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BQ24725A: Oscillating Input Current issue

Jeevan M
Prodigy 100 points
Part Number: BQ24725A


Hello,

Battery Charger IC part number = BQ24725A

Data sheet Link : https://www.ti.com/lit/ds/symlink/bq24725a.pdf?ts=1642661417693

 

We are setting two current values in the charge current register (0x14h) as per the datasheet in our target device.

 

In our Target device after we wait for 10-15minutes and power cycle the device then the input current oscillates between 0.7A and 1.2A.

 

We have observed this issue a couple of times. When the Target device/unit is turned on, the battery charging current normally is a constant current. 

 

Occasionally the unit drops into an abnormal state with battery charging current pulsing, 0.01A current and 0.8A current with 1 second pulse width and 50% duty cycle. This profile appears to be due to the charging controller mistakenly charging the battery as if the unit were turned OFF.

 

Reproducing the Issue.

Start with a running unit which has a 

  • partially charge battery installed and 
  • connected to the DC supply and 
  • does not exhibit the oscillating current behavior.

To reproduce the issue, we simply remove and re-insert the battery. The unit will start to exhibit the oscillating current issue. So kindly help us with any register level setting or any configuration need to be done to resolve the oscillating current issue.

 

Regards,

Jeevan M

  • 0
    TI__Genius 10240 points

    Hi Jeevan,

    Could you please make some clarifications about the values of two current level setting in the REG0x14 and the reason for waiting 10-15 minutes? If the charge current has two levels, then the input current would have two different levels.

    Could you provide the waveforms of the PHASE, input current and the the charging current when the oscillation happens?

    Best regards,

    Eric

  • 0 in reply to ezhao
    Prodigy 100 points

    To meet our requirements, we have set the charging current for 2560 mA (register value = 0x0A00) when the device is in OFF condition and 896 mA (register value = 0x0380) when the device is in ON condition. The reason for waiting approx10 min is because at that time interval every time, it is showing oscillation in the current reading.

  • 0 in reply to Jeevan M
    TI__Mastermind 41935 points

    Dear Jeevan,

    Can you please capture some waveforms of the input current, PHASE, SRN, and charging current when the oscillation happens?

    What is the system load that is being used? The input current will change as the load current changes, which is comprised of the system current and the charge current.

    What happens if you try to disable charge using the Charge Inhibit bit?

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 100 points

    The following is the input current waveform when the device is in ON state

    Input current waveform

    We are setting the Charge Options Register (0x12H) in the following way and it will disable battery charging if we set the last bit to 1 according to the data sheet.

    #define CONFIG_CHARGER_CHARGE_DISABLE        0xB903U /*!< Disable battery charging*/
    #define CONFIG_CHARGER_CHARGE_ENABLE         0xB902U /*!< Enable battery charging*/

    Below is the spike (3A) we are getting when the device is in ON state for every 50 seconds.

    Current spike

  • 0 in reply to Jeevan M
    TI__Mastermind 41935 points

    Dear Jeevan,

    Can you please send a schematic? I need to check this before moving forward.

    Thanks,

    Mike Emanuel

  • 0 in reply to Jeevan M
    TI__Mastermind 41935 points

    Dear Jeevan,

    Please send the waveform of the PHASE node when the issue is happening. It would be helpful if you could capture the input current, PHASE, SRN, and charging current at the same time; I see you have a four channel oscilloscope. Please take a waveform demonstrating the switching period, and then a waveform zoomed out a bit.

    Thanks,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 100 points

    Dear Michael,

    There is shortage of current probe here and as the issue is related to input current we have measured the input current. I am posting more clear image of the waveform below.

    Input current spike

    Here we can observe that battery is removed at the beginning with an input current of around 750 mA. Then the battery is inserted now and now the input current is around 1.5 A. 

    Now after 50 seconds we can see the 3 A spike coming. This is repeating at every 50 second interval.

  • 0 in reply to Jeevan M
    TI__Mastermind 41935 points

    Dear Jeevan,

    Can you please provide more information about the system load and the charging current at each instance shown above? This "spike" is happening for about 1 second. We need to understand more about how the current is being transferred to the load(s). The current in general seems consistent, we just need to figure out what happens during that 1 second interval. Knowing the battery voltage and how the PHASE voltage is behaving will better assist with the debug.

    Thanks,

    Mike Emanuel