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BQ76940: device x-ready

Arash Iranfar
Prodigy 70 points
Part Number: BQ76940

Hi, 

I've been trying to design a BMS board using BQ76940 for a while now! Since I am new to designing power electronic boards, so I don't have that much confidence in my design to connect the board directly to a Li-Ion battery pack. I made a resistor array of 75Ohm resistors and somewhat made a model of a 48V battery pack. I am not drawing any current from the board and the charge/discharge FETs are not soldered to the board yet just to make sure if something goes wrong there is no unfixable damage done to the board.

I am using an STM32F407 microcontroller and I translated the SparkFun library for BQ769x0 which is originally coded for Arduino into an ARM-compatible library. I don't think that there is a problem with this part. The actual issue is the "Device X-ready" fault that the microcontroller is not able to clear. I searched the questions asked about this problem and still, I couldn't make the board work:

1- The cap1, cap2, cap3 voltages are almost equal to 3.3.

2- The BAT+ to VC10X = VC10X to VC5X = VC5X to BAT- = 16.

3- I changed the BQ chip just in case but the newly soldered chip didn't work too. 

4- I don't think that there is a problem with the connection of the simulated battery pack to the board.

5- The TS1, TS2, TS3 are connected to their respected references (GND, VC5X, VC10X).

What else can cause the problem? Does the fact that I'm using the resistor array instead of a real battery pack has anything to do with the problem? Are the charge/discharge FETs a necessary addition to the board in order to avoid the "Device X-ready" fault?

Any clues can be helpful because I am really out of ideas now and I don't know what else can be done. I attached the board design and codes in the following in case you would want to check them.

Thanks for your concern, 

Arash.

8233.BQ76940.rar

P.S. 1: When I plug the board to the power supply the chip doesn't automatically start working and I have to boot it manually with the onboard pushbutton, but after that, it starts communicating with the microcontroller just fine.

P.S. 2: Sorry I didn't know how else should I attached the files... 

  • 0
    TI__Genius 10830 points

    Hi Arash,
    Thank you for your interest in BQ76940. Our team is out of the office for the week-end but will reply quickly after they return.


  • 0
    TI__Guru* 81034 points

    Hi Arash,

    The XREADY fault is caused by one of the upper cell groups (6-10 or 11-15) not getting the proper voltages.

    When you connect your resistor divider, have you connected to each cell input and measured the voltage at each of the pins (VC0-VC15)?

    Do you have a thermistor or 10k resistor connected to each of the TS pins?

    Check the voltage on REGOUT. Also for CAP1, CAP2, CAP3, you say they are 3.3V - is this relative to GND, VC5X, and VC10X?

    Have you tried to clear the XReady fault by writing a '1' to this bit? It is possible that the fault occurred during power-up and needs to be cleared.

    What is connected on the other side of R81? It has a blank label on the connector. This should be connected to PACK+

    Best regards,

    Matt