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BQ78350-R1: BQStudio doesn't recognise the device

Christodoulos Protopapas
Prodigy 100 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQSTUDIO, EV2400, BQ76930, , BQ78350

Hello again,

I am becoming a regular on these forums but I need your assistance once again.

We have designed our own PCB which uses the BQ7630 and the BQ78350DBT-R1.  We have followed the reference designs in SLVU925C and we are designing for 8S.  We are using the EV2400 to communicate between the device and BQStudio.  Currently for testing, we have connected each cell input in series with 150 ohm resistors and apply 26V from BATT+/PACK+ to BATT- so as to get 3.25V across each "cell".  Measuring each individual cell inputs we get the correct voltage.

We have also shorted PRESS and BOOT to ground using jumper wires.  Measuring REGOUT while BOOT is grounded shows that there is not REGOUT.  We connect the EV2400 to SMBC, SMBD and GND.  Then we momentarily connect BOOT to C1 at 3.25V and ground it again.  Measuring REGOUT it is at 2.5V as expected.

However opening BQStudio next, the device is not recognised.  Nonetheless we choose 1E9B_1_03-bq78350_R1.bqz.  We tried Unsealing the device and updating the firmware, however it says there is no acknowledgement from the device.  We thought it might be a communication issue but we checked the I2C pins between the two and they are at 2.4V.  Also checked SMBC and SMBD and they are at 3.13V.

EDIT:  We have been running tests until now with now results. We noticed that CAP1-VSS is 4.5V instead of max 3.6V which raises some suspicions

Any ideas are appreciated thanks,

Chris

  • 0
    TI__Guru 54715 points

    Hi Chris,

    4.5V on CAP1 would seem to indicate a damaged BQ76930.  From your description I don't see what would have happened   You mention unsealing which would seem to indicate you talked to the part at some point to seal it. A new part or one just programmed will just talk without needing to unseal.

    The information from the BQ76930 is critical to the BQ78350-R1 gauge.  If it can't find the gauge it will ignore the SMB lines trying to talk to the BQ769x0.  You might put a scope on the SCL, SDA to see if they are toggling continuously indicating the gauge is trying to talk to the BQ76930.  If there is 4.5V on CAP1 the BQ76930 may be dead and  unable to respond. 

  • 0 in reply to WM5295
    Prodigy 100 points

    Hello,

    Thank you very much for your reply. We changed the BQ76930 and removed the BJT which was connecting to CAP1 at the base (which controls the LEDs).  Now the voltage at CAP1 is 3.3V as expected.  However, bqStudio still doesn't recognise our device. 

    We have also probed the SDA, SCL, ALERT and VEN and the signals look as expected which I assume means that there is communication between BQ78350 an BQ76930.  Probing at the SMBUS, the voltage if fixed high though.  We tested the EV2400 with the development board and it could recognise that device. Here are the scope images:

    SDA and SCL

    VEN and ALERT

    We have also grounded the SMBA which should be the default address.  I can't pinpoint what the problem is..

    EDIT:  We ended up changing the BQ78350-R1 as well an now it gets recognised!  It is strange though as the CAP1 shouldn't affect the gauge.  In any case, I do believe that current flowed through the base of that BJT and fried both ICs.

    Thank you,

    Chris

  • 0 in reply to Christodoulos Protopapas
    TI__Guru 54715 points

    Hi Chris,

    Thanks for the update.  Thinking about it there was a post on e2e a few years ago where the NPN had overheated causing high voltage to the CAP1 and damaging the BQ769x0.  I think the BQ78350-R1 would also be damaged since the LED pin voltages would also go up even if REGOUT from the BQ769x0 to VCC was still normal. 

    If you have a 3 or 3.3V supply for LEDs, that is a great alternative to the NPN.

    Anyway glad you have it working!