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BQ76920EVM: Device gets recognised initially but not after a few seconds

Part Number: BQ76920EVM
Other Parts Discussed in Thread: BQSTUDIO, , BQ76930, EV2400, BQ76920, BQ78350, BQ78350-R1

Hello,

I am using the EV2400 with the BQ76920EVM and running the bqStudio.  My plan was to set any parameters I could now, while waiting for our custom board to be delivered, which will use BQ76930. 

However I have now ran into a problem where, following the datasheet I connect 15V, connect through SMBUS and press the Boot button, bqStudio recognises the device for a few seconds but then it goes back to not recognising it.  Everything was working normally until I set the cell count to 8.  I believe this was the error, as the BQ76920 only supports up to 6 cells.  Unfortunately I don't see a way to set it back to 5 cells, as in order to do that I have to reconnect through bqStudio.

If that is not the problem, I don't understand what the problem could be as it was working fine prior to making that change.  Any ideas what it could be?

Thank you,

Chris

  • Hi Chris,

    I think the cell count is the issue - I assume you are setting this on the BQ78350 device. When a very low voltage is detected on one of the cells, a voltage-based Shutdown will be triggered and the default delay is a few seconds. You will either need to quickly update this value before the Shutdown is triggered (press the boot button and quickly write the correct value to this register), or you may need to rewrite the firmware to the device if the first option does not work. The firmware can be downloaded from the BQ78350-R1 product folder on ti.com.

    Best regards,

    Matt

  • Hello,

    Thanks for the reply, I believed that would be the issue.

    I firstly tried changing the AFE cell map value to 1F as soon as the device is recognised, but, even though the visual cell colours change, it doesn't seem to register and it goes off again.

    I then tried updating the firmware, but it was telling me I need to be in ROM mode.  So I searched how to enter ROM mode and found I need to send 0F00.  I used the Advanced comm SMB and put Command 00, write word 0F00 and got a success (the technical reference manual is not very clear regarding the address of the register I am accessing, unless I missed it?)  Nevertheless, I got a success on the transaction log with 0F00.  I went back to the Firmware tab, but it still told me I need to be in ROM mode.  Autoscan was turned off as well, as I saw a post where it said it needed to be off.  All these were done quickly, while the device was still recognised.

    I am not too sure how to continue from here, my only lead is that I am trying to access ROM mode wrongly.

    Thanks, 

    Chris

  • Hi Chris,

    Just before you click on the button to write the Firmware, try pressing the Boot button on the EVM. When the firmware is programmed, BQStudio will automatically try to put the device into ROM mode, so you do not need to send the command separately. 

    I think the trick is trying to either write the AFE cell map or start the Firmware programming immediately after the device wakes up before it goes back into Shutdown.

    Matt

  • Hello,

    Thank you very much for your response.  I have tried it again however with no positive results.

    When pressing the firmware Program button as soon as I press the Boot button, either it tells me that I need to be in ROM mode or it is giving me a "An internal error occurred during: Dashboard" and the error being java.lang.NullPointerException.

    If those are the only two solutions then I guess we can try soldering a new component on the board.

    Thanks,

    Chris

    EDIT: We changed the BQ78350-R1 and everything is working fine now.  Thank you for the ideas anyway!

  • Glad to hear you had a new device handy and everything is working!

    Best regards,

    Matt