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BQ20Z655-R1: got a VB_T2H_UNKNOWN error. Cannot see flags or connect properly to device. Possible the pack is in SEALED mode.

Rizqi Wahyudin
Prodigy 60 points
Part Number: BQ20Z655-R1

Hi, 

I am trying to troubleshoot my device. The device was initially designed with the gate and source of the DSG and CHG MOSFETs switched around, with wrong footprints also used for zener diodes used for ESD protection on the SMBUS circuit and the PRES (system present) circuit. Upon initial connection with this design, the system worked after removing the SMBUS zener diodes, and I was able to use the BQEASY software to connect successfully to the device. 

However, the device failed after some time, possibly due to the incorrect connections for the DSG and CHG MOSFETs (which were found much later). During this time I got a VB_T2H_NACK error. I have since fixed the connections for the DSG and CHG MOSFETs, and the circuitry of the whole device should now match the one presented in its datasheet. 

Nevertheless, I receive a VB_T2H_UNKNOWN error. I am not sure what this is supposed to mean, given that I did not send any commands or change the device in any manner during the short time which it was functional. Is it possible that this error refers to the device being in a SEALED state, and if so, is it possible to obtain the UnsealKey or any other relevant codes to reverse this? And in addition, is there a set of instructions of how to do this using the BQEASY software? 

Is it also possible that the device is dead? I am not getting any output from the 2.5 V and 3.3 V regulators of the BQ device, so I suppose that is a possibility? Please advise. 

Best regards, 

Rizqi

  • 0
    TI__Guru** 102455 points

    Hello Rizqi,

    It sounds like there has been damage to the gauge, or the gauge is not awake. Make sure to apply voltage on the PACK pin during testing as well. If it is still not communicating then it is most likely damaged if there is no voltage on the regulator outputs.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 60 points

    We have warm-aired our MOSFETs off of our board, checked them for if they are broken, and found that they work just as fine. Still produce a voltage of about 0.4-0.5V between Source and Gate. No short circuits, no sign of deterioriation due to heat or other causes. We soldered them back on, seems like at the output pin of the DSG MOSFET (which leads to PACK), there is a variable and very low voltage of about 54 mV. Do you think it is possible that this is due to a damaged gauge? Is it worth desoldering the gauge and replacing it? Why did the system work when the MOSFETs were connected in the wrong way the first time? 

    Also, there is a low voltage to PACK pin/Source pin of DSG FET, about 250 mV on average. Does this mean that the DSG FET is turned off? If so, why would it be like this from the start, and how would I disable it?  

  • 0 in reply to Wyatt Keller
    Prodigy 60 points

    For future use, is it possible to know the correct method to send commands to SMBUS? I've got this screen on my BQEASY software. I've used 16 (not 17 as seen on the picture) as the target address of my BQ device (as stated in its technical reference manual, and used the following SEND, READ, WRITE fields on the GUI to attempt to use SMBUS commands. 'SMBUS terminated: VB_T2H_UNKNOWN' is always returned when using the programming functions. An example of the inputs I've used is upon writing the UnSealKey (0x60) to the ManufacturerAccess register (0x00): 

    Target address: 0x16
    Write SMB Word :- 
    SMBUS Command: 00, Word(hex): 0060 

    I get the above error message. Same with other uses of the gas gauge's commands. Are there any commands that are more useful to try for testing/our case than others? 



  • 0 in reply to Rizqi Wahyudin
    TI__Guru** 102455 points

    Hello Rizqi,

    Are you still able to get updates on the main registers page or is all communication failing? If it is only on the manual communication tab that you get an error then it is post likely an issue with the sequence you have input manually.

    If you have sealed the device some commands may not be available, make sure the device is unsealed and in firmware mode (ROM mode is address 0x16).

    You can try testing some of the basic read word commands with 0x08 for temperature, 0x09 for voltage, etc.

    Sincerely,

    Wyatt Keller