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BQ24251: I2C hanging when both USB and battery connected

Part Number: BQ24251

Hi team

I have used this part in a previous design with no problems but in standalone mode.  With a new modification I have sorted everything out with pin reassignment using the USB to power the circuit with no problem.  The last part is to connect our usual battery and that is where the fun has started!  The I2C comms now fails if I connect both the battery and the USB supply.  As far as I can tell, the BQ24251 (BQ) is hanging at random times with the data line still low.  This causes a bus collision condition for the PIC which then cannot send a Stop command.  Resetting the PIC’s I2C does not fix it because it is a BQ problem.  Only removing the power clears it.  Have you come across this at all?  I have 2 PCBs and both do the same.

  • Hey ajayt,

    We have not encountered this issue before on this part.

    Is this a custom designed board, or are you using our EVM?

    You mentioned it hangs up when both the Battery and VIN are applied? What the communication speed? To what rail are you pulling up the I2C line? 


    Joel H