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BQ78350+BQ76940+MCU programming

Armin
Intellectual 290 points
Other Parts Discussed in Thread: BQ76940, BQ78350, EV2400

Hello everybody,


I plan to design a pcb with BMS and some other functions. I want to combine the BQ78350, the BQ76940 and an MCU (Atmel ATmega with Two Wire Interface) on this board for that task. The Atmel-Controller shall comunicate via SMBus with the BQ78350 to get some data about battery status for further functions of the board.

I am not clear about programming the BQ78350 and BQ76940 on my board. Can I do this with the Battery Management Studio or the BQ769X0 Evaluation Software from TI and the EV2400 via the BQ78350-SMBus? 

Do I have to open the SMBus-connection between Atmel-controller and BQ78350 for programming?

While programming the BQ78350 and BQ76940 is is it neccesary to connect the battery pack to my board or do I just need the voltage of the EV2400?


Thanks a lot


Armin

  • 0
    Mastermind 8415 points

    Hi Armin,

    Do you mean programming the firmware into the BQ78350, or just configuring the parameters?

    The firmware of the BQ78350 can be programmed with the EV2300 (we had problems with the EV2400 when the ICs were first released but I believe this problem has been resolved). So unless someone says otherwise, you can probably use the EV2400 as well.

    To configuring the BQ78350, there are 2 ways: BQ Studio or using the Data Flash Access command (You'll find all the information in the Reference Manual of the BQ78350).

    For production, the second method will probably be better. The Data Flash Access command would be between your Atmel microcontroller and the BQ78350. On your atmel, you could do a bridge from a UART to I2C (SMBus) peripheral to transfer the settings to the BQ78350.

    For design purposes, use BQ Studio with the EV module. I also recommend that you look at the layout provided by TI in the EVM user guide to see how to switch the SMBus between a PC and your microcontroller to communicate with the BQ78350.

    For the power, you do need to have an external power connected to the battery side since the BQ76940 needs to be powered to communicate with the BQ78350 (on the EVM, the BQ76940 has an LDO to power the BQ78350). From what I recall, you only need about 5V for the BQ76940 LDO to work. Even though the EV2400 provides a voltage pin, the pin on the connector of the EVM is not mapped.

    I hope this helps

  • 0 in reply to Michel Solecki
    Intellectual 290 points

    Hi Michel,

    thanks a lot for this fast and good answer. It really helps me!

    Both firmware flashing and configuring bq78350 and bq 76940 are interesting for my application.

    I have some other questions to you:

    -For configuring I have to power the 76940 at BAT and VSS pin and also REGSRC to power the 78350 right? So that means that the SMBus of 78350 works with 2.5V. But the EV2400 is working with 3.3V on SMBus. I read I have to disconnect the on board pull-ups on my pcb for programming with the EV2400 since it has its own pull-ups. Okay.  But is it possible to work with different voltages on the bus? If yes then I think I need a common ground of EV2400 and bq78350 isnt it?

    -Can I configure the bq76940 through the bq78350. I dont have to connect the bq76940 directly to the EV2400?

    Thanks a lot

    Armin

  • 0 in reply to Michel Solecki
    Intellectual 290 points
    Hi Michel,


    thanks alot for this fast and good answer. It really helps me!

    Both firmware flashing and configuring bq78350 and bq 76940 are interesting for my application.

    I have some other questions to you:

    -For configuring I have to power the 76940 at BAT and VSS pin and also REGSRC to power the 78350 right? So that means that the SMBus of 78350 works with 2.5V. But the EV2400 is working with 3.3V on SMBus. I read I have to disconnect the on board pull-ups on my pcb for programming with the EV2400 since it has its own pull-ups. Okay. But is it possible to work with different voltages on the bus? If yes then I think I need a common ground of EV2400 and bq78350 isnt it?

    -Can I configure the bq76940 through the bq78350. I dont have to connect the bq76940 directly to the EV2400?


    Thanks a lot

    Armin
  • 0 in reply to Armin
    Mastermind 8415 points

    Yes, you do need to connect BAT+ and REGSRC to your power and VSS to ground. I recommend to look at the schematics (in the EVM user guide) once again for a good example on how to do this (especially for the REGSRC pin).

    For SMBus, there are  pull-ups on the line and therefore, the device that wants to communicate only needs to pull and release the data and clock pins low. So the BQ78350 needs to be able to tolerate the operating voltage of your microcontroller (check the specs of the BQ78350 to make sure that it does; we have our microcontroller running at 3.3V). And yes, both EV module and BQ78350 need to have a common ground since each device needs to pull the lines low to communicate.

    Lastly, no you don't need to connect the BQ76940 to the EV module. Everything is handled by the BQ78350 through the I2C bus.

    Michel

  • 0 in reply to Michel Solecki
    Intellectual 290 points

    Hi Michel,


    okay. Thanks a lot for helping my a lot!!!

    I will do so.

    Armin