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BQ24725A: Charger is not communicating over I2C when on battery and without adapter

marko.brelak
Prodigy 90 points
Part Number: BQ24725A
Other Parts Discussed in Thread: BQ28Z610, AM3358

Hi colleagues,

I build a board with the aforementioned IC which on one side has the adapter and on the other two cell battery. The system voltage is powering the Linux based system which is communicating with BQ24725A battery charger and BQ28Z610 fuel gauge over the I2C. 

When the system is on the adapter with the battery attached, I am able to communicate with both the charger and the fuel gauge. But, when I disconnect the adapter at one moment, the system is able to communicate only with the fuel gauge but not with the charger. And they share the same I2C bus. 

I have attached the schematic so if you have any idea for this behavior I would appreciate your suggestion to move forward. 

Thanks in advance

Marko

  • 0
    TI__Mastermind 25800 points

    Hey Marko,

    Can you measure the VCC pin of the charger when you do this test? 

    Can you also measure the +3.3V rail of your system? 

    I want to make sure that the charger is being powered through VCC and also that the I2C bus is pulled up adequately. The second item is less likely as you are able to communicate with the gauge. 

    Secondly, does the gauge have any broadcast feature, allowing it to communicate to the charger?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 90 points

    Hi Joel,

    I have measured the voltage on the VCC pin when it's on the adapter, and the voltage is around 11.3V, then when I remove the adapter it switches to the battery and the VCC is then around 8.2V. 

    I have then measured the 3.3V which is on the I2C bus and it's exactly 3.3V, I am able to communicate with the gauge so the bus is OK. 

    I am not sure about the broadcasting feature of the gauge, at least I have not enabled it explicitly so I don't think that there is any communication going between the charger and the gauge. I was watching the situation on the bus with the logic analyzer and there was no communication unless it's being initiated by the host (am3358).

    Regards,

    Marko

  • 0 in reply to marko.brelak
    TI__Mastermind 25800 points

    Hey Marko,

    I would like you to apply 0.6V to the ACDET pin of the charger while you perform this test. 

    The datasheet specifies that ACDET must be > 0.6V at least, and VCC > UVLO threshold in order for communication to be active. Currently, the VCC requirement is being met. Can you confirm that the ACDET condition is also being met?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 90 points

    Hi Joel,

    I have just performed the test and the procedure was as follows:

    1) Adapter IN, battery ON, ACDET = 2.7V, communication OK

    2) Adapter OUT, battery ON, ACDET = 0V, communication NOK

    Everything is clear now. Before we want to communicate with the charger, we should read the state of the ACOK pin and if the adapter is present then we can start communication. 

    Thank you Joel for your help!

    Regards

    Marko

  • 0 in reply to marko.brelak
    TI__Mastermind 25800 points

    No problem Marko.

    Please submit a new question if anything else comes up. I will close this thread out.

    Regards,

    Joel H