• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 176 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ34Z651: Undocumented state on startup with new device

David Wright33
Intellectual 765 points
Part Number: BQ34Z651

Hi Everyone.

I have just got the first articles of the new revision of my design that uses a BQ34Z651 device to operate battery packs in 2S and 4S configurations (different ROM files).

The previous revision worked just fine in both configurations, and of note to this question, it would startup just fine when the wakeup button was pressed. 

On the new revision however, the 4S configuration starts just fine, but the 2S configuration, when woken with the button enters a state where the FET is under-driven leading to a 3.3V output and very hot DSG FET (VGS =3.3V) when any current is drawn from the battery. Pressing the wake button again, or connecting a charger brings the output up to battery voltage (7.6V when I write this), but any reset of the gas gauge (soft or otherwise) reverts the output back to 3.3V. 

This 3.3V state represents a state where the FET is neigther ON or OFF and is not at all documented and I have never seen before in any previous revision, yet is happening with every first article that I have recieved. The SBS registers display identically with both the 3.3V and 7.6V outputs (DSG being the main bit of note), and the CHG FET enhances just fine with a ~8V VGS as expected. The dataflash ROM is identical between the two revisions despite the differences in behaviour. There are some minor hardware changes from the last revision, but nothing that I can see affecting the gas gauge system. 

I am really struggling to put my finger on what is the issue here, so I would appreciate any input you may have.

For reference the device markings are quite different: new revision =  93AKOPTG4, old revision = 37CG2YTG4

Thanks,

David

  • 0
    TI__Guru** 103125 points

    Hello David,

    Are there any hardware connections/circuit changes from the last revision that could put a load on the gate driver and prevent it from turning the FET on fully? Could you share the schematic, you can also share offline if necessary via private message.

    If the dataflash is the same for both but the new revision is having issues I would really suspect the issue to be hardware as nothing has changed via firmware or data memory. 

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 765 points

    Hi Wyatt, 

    There are a few minor changes to the gate driver circuitry (which you will see in the schematic) to implement a slower rise time on the gate to allow capacitive loads to be charged. But I do not believe these to be an issue for three reasons. 

    1. This circuit was tested by soldering the revevant componets to the previous revision, and this issues did not crop up.
    2. The components for this subcircuit are not actually placed (this is covered in a note on the schematic), so on the PCBs I am testing with, the gate driving circuitry should be functionally identical.
    3. Becasue when the circuit is wake button is pressed (acutally a transistor network you'll see on the schematic) the gate voltage rises to the proper high-side driven value I would expect there not to be an issue with the gas gauge's ability to drive the gate off the bat.

    I am certainly open to you telling me I'm wrong however!

    I have sent you a connection request and will send the schematic to you over a private message when that is accepted. 

    Thanks,

    David

  • 0 in reply to David Wright33
    TI__Guru** 103125 points

    Hello David,

    We can chat offline about this, I think this may be pretty specific for your use case and may not be able to help many others.

    I didn't see your request,  but I sent one to you just now.

    Sincerely,

    Wyatt Keller