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BQ78350-R1: BQ78350-R1 in SMBUS drive mode

Nicolas OTAL
Prodigy 70 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: EV2400, BQ78350, BQ76920, BQ76930, BQ76940

Hello everyone, I'm new on the forum ! I'm starting with TI components. For a small battery voltage level reading project I want to use the BQ78350-R1 component that would come directly to read a SMBUS, from a battery, is it possible to simply connect it to the SMBUS and drive the LEDs for voltage levels defined like that? And use SCA/SCL for programming it with EV2400 ?

  • 0
    TI__Guru* 79583 points

    Hi Nicolas,

    I'm afraid it is much more complicated than that. The BQ78350 is a battery gauge that does much more than translate voltage levels to determine the state of charge. It uses a complex algorithm to determine the state of charge based on voltage of the battery cells, temperature of the cells and current flow through a sense resistor and it tracks the charge accumulated over time. It must be used with a companion battery monitor (BQ76920, BQ76930, or BQ76940) as it is not a stand-alone device. The SCL and SDA pins are used to communicate with the companion battery monitor. I recommend taking a look at the document Using the BQ78350-R1: https://www.ti.com/lit/pdf/slua924 

    Setting up a battery gauge for a specific battery takes a significant amount of effort since the battery discharge curve needs to be captured over different current loads and temperatures to determine the gauging coefficients. 

    For your project, you may be better off using an ADC and MCU together. It will not be near as accurate (battery gauging is a complex art), but if your goal is to light five LEDs, it may be the most efficient solution.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 70 points

    Hello Matt !

    Thank you for your response. After I think maybe I misspoke. I just want to recover data from the SMBus already present on a BMS.Use directly the information from the battery to SMBD and SMBCLK of the BQ78350 to read the voltage of my BMS. My BMS is already sending information in SMBus and I just want to interpret it with the BQ78350 which would drive LEDs.

  • 0 in reply to Nicolas OTAL
    TI__Guru* 79583 points

    Hi Nicolas,

    I'm not sure I fully understand. The BQ78350 SMBus is used to configure the BQ78350 data flash registers and to read various parameters like cell voltages, current, temperature, SOC, protection status, etc. The BQ78350 can only work with a companion battery monitor (BQ76920/930/940) and gets all of its measurements from the battery monitor (using the I2C bus). It cannot function without the companion device. (The companion device even provides the power to the BQ78350). The BQ78350 will light the LEDs based on what it has calculated for the SOC of the device - this is a very complex algorithm to determine the SOC and it is dependent on all of the measurement data from the battery monitor. 

    I think you want the BQ78350 to read the SOC from the BMS and light the correct number of LEDs? Unfortunately, this is not possible. Let me know if I am not understanding correctly.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 70 points

    Ah yes it's clearer on my side! I hadn't realized that the BQ78350 can only work with a companion battery monitor (BQ76920/930/940). I thought I could directly program the BQ78350 to drive the LEDs. Thank you very much Matt for your help. I'm going to look at a solution using an ADC and MCU together.