BQ27426: Could you please help analyze the reason why Qmax has not been updated?

While DOD changes by 0.4, actual passed charge for this to happen is only 419mAh (according to psdchg) or 333mAh (when I calculate this with the reported current and time). Design Capacity is 1230mAh. The gauge also applies a sanity check vs. Design Capacity. 419mAh (if psdchg is right) = 34% of Design Capacity or 333mAh (if calculated with current and time) = 27% of Design Capacity. This usually isn't a problem unless the cell is severely aged (which yours is). You'd have to change Qmax Filter:

DesignCapacity * QmaxFilter / 256 <= passed charge

If passed charge = 333mAh (worse case), then QmaxFilter <= 256 * 333mAh / 1230mAh = 69.

Hello Dominik,

1、passedcharge If the current, voltage and board offset are calibrated during Golden Learning, is it considered error free?

2、Qmax update rule, passedcharge>Qmax*37%, Qmax*37% is calculated by Qmax or design capacity?

3, Qmax update rule, passedcharge>Qmax*37%, is it because Qmax Filtered=96?

4, If the battery ages to 55% before stopping use, the Qmax Filterd value should be changed to 48?

5, Q4 if correct, is passedcharge>230mAh at battery aging >55% enough to make Qmax updated?

6, With the default value of Qmax Filterd=96, at what level of battery aging will the battery no longer be able to self-learn (passedcharge>Qmax*37%)?

7, Will modifying the Qmax Filtered lead to inaccurate Qmax measurement? What other effects are there?

1、passedcharge如果在Golden Learning时，校准了电流、电压及board offset，是不是就可以认为是没有误差？

2、Qmax更新规则，passedcharge>Qmax*37%，Qmax*37%是用Qmax还是design capacity？

3、Qmax更新规则，passedcharge>Qmax*37%，是不是因为Qmax Filtered=96？

4、如果电池老化到55%才停止使用，Qmax Filterd值要改成48？

5、Q4如果正确，电池老化程度>55%时，passedcharge>230mAh就可以使Qmax更新吗？

6、按照Qmax Filterd=96的默认值，电池老化到什么程度，将不能再进行自学习(passedchareg>Qmax*37%)？

7、修改Qmax Filtered，会不会导致Qmax测量不准？还有其它哪些影响？

#1: yes. Note that passed charge reported by the gauge is better than calculating passed charge using current and time from the log file because the latter relies on correct time.

#2: It's relative to Qmax. The gauge uses two DOD0 measurements instead of measuring charge. The difference in DOD must be 0.37. Which is the same, by definition, as 37% of Qmax passed charge.

#3: No. This is another sanity check to avoid erroneous Qmax updates (see the formula that I wrote in my previous reply). This sanity check fails in your example because the very small passed charge isn't due to an erroneous measurement but because you use a significantly aged cell.

#4: This depends on the passed charge that you want to use for Qmax updates. See the formula with Qmax Filter that I wrote in my previous reply.

#5: If passed charge is only 230mAh, then you'd have to set Qmax Filter to: QmaxFilter <= 256 * 230mAh / 1230mAh = 47 (rounded down) to make sure that the gauge won't reject this very small amount of passed charge or a Qmax update, even if DOD changes by > 0.37.

#6: It won't learn Qmax, if DesignCapacity * QmaxFilter / 256 > passed charge, which is, if passed charge < 1230mAh * 96/256 = 462mAh (rounded up).

#7: It will allow Qmax updates with reduced passed charge, which will potentially degrade the quality for the Qmax update (because Qmax = passed charge / change in DOD). So the smaller passed charge, the higher the impact of any absolute error in passed charge measurement on Qmax accuracy.

Hello Dominik，

Thanks for you reply。

1, Fuelgauge performs self-learning, and for Qmax to be updated, both Passedcharge over Qmax*37% and Passedcharge over DesignCapacity*QmaxFilter/256 need to be met?

Dominik Hartl11 said:

#6: It won't learn Qmax, if DesignCapacity * QmaxFilter / 256 > passed charge, which is, if passed charge < 1230mAh * 96/256 = 462mAh (rounded up).

2、If Passedcharge cannot satisfy the Qmax update and the battery continues to be used, will the RA Table still be updated during subsequent aging, and will the FCC still be able to predict the true capacity of the battery?

3, Qmax Filtered 96 modified to 47, can you provide the specific error range?

Dominik Hartl11 said:

#7: It will allow Qmax updates with reduced passed charge, which will potentially degrade the quality for the Qmax update (because Qmax = passed charge / change in DOD). So the smaller passed charge, the higher the impact of any absolute error in passed charge measurement on Qmax accuracy.

4. During the self-learning process, a successful Relax (4uV/s) is required. How to confirm that it has been Relaxed successfully?

Passedcharge=0mAh? or "CONTROL_STATUS[RUP_DIS]=0 and CONTROL_STATUS[VOK]=0"? or Other?

1、Fuelgauge执行自学习，Qmax要更新，需要同时满足Passedcharge超过Qmax*37%和Passedcharge超过DesignCapacity*QmaxFilter/256?

2、如果Passedcharge不能满足Qmax更新，电池继续使用，后续老化过程中，RA Table还会更新吗？FCC还能预测到电池的真实容量吗？

3、Qmax Filtered 96修改为47，是否能提供具体的误差范围？

4、在自学习过程中，需要Relax成功(4uV/s)。如何确认当前已经Relax成功？Passedcharge=0mAh？CONTROL_STATUS[RUP_DIS]=0 and CONTROL_STATUS[VOK]=0？其它？

#1: Yes.

#2: Yes.

#3: This depends on the chemistry and DOD. It's not a simple formula.

#4: The gauge will set OCVTAKEN in Flags() after it detected stable voltage and calculated DOD0. 

Hello Dominik，

1, OCVTAKEN=1, is it indicative of successful Relax with OCV voltage <4uV/s?

2, passedcharge=0, can it be used to determine that RELAX is successful and OCV voltage <4uV/s?

Dominik Hartl11 said:

#4: The gauge will set OCVTAKEN in Flags() after it detected stable voltage and calculated DOD0. 

3、After loading the FS file, the Qmax only needs to be updated once during battery usage and the Fuelgauge will always be able to update the RA Table. is this the right understanding?

Wang Dong said:

2、If Passedcharge cannot satisfy the Qmax update and the battery continues to be used, will the RA Table still be updated during subsequent aging, and will the FCC still be able to predict the true capacity of the battery?

1、OCVTAKEN=1，指示Relax成功，OCV电压<4uV/s吗？

2、passedcharge=0，是否可以用于判断relax成功，OCV电压<4uV/s？

3、加载FS文件后，在电池使用过程中，Qmax只需要更新过一次后，Fuelgauge就一直可以更新RA Table。这个理解对吗？

#1: Yes, but note that this is deferred so the gauge may have taken an OCV measurement earlier than when OCVTAKEN turns 1. But yes, OCVTAKEN means that the gauge qualified the voltage or that the time ran out (5 hours after relax, by default).

#2: This means that the gauge used the OCV reading for a DOD0 update. So yes, this also indicates that the conditions were right (either stable voltage or timeout).

#3: Yes, as long as Qmax is updated, the gauge will be able to update Ra (note that Ra updates still may be disabled by the gauge, if it calculates negative resistance values).

Hi Dominik，

Your support is greatly appreciated。

If the battery does not meet the Qmax update conditions (Passedcharge over Qmax*37% and Passedcharge over DesignCapacity*QmaxFilter/256), and the battery continues to be used, and continues to age, will there be an error in the RA Table that is updated when it is discharged because the Qmax is not updated?What's the reason?

Dominik Hartl11 said:

#3: Yes, as long as Qmax is updated, the gauge will be able to update Ra (note that Ra updates still may be disabled by the gauge, if it calculates negative resistance values).

如果电池的电量不满足Qmax的更新条件(Passedcharge超过Qmax*37%和Passedcharge超过DesignCapacity*QmaxFilter/256)，电池继续使用，继续老化，放电时更新的RA Table会因为Qmax不准确而存在误差吗？原因是什么？

Yes, there will be an error in the Ra table. The reason is that the gauge calculates Ra using the OCV from the cell model and that's a function of DOD, which is a function of Qmax.

DOD = DOD0 + passed charge/Qmax

and conceptually (simplified) Ra = (OCV(DOD,T)-measured voltage)/measured current, compensated for temperature.

Hi Dominik，

1. The OCV voltage of “5 hours after relax” can be used for Qmax update, is that correct?

2、If Q1 is not correct, what is the reason?

Dominik Hartl11 said:

#1: Yes, but note that this is deferred so the gauge may have taken an OCV measurement earlier than when OCVTAKEN turns 1. But yes, OCVTAKEN means that the gauge qualified the voltage or that the time ran out (5 hours after relax, by default).

1、"5 hours after relax"的OCV电压，可以用于Qmax更新，理解正确吗？

2、If Q1不正确，请告知原因？

#2: No, the 5 hours relax timeout is just to force an OCV reading. All other Qmax rules still apply (e.g. flat zone). OCVTAKEN refers to OCV, not Qmax.

Hi Dominik，

Q1, 5 hours Relax timeout, forced acquired OCV, can not indicate OCV stability (4uV/s)?

Q2, 5 hours Relax timeout, forced acquired OCV, can not satisfy the Qmax measurement rule (OCV stable)?

Q3、What is the purpose of the 5-hour timeout?

Q4. What is the meaning of the phrase “Relax until voltage is stable at a high or low DOD (>0.9 or <0.1)” in the Qmax measurement rule?
Q5. According to previous replies, passedcharge=0 can indicate that the OCV is stable. During the learning process, is it true that passedcharge=0, which satisfies the OCV stabilization condition in the Qmax measurement rule?

Q6、During Relax, if “Passedcharge=0 and voltage is not in flat area and temperature 25℃” is satisfied, is it possible to make Qmax measurement?

1、5小时Relax超时，强制获取的OCV，不能表示OCV稳定(4uV/s)吗？

2、5小时Relax超时，强制获取的OCV，不能满足Qmax测量规则(OCV稳定)？

3、5小时超时的目的是什么？

4、Qmax测量规则中"Relax until voltage is stable at a high or low DOD (>0.9 or <0.1)"，这句话如何理解？

5、根据以前的答复，passedcharge=0，可以表明OCV稳定。学习过程中，是不是passedcharge=0，就能满足Qmax测量规则中的OCV稳定条件？

6、Relax期间，满足“Passedcharge=0 and 电压不在平坦区域 and 温度25℃”，是不是就可以进行Qmax测量？

#1: Correct.

#2: The stability rule is over-ruled after 5 hours (exceptions apply) so if all other Qmax update rules are met, the gauge will update Qmax after it took an OCV measurement after 5 hours.

#3: Some systems have a quit current that's relatively high so if the voltage keeps dropping in relax, it may never meet the voltage stability requirement. It's important for the gauge to have high quality DOD so if you have a system where voltage stability cannot be met, it's better for DOD to be updated after a long time in relax (where by definition the current is low) that having DOD that gets worse due to accumulated measurement errors.

#4: This loosely refers to the rule that OCV must be outside a flat zone, which is usually the case for DOD <0.1 or >0.9. The actual DOD numbers are indirectly given with Q Invalid Min/Max V.

#5: Passed charge = 0 means that the gauge took an OCV measurement and qualified this for a DOD update. It does not mean that the gauge updated Qmax. But it's a requirement for Qmax updates.

#6: Yes, if total DOD change satisfies the min. DOD percent for Qmax update and it didn't take too long for accumulated passed charge errors to exceed the max. limit for Qmax updates and if all other Qmax update rules are met.

Hi Dominik，

In the “TI Power Meter Application Guide” provided by FAE, the Qmax update is described as follows:

Offset Error, the bias error accumulates no more than DF:Design Capacity × 1%, calculated as Offset error current = DF:Coulomb Counter Deadband / sense resistor from the last OCV sampling to the current integration value.
DF: Coulomb Counter Deadband is the threshold for Coulomb integration. Above this threshold is considered normal load current integration, below it is considered offset error.

1, Offset Error, is the passedcharge error.Is this a correct understanding?

2, At the beginning of Golden Learning, after calibrating the device for current, voltage, and board, the error will not exceed 1%.Is this a correct understanding?

在FAE提供的"TI电量计应用指导"中，关于Qmax更新，有如下描述：

Offset Error，偏置误差累积不超过DF:Design Capacity ×1%，计算方法是Offset error current = DF:Coulomb Counter Deadband / sense resistor 从上一次 OCV 采样到现在的积分值。
DF:Coulomb Counter Deadband 是库仑积分的门限。高于该门限则视为正常负载电流积分，低于该门限则视为 offset error。

1、Offset Error，是指的passedcharge误差，这个理解正确吗？

2、在Golden Learning开始时，对设备进行电流、电压、board校准，是不是误差就不会超过1%？

1: The gauge's coulomb counter has an offset-error. This offset error, over time, will cause unacceptable error in passed charge. So if the time between two OCV measurements is too long, the total accumulated offset error will lead to the gauge disqualifying the Qmax update. The exact formula is not what you stated and it's not public. It's usually only a problem if you wait days between two OCV measurements, hence it's a Qmax update rule for a rare use case and not published.

2: Yes. See #1.

Hi Dominik，

Q1, Too much time between two OCV measurements can cause Offset Error.
What is the long time, exactly how many days?

Q2, What is the meaning of “not published”, Bq27426 is not effective?

Dominik Hartl11 said:

1: The gauge's coulomb counter has an offset-error. This offset error, over time, will cause unacceptable error in passed charge. So if the time between two OCV measurements is too long, the total accumulated offset error will lead to the gauge disqualifying the Qmax update. The exact formula is not what you stated and it's not public. It's usually only a problem if you wait days between two OCV measurements, hence it's a Qmax update rule for a rare use case and not published.

Q3、How to determine the current offset-error meets no more than Design Capacity*1%?

Q4、Is there a register to indicate the current offset-error?

Q1、两次OCV测量间隔时间太长会导致Offset Error。长时间，具体是多少天？

Q2、"not published"是什么意思？Bq27426不生效？

Q3、如何判断当前offset-error满足不超过Design Capacity*1%？

Q4、是否有寄存器可以指示当前的offset-error？

Hello Dominik，

1, Has the email been sent to FAE yet? I haven't received a reply from FAE yet.

2, CC Offset will change from 0 to 1 during use.Will this satisfy <Design Capacity*1%?

3、Can you please help to calculate the CC Offset value equal to how much it means the Offset Error exceeds Design Capacity*1%?

Dominik Hartl11 said:

3: See #1. I'll share more details via e-mail with the FAE that works with you.

1、邮件发送给FAE了吗？我还没收到FAE的回复。

2、在使用过程中CC Offset会从0变为1.这个能满足<Design Capacity*1%吗?

3、请帮忙计算下，CC Offset值等于多少时，说明Offset Error超过了Design Capacity*1%？

Hello Wang,

Dominik is out today, he will get back to you next week.

Regards,

Nick Richards

Hello Dominik，

Please help to confirm the above, thanks!

I'll email it to the internal thread again today.

Hello Dominik，

FAE did not receive your email.

Can you directly state the conclusion of the following two questions, and synchronize the judgment method email to FAE?

1、CC Offset will change from 0 to 1 during use.Can this satisfy <Design Capacity*1%?

2、Please help me to calculate when CC Offset value is equal to what, it means Offset Error exceeds Design Capacity*1%?

FAE没有收到您的邮件。

能不能在E2E上直接说下下面两个问题的结论，并把判断方法同步邮件给FAE？

1、在使用过程中CC Offset会从0变为1.这个能满足<Design Capacity*1%吗?

2、请帮忙计算下，CC Offset值等于多少时，说明Offset Error超过了Design Capacity*1%？