BQ27426: Question about RA update rule discharge current?

hello，

Background of the question:

Since the discharge current requirement of Bq27426 is >C/10, but the discharge current in our application does not always satisfy >C/10, and the average current does not satisfy >C/10, we would like to make the discharge current >C/10 at the moment of current collection; and keep the original discharge current (maybe <C/10) at the moment of non-collection.

Question:

1. When the discharge current > Dsg Current Threshold and 500 seconds after the start of the discharge, start the 30 seconds timer?

Dominik Hartl11 said:

#2: The gauge must be in discharge state. See the TRM for state transition info. It also must be outside the transient zone (wait for 500s, defaul setting). 

2, Is there a register that can be used for judgment when starting a 30 second timer?
3, If the current > C/10 also crosses 1 RA grid point, but the discharge time is < 500 seconds, is Ra updated? What value is used for the current value at this point?
4. If the current > C/10 also crosses 1 Ra grid point, but the discharge duration is only 529 seconds, is Ra updated? What value is used for the current value at this point?
5. If the current > C/10 also crosses 1 Ra grid point, but the discharge duration is < 30 seconds, is Ra updated? What value is used for the current value at this point?

#1 Yes.

#2: No.

#3: No.

#4: It would only take one measurement point, which is not sufficient. The gauge should take at least 4 measurement points for the linear regression to work well, hence the C/10 threshold must be exceeded for 500+3*30 seconds minimum. Note that if you time this to the second, you will not have information about the internal gauge timing as this isn't exposed so you should always add at least one second.

#5: No, the gauge will not update Ra. The gauge takes point measurements and then collects these in a linear regression data structure. It will evaluate (perform the regression through all resistance measurement points as a function of DOD) at an Ra DOD grid point and update Ra at this time.

Hello,

1、Is "ResRelax Time" the register for 500 seconds?

2、What does 500 seconds mean, does the discharge start after 500 seconds, or is it 500 seconds of discharge before the collected current value can be used for 30 second averaging?

3、What is the pattern of 30 second averaging? Do you do an average (moving average) of 30 second intervals at 1 second intervals, or do you average at 30 second intervals?

#1: yes

#2: This means that the gauge needs to be in discharge mode for 500s after it exits relax before the gauge starts to track impedance.

#3: The gauge doesn't use the 30 seconds to average. The gauge uses a first order IIR digital filter on current and voltage to calculate a point resistance measurement every 30 seconds. The gauge doesn't use these measurements directly but instead it performs a linear regression at a DOD grid point through these measurements.

hello Dominik，

Thanks for you reply。

Regarding discharge current：
1. Is the understanding of a and b correct in the following figure?
2. Will RA update immediately after c occurs in the following figure? What is the reason?

Ra will update at the grid point crossing (point c). And it will update in this case because there were 2 measurements that qualified based on current.

1. Is the understanding of point.a and point.b correct in the following figure?

About point b，

2. The current value used at the moment of 30 seconds to calculate RA:

    Is it the average value from the beginning of discharge to the moment of calculating RA?

3、The current value used at the moment of 30 seconds to calculate RA:
    Is the average value from the beginning of 500s of discharge to the moment of calculating RA used?

4、The current value used at the moment of 30 seconds to calculate RA:

   Use the average of the 30 seconds before the moment of the RA is calculated?

5、point.c has only exceeded the C/10 twice, according to the previous description a minimum of 3 consecutive exceedances of the C/10 is required.

Which statement is correct? What's the reason?

Dominik Hartl11 said:

#4: It would only take one measurement point, which is not sufficient. The gauge should take at least 4 measurement points for the linear regression to work well, hence the C/10 threshold must be exceeded for 500+3*30 seconds minimum. Note that if you time this to the second, you will not have information about the internal gauge timing as this isn't exposed so you should always add at least one second.

I think it is probably better to try to work on a specific issue instead of diving into minute details of how the gauge does this. This is going past what I can share on E2E without an NDA.

Hello Dominik,

Background of the question:

Since the discharge current requirement of Bq27426 is >C/10, but the discharge current in our application does not always satisfy >C/10, and the average current does not satisfy >C/10, we would like to make the discharge current >C/10 at the moment of current collection; and keep the original discharge current (maybe <C/10) at the moment of non-collection.

Practical Question:
After Qmax was updated, 5 complete discharges were executed with discharge = Qmax*38%.
Test result: during the 5 complete discharges, RA was updated only once.

I can't share more details on E2E. As there's an internal email thread for this project, I'll have to defer to using email instead.