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Original question:

BQ24090: bq24090 safety timer didn't end

BQ24090: How to check the safety timer

user4498844
Prodigy 165 points
Part Number: BQ24090

Hi!


I would like to check if the safety timer on the BQ24090 is working fine.

In the test the cell is charged and discharged at the same time (i try to keep cell voltage on 3.3V). I detected that charging did not stop after 10 hours (cell volatge was 3,3V and charging current was 600mA).

Could you explain why it happend? Why charging proces is not stopped?

Best regrads!

  • 0
    TI__Mastermind 22240 points

    Hi,

    Do you have a schematic you can share? If the device is in TTDM "Charge" mode (TS pin is pulled high or floating), then the timer function is disabled. Another possibility is that the timer was reset due to UVLO, TS or /BAT_EN disabling, a short at the output, or falling below V_LOWV.

    Can you explain how you are charging and discharging at the same time while maintaining the 3.3V?

  • 0 in reply to Anthony P Pham
    Prodigy 165 points

    In the attachment I am sending a fragment of my scheme.

    In addition in our solution we use a SN2040, but it is the same as a BQ24090.

  • 0 in reply to user4498844
    TI__Mastermind 22240 points

    Hi,

    Just a few questions to understand what's going on:

    • How are you charging and discharging to keep the device at 3.3V? I'd like to understand your test setup to understand how the device is behaving.

    • What is the votlage seen at the TS pin when the CHG_ON/OFF is high and low? Are you able to provide a votlage waveform of the toggle?
    • What is the voltage at the /CHG pin when you expect the timer to expire? If the timer expires, it is expected to be high impedance.
    • What current are you seeing going into the battery when you expect the timer to expire?

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    Hello,
    Thank you for your support.

    Anthony P Pham said:
    How are you charging and discharging to keep the device at 3.3V? I'd like to understand your test setup to understand how the device is behaving.

    This is our test setup

    Anthony P Pham said:
    What is the votlage seen at the TS pin when the CHG_ON/OFF is high and low? Are you able to provide a votlage waveform of the toggle?

    This is the waveform of the TS pin when toggle on.

    Anthony P Pham said:
    What current are you seeing going into the battery when you expect the timer to expire

    For 22.5 hours the current is fairly constant (influenced by IC temperature throttling), after 22.5 hours it suddenly drops to 5 mA.

  • 0 in reply to Andrzej Szykowny
    TI__Mastermind 22240 points

    Hi

    Andrzej Szykowny said:

    For 22.5 hours the current is fairly constant (influenced by IC temperature throttling), after 22.5 hours it suddenly drops to 5 mA.

    You mention IC temperature throttling. If the IC enters thermal regulation, slows the timer clock by half and reduces the charge current. What you are seeing is within the range of normal operation based on the min and max values of the charge safety timer value.