is battery will be charged to 4.2V not 4.4V.  

    Can you help to provide a waveform showing BAT pin voltage (not battery terminal) and OUT pin voltage when charge is expected to be terminated? Also if you have the capability to capture the charge current if would be helpful to review how stable the charge current is when battery reaches full charge. 

    Additionally, do you have a load connected at OUT pin and if so what is the current draw? 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 30 points

    Update: I removed everything that was "different" from the recommended design and added the capacitors as recommended. The result: no behave change was observed. The charge was still happening away after it should have stopped and the battery disconnection event was not being detected.

    I then remove the load (there is a 5V boost after the charger) and the battery disconnection event is now being detected and the charge is being ended.

    The problem could be an inductor that I had to change due to low-stock numbers... I just have to fix this in the production batch now...

  • 0
    Prodigy 30 points

    Found the problem and solved:

    The load, which is a boost converter, creates some voltage instabilities at Vout. Those instabilities are probably caused by a high output capacitance at the boost output along with a low current consumption. The result is that the boost turns on and off with a frequency of 55 kHz, making the BQ go crazy, not stopping the charging procedure and not even identifying that the battery was disconnected.

    The solution was to add more 2x 100nF and 2x 10uF capacitors close to the BQ pin 10, which is also close to the boost input.

    Hope it will be of some help to someone else.  

  • 0 in reply to Felipe Schneider
    TI__Mastermind 24705 points

    Hi Felipe, 

    Great to hear you found the problem and thank you for sharing your fix on the forum. 

    Best Regards,

    Garrett