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Original question:

BQ78350: bq78350 unused LED and other pins HW configuration

BQ78350: Schematic Check of bq78350 Fuel Gauge

Magyar Andras Tamas
Intellectual 400 points
Part Number: BQ78350
Other Parts Discussed in Thread: TIDA-00792, TIDA-010030

Hi experts,

I made a small BMU design for a proto project and I attached its SCH below. Would you be able to check it for me? The design has 13S configuration with separate CHG and DGS path.

Apart from it one question I have: If I want to put a microcontroller into the system and I want that its power consumption to be measured by the gauge the I put its

ground reference after the shunt resistor (from the battery point of view). Can this cause any trouble in the communication since the gauge and AFE ground

is before the shunt resistor? Following common sense, I would say that when the current is high (20-30A) it can cause some 10-15 mV ground reference difference

but apart from it I do not see any issue. Or can I put all ground reference after the shunt so no problem I measure everything and I set Electronics Load register to zero in the bq78350?

3872.Design_to_TI.pdf

Thank for the check/answers in advance, Andras.

  • 0
    TI__Guru* 81034 points

    Hi Andras,

    The schematic attached is for the TI Design TIDA-00792. Are you planning to use the TI Design for your system? If so, you don't need us to review the schematic.

    Your idea to move the ground reference to the other side of the sense resistor does have some disadvantages. The 10mV-15mV reference difference will affect your measurements of the stack voltages and small voltages do make a big difference when it comes to accuracy of the fuel gauge. The safer method would be to use the Electronics Load register.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 400 points

    Hi Matt,

    Actually I modified a lot this reference schematic. One thing I was nut sure is the connections to short for 13S, that’s where I need a confirmation please. So, is that ok like this for 13S?

    Other thing, so If i use other control electronics I simply put ground after the shunt so it will be counted right? And as you said I keep the AFE and gauge before it not to have measurement error..

    Thanks,

    Andras

  • 0 in reply to Magyar Andras Tamas
    TI__Guru* 81034 points

    Hi Andras,

    You can reference TIDA-010030 for a 13S reference design: http://www.ti.com/tool/TIDA-010030 This will show you an example of how to connect the unused cells for 13S.

    I also recommend you follow the reference design for ground placement. It is better to use the Electronics Load parameter than it is to sacrifice gauging accuracy. Your battery voltage measured is going to change with current load which may result in poor gauging and false protection faults.

    Matt