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BQ40Z50: Low Side FET Configuration Possible?

Joseph DeWitt
Intellectual 320 points
Part Number: BQ40Z50
Other Parts Discussed in Thread: BQ76920, BQ78350

Hi,

Is it possible to convert the BQ40Z50 IC into a low side FET through the CHG and DSG circuit configuration illustrated in the attached schematic which I obtained from the BQ76920 IC?

Alternatively, does Texas Instrument have a low side FET fuel gauge IC for 3 cells in series which is comprised of a single IC as opposed to requiring two as is the case with the BQ76920 and BQ78350 configuration?

Best regards,

Joe DeWitt

  • 0
    TI__Guru** 105870 points

    Hello Joe,

    Both the monitors and gauges have similar AFEs, so I believe this configuration may work. I am concerned about the Vgs of the DSG FET since we use the PACK and BAT voltages as a reference for the charge pumps, so when the gauge turns the FETs on it will be the 3S stack voltage plus 10v-15v from the charge pumps. but let me check with the monitor team since I am not familiar with this work around. 

    Sincerely,

    Wyatt Keller

  • +1 in reply to Wyatt Keller
    TI__Guru** 105870 points

    Hello Joe,

    I talked with the monitor team, the low side protections should work with the gauge the same as the monitor, you can follow this app note for more explanations: https://www.ti.com/lit/sluaa84a

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 320 points

    Hi Wyatt,

    That is incredible news! Thanks so much for the support. This guidance really helps me move forward with my application design. I really appreciate it. 

    Best regards,


    Joe 

  • 0 in reply to Wyatt Keller
    Intellectual 320 points

    Hi Wyatt,

    One quick follow up question. I reviewed the information in the link you provided for the BQ769X2 battery monitors and it looks like to convert these IC's from high side to low side the digital output DCHG and DDSG pins need to be used. The BQ40Z50 IC's do not have these digital output pins. Is this to say that in order for a high side FET IC to be capable of being converted into a low side FET, the IC needs to contain digital DCHG and DDSG pins and therefore the BQ40Z50 can't undergo this change?

    Or am I misunderstanding something and the BQ40Z50's can in fact be converted into low side FET operation?

    Best regards,

    Joe DeWitt

  • +1 in reply to Joseph DeWitt
    TI__Guru** 105870 points

    Hello Joe,

    You can use a lot of the same logic in the application note and use the high side drivers on the gauge, you may need to level shift for this though. Otherwise I would recommend checking the GPIO functionality of the gauge, you can set the LED pins as GPIOs that can be controlled by different flags in the gauge, so you can link two pins with the DSG and CHG bits for example.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 320 points

    Hi Wyatt,


    Wow, I had no idea that was even possible. Very cool feedback. Okay sounds great, looks like I have some more information to digest and some additional design work to do but as always, thanks for guidance and insight. I really appreciate it.

    Best regards,

    Joe DeWitt