• State
  • Locked Locked
  • Replies 9 replies
  • Subscribers 64 subscribers
  • Views 455 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76930: BQ76930

shaoze Xu
Prodigy 10 points
Part Number: BQ76930

Problem：

中文：应用BQ76930作为前端来采集电芯电压，板上电芯连接如下：

VC0 - VC1----Cell1

VC1 - VC2----Cell2

VC2 - VC4----Cell3

VC4 - VC5----Cell4

VC5B - VC6----Cell5

VC6 - VC7----Cell6

VC7 - VC9----Cell7

VC9 - VC10----Cell8

发现一部分电池包存在上位机读取的电芯数值与实际用高精度万用表测量数值差异较大的情况，如图所示

从表中可以看出Cell1-Cell4万用表测量值和上位机读取值相近，但Cell5-Cell8两个种方式的测量值差异较大，超出了我们的规格，请问是什么原因导致这种差异？

 

English：Apply BQ76930 to measure the voltage of the battery cell, and connect the battery cells on the board as follows:

VC0 - VC1----Cell1

VC1 - VC2----Cell2

VC2 - VC4----Cell3

VC4 - VC5----Cell4

VC5B - VC6----Cell5

VC6 - VC7----Cell6

VC7 - VC9----Cell7

VC9 - VC10----Cell8

we found that some battery packs had significant differences between the cell values read by the upper computer and the values measured with a high-precision multimeter, as above in the figure.

From the figure, it can be seen that the measurement values of the Cell1-Cell4 multimeter are similar to those read by the upper computer, but the difference between the measurement values of the Cell5-Cell8 multimeter and those of the upper computer is significant, exceeding our specifications. What is the reason for this difference?

Sincerely,

shaoze.Xu

  • 0
    TI__Mastermind 34710 points

    Hello Shaoze,

    Can you share your system's schematics?

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hello Luis,

    Related part of system's schematics as below

     

    Best Regards,

    shaoze.Xu

  • 0 in reply to shaoze Xu
    TI__Mastermind 34710 points

    Hello Shaoze,

    Could you share the whole schematic for the AFE?

    By the way, what is the Zener value? Have you tried placing the IC on an EVM to see if the error is still there?

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hello Luis,

    The whole schematic for the AFE as below

    and the Zener value as below

    Unfortunately, i do not have an EVM to test it, later, I will replace the IC with a large voltage difference to other pack with a small voltage difference to observe if this phenomenon still exists.

    Best Regards,

    Shaoze.Xu

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hello Luis,

    Can i solve this problem by software verification？

    Best Regards,

    Shaoze.Xu

  • 0 in reply to shaoze Xu
    TI__Mastermind 34710 points

    Hello Shaoze,

    Looking at the schematic, the only thing I notice missing is a 1-kOhm resistor from Cell 4 to VC4x. See the following image for an example:

    This is an excerpt from the TIDA-01093 reference design. I do not see the 1-kOhm as shown in the reference design, you could try placing one like this and see if there's a change.

    Now, if the error is just an offset of around the same mV in your boards, you can probably correct this in the software by applying an offset.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hello Luis,

    I apply a verification method as below，

    take Cell1 as example, calculate the slope by a cell reference voltage ，such as 3.3V，the slope is get from  dividing the actual value by the value from computer，then i can calculate this cell at the other voltages, value from computer multiply by the slope, after that, i will get the verified value.The formula is as follows：

    Slope = （Actual value * 10000）/ Value from computer

    Verified value = (Value from computer * Slope) / 10000

    I can use above formula to calculate verification value of the entire voltage section of Cell 1，

    the other Cell will use the same mothod as above.

    If my method is feasible？

    Best Regards,

    Shaoze.Xu

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hello Luis，

    can you understand my verification method and if  it is feasible, I hope to receive your reply as soon as possible.

    Best Regards,

    Shaoze.Xu

  • 0 in reply to shaoze Xu
    TI__Mastermind 34710 points

    Hello Shaoze,

    I would imagine that you would need to calculate an offset. To calculate an offset you would need to take the voltage at two known voltage references. Then calculate the slope and see what is the offset.

    This is assuming that the error in cell 8 is due an offset error.

    Best Regards,

    Luis Hernandez Salomon