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BQ76925: bq76925 is dead by I2C

Lina Wang
Intellectual 960 points
Part Number: BQ76925

HI  

     my customer usd BQ76925 and one MCU connect with I2C bus, when high frequency to power on and power down, system software will pending on the I2C bus initialize on some time , while reset MCU, system also can't wake up, syetem can work after remove battery pack and then power on,  it seems I2C bus is locked, we want to know why I2C bus will be locked, and how to do unlock? thanks.

in addition when I2C bus is locked, SCL and SDA signal are all high. when I2C bus is locked.

if we have enough time to power on and then power down, there is no this issue. 

  • 0
    TI__Guru 54715 points
    Hi Lina,
    There could be 2 issues. If you put the part to sleep, it will not wake up until the 3.3V discharges. If you are cycling the power quickly the voltage may not be able to fall and the system will look stuck. The other potential issue is that if you are clocking I2C at too high of a frequency the part may be confused and hold the SDA line low locking the bus. When a slave locks the bus in this manner according to the I2C specification the host should send clocks at the proper frequency until the slave releases the bus. It should not take more than 9 clocks.
  • 0 in reply to WM5295
    Intellectual 960 points
    hi WM9295,
    thanks for your reply, I know you pointed two issue, however, I still have some question,
    1. How to know this part is run into sleep mode? because it is power on status, if system is lock stuck for 3.3V discharge enough, whether customer only remove battery to unlock it, is there other way to deal with it?
    2. about your mentioned other potential issue, I don't think so it, because SDA line is high when system lock by I2C.
    3. I see the POR in the spec, but I can't understand clear" VPOR threshold", could you help explain it?
    4.whether this IC lack of reset function, if happen to this issue, whether we can use reset to unlock it.
  • 0 in reply to Lina Wang
    TI__Guru 54715 points
    Hi Lina,
    1, 2. If power is on I2C should work. If the slave is not holding down SDA the host is in control. The host should check the registers to see if the sleep bit is set, if it wants it out of sleep it can set the SLEEP_DIS bit as described in 8.4.1.3 in the bq76925 data sheet. If the part is in sleep allow the 3.3V to fall to complete the sleep operation, then wake it up. The part does not have a reset pin, to reset you would need to remove power. Since there is a 10V abs max limit between VC6 and BAT, you will likely need to remove most cell connections.

    3. See figure 12 of the data sheet
    4. The part does not have a reset pin. See the response to #1.