BQ27426: Correction conditions for Filtered RM

Hello,

This question has been assigned and will be reviewed when possible.

Thank you,
Alan

#1: True RM will change every 5deg.C (default). Filtered RM (in relax) will follow TrueRM, if RelaxRCJumpOk in OpConfigB is set to 1.

#2: No. The moment that the gauge detects a change of temperature 5deg.C it will run a simulation and update TrueRM. If the cell is relaxing and RelaxRCJumpOK is set to 1 then Filtered RM will change at the same time.

#3: SMOOT_SYNC command, VCT and Terminate Voltage.

HI Dominik，

1、Relax状态通过哪个寄存器可以确认？OCVTAKEN？

2、VCT是什么意思？

3、当TRUE RM=0时，TRUE RM会不会赋值给FilteredRM？

1、Which register can be used to confirm the Relax state? Is it OCVTAKEN?

2、What does VCT stand for?

3、When TRUE RM equals 0, will TRUE RM be assigned to Filtered RM?

#1: The best method is to check DOD passed charge. It will clear to 0 after a successful OCV measurement that qualifies for cell state update (and which results in a true RM update).

#2: Valid Charge Termination. This is when the gauge detects a full charge.

#3: It's the other way round. Filtered RM will be set to True RM if True RM is set to 0 due to a simulation or voltage dropped below Terminate Voltage during discharge. It may not be set to 0 if True RM counts down to 0 because of coulomb count.

Hi dominik，

#1、Passedcharge=0期间，可以确认为静置成功？这个期间温度变化超过5℃，Filtered RM会更新？

#3、不太理解这句话，特别是最后一句，能不能详细说明下?

#1: Yes, if DOD passed charge changes to 0 then the gauge took an OCV measurement. If RelaxRCJumpOK is set to 1 then the gauge will automatically sync filtered values to true values if temperature changes by (default) 5deg.C.

About #3: The gauge FW doesn't set unfiltered(true) values to filtered values but it's the other way around. It will, under certain conditions, set filtered(smoothed) values to unfiltered(true) values. For example, if the gauge is in discharge mode and voltage drops below Terminate Voltage, then the gauge will force both unfiltered(true) and filtered(smoothed) RM and SOC to 0mAh and 0%.

HI Dominik，

还是不太理解。

增加场景：

长周期测试，保持Relax模式，FilteredRM初始值300mAh，TRUE RM初始值300mAh。

Filtered RM间隔3小时自增1mAh。

电池自损耗，TRUE RM值持续下降。

假如，TRUE RM=1mAh时，Filtered RM=600mAh。当TRUE RM=0mAh时，Filtered RM会变为0mAh吗？

Sorry，I still don't quite understand.

Scenario Added:

Long-term testing, maintaining Relax mode, initial Filtered RM =300mAh, initial TRUE RM=300mAh.
Filtered RM self-increments by 1mAh every 3 hours.
Due to battery self-discharge, the TRUE RM value continuously decreases.
Hypothetically, when TRUE RM = 1mAh, Filtered RM = 600mAh. When TRUE RM = 0mAh, will Filtered RM become 0mAh?

Filtered RM will be set to 0mAh if True RM is 0mAh due to a simulation event (not due to coulomb count).

HI Dominik，

根据您的回复，我描述的场景，True RM=0时，Filtered RM也会为0mAh.

理解对吗？

Based on your reply, in the scenario I described, when True RM = 0mAh, Filtered RM will also be 0mAh.

Is this understanding correct?

Only if this is due to a simulation. Not if this is due to a simple coulomb count.

HI Dominik，

温度变化超过5℃，且FuelgaugeIC处于relax mode时，FilteredRM会仿真、更新。

在什么时候获取初始的温度？passedcharge=0的时刻吗？

5℃的变化需要在passedcharge=0期间吗？

When the temperature changes by more than 5∘C and the Fuel Gauge IC is in relax mode, the Filtered RM will undergo simulation and update.

1、When is the initial temperature reading taken? Is it at the moment passedcharge = 0?

2、Does the 5∘C change need to occur while passedcharge = 0?

#1: It's taken at the first simulation trigger, for example right after SOFT_RESET.

#2: No.

HI Dominik，

我们在测试过程中，

发现温度上升超过5℃，TRUE RM下降；温度下降超过5℃，TRUE RM上升。

1、这属于正常现象吗？为什么？

2、另外在附件的sheet[test2]中，还出现了温度变化超过5℃，但Filtered RM未修正为TRUE RM的情况？为什么？ 

During our testing, we found that TRUE RM decreases when the temperature increases by more than $5℃$, and TRUE RM increases when the temperature decreases by more than $5℃$.

1、Is this a normal phenomenon? If so, why?

2、Additionally, in the attached sheet [test2], a situation occurred where the temperature changed by more than $5℃$, but the Filtered RM was not corrected to TRUE RM. Why is that?

Test of TRUE RM Change with Temperature Variation.zip

#1: It looks like this chemistry significantly adjusts DOD0 at high grid points, which impacts True RM in the way that you observe. 

The gauge models cell behavior with OCV(DOD, T) and R(DOD, T). R usually decreases with temperature rising. Therefore, if you see True RM falling with a rise in temperature, like in this case, it's not due to R but as we can see here, it's due to DOD(OCV, T).

#2: The gauge will override the auto-sync if the trigger for a simulation was time (every one hour in relax by default).

HI Domink，

关于问题#1，不理解您的回复。

1、正常情况下，温度升高，放电量多还是温度下降放电量多？

如果温度升高，放电量多，那么RM不应该减少。

如果温度下降，放电量多，请告知原因、机理？

2、上一个case的测试温度范围为25~46℃。

在14℃~26℃的温度范围内进行测试，呈现的现象是温度升高，TRUE RM升高，温度下降，TRUE RM下降。与预期的结果相符。请查看附件sheet[T14-26]

两者有什么区别？与CHEMID的温度修正有关吗？请帮忙解惑，谢谢！

关于问题#2,1小时在资料中未看到过，来源能否提供下？1hours是静置成功(dV / dt < 4 µV/s)的超时时间吗？

Regarding Question #1,I do not fully understand your reply.

1、Under normal circumstances, does a temperature increase or a temperature decrease result in more discharge capacity?

If a temperature increase results in more discharge capacity, then $\text{RM}$ should not decrease.

If a temperature decrease results in more discharge capacity, please explain the reason and mechanism.

2、The testing temperature range for the previous case was $25℃\sim 46℃$.

In the temperature range of $14℃\sim 26℃$, the phenomenon observed was that $\text{TRUE RM}$ increased with a temperature increase and $\text{TRUE RM}$ decreased with a temperature decrease, which is consistent with the expected result.

Please check the attachment sheet [$\text{T}14-26$].

2-1、What is the difference between the two cases?

2-2、Is it related to the $\text{CHEMID}$'s temperature correction? Please help clarify, thank you!

Regarding Question #2:

We have not seen the $one\text{ hour}$ value in the documentation. Can you provide the source for this? Is $one\text{ hour}$ the timeout period for a successful $\text{relax}$ state ($\text{dV}/\text{dt}<4\mu \text{V}/\text{s}$)?

5355.Test of TRUE RM Change with Temperature Variation.zip

#1 depends on DOD and how the gauge models OCV for a given DOD. The previous example modeled higher DOD for rising temperature, hence True RM dropped. Therefore the effect changes with DOD and with ChemID.

#2: There are many details of the algorithm that are not documented. I studied the firmware to answer your question so the source of my answer is in the actual source code. It has a time threshold (default 1 hour), which will override the temperature triggered simulation and because of this override, it also overrides the RCJumpOk sync of filtered and true values for this particular simulation trigger.

Dear Dominik，

关于温度超过5℃时，Filtered RM修正，有三个疑问：

1、判断当前温度是否超过5℃的Base温度，在初次上电时获取，在使用过程中，base温度是否会发生变化？

2、我们分析测试日志，发现每次TRUE RM更新时，base温度就会发生变化。是否正确？

3、Base温度在哪些场景下会更新为当前温度？

关于温度超过5℃时，Filtered RM修正，有一个疑问：

4、当温度上升，DOD0、Ra、OCV和TRUE RM这四个量，是如何变化的？请帮忙提供变化曲线图示？

Regarding the Filtered RM correction when the temperature exceeds 5∘C, I have three questions:

1、The Base temperature, used to determine if the current temperature exceeds 5∘C, is acquired at the initial power-on. Does the Base temperature change during usage?

2、We analyzed the test logs and found that the Base temperature changes every time the TRUE RM is updated. Is this correct?

3、In which scenarios will the Base temperature be updated to the current temperature?

Regarding the Filtered RM correction when the temperature exceeds 5∘C, I have one question:

4、When the temperature increases, how do these four quantities—DOD0, Ra, OCV, and TRUE RM—change? Could you please provide a graph or illustration of their change curves?

#1: The "base" temperature is the temperature when the gauge ran the previous simulation. The first time is usually after it received the SOFT_RESET command.

#2: Correct.

#3: When there's a simulation.

#4: DOD0 depends on chemistry. Ra is, by definition, independent of temperature. R typically rises with lower temperatures and vice versa. True RM usually decreases with lower temperatures (but it may go up, depending on chemistry and load prediction).

HI Dominik，

1、Base Temperature为什么在True RM仿真时更新为Now temperature？机制是什么？目的是什么?

2、如果温度在缓慢变化(如1小时仅变化1℃)，RM自增间隔3个半小时，是不是Filtered RM就无法更新为TRUE RM值了？

3、如果2成立，除了SMOOTH_SYNC指令外，还有其它办法可以是Filtered RM更新为TRUE RM值吗？

4、如果2不成立，请告知为什么？

1、Why is Base Temperature updated to Now temperature during True RM simulation? What is the mechanism, and what is the purpose?

2、If the temperature is changing slowly (e.g., only 1∘C per hour), and the RM self-increment interval is $3.5$ hours, will Filtered RM be unable to update to the TRUE RM value?

3、If question 2 is Yes, besides the SMOOTH_SYNC command, are there any other methods that can update Filtered RM to the TRUE RM value?

4、If question 2 is No, please explain why.

Can you please explain why you need this level of detail? This forum is not intended to fully explain every minute detail of a TI product but to resolve problems that customers may have.

If you have a specific problem, please post it and TI will answer.

HI dominik，

理解您的回复。我们只有了解了机制，才能根据机制，分析对我们产品的影响。如涉及知识产权，直接告知我们就可以了。

下面的问题应该不牵扯IC算法细节，请帮忙回复下，

1、如果温度在缓慢变化(如1小时仅变化1℃)，RM自增间隔3个半小时，是不是Filtered RM就无法更新为TRUE RM值了？

2、如果2成立，除了SMOOTH_SYNC指令外，还有其它办法可以是Filtered RM更新为TRUE RM值吗？

3、如果2不成立，请告知为什么？

I understand your reply. Only by understanding the mechanism can we analyze its impact on our product based on that mechanism. If intellectual property is involved, please just inform us.

The following questions should not involve IC algorithm details. Please help to answer them:

1. If the temperature changes slowly (e.g., only 1∘C change in one hour), and the RM auto-increment interval is $3.5$ hours, will the Filtered RM be unable to update to the TRUE RM value?

2. If the answer to question 1 is "yes" (that the Filtered RM cannot update), are there any other methods besides the SMOOTH_SYNC command that would allow Filtered RM to update to the TRUE RM value?

3. If the answer to question 1 is "no" (that the Filtered RM can update), please let us know why?

#1: Once the total temperature change exceeds 5deg.C, the gauge will auto-sync when it re-simulates True RM. If the interval is 3.5 hours for RM to increase by 1mAh then you'll see an increase in RM until the temperature changed enough.

#2: The answer was technically "no" because filtered RM will update eventually once temperature increases enough.

#3: It will update after 5 hours so while you will see a bit of an increase in filtered RM after 3.5 hours, it'll sync after 5 hours if temperature changes by 1 deg.C per hour.

HI dominik，

非常感谢您的支持。

1、RM自增是因为Passedcharge=-1mAh，即间隔3个半小时，passedcharge会变为-1mAh。

当passedcharge从1mAh变为0mAh时，TRUE RM会重新仿真，此时Tbase会发生更新Now Temperature。

所以我认为，如果在两次TRUE RM仿真之间，温度变化未超过5℃，Filtered RM不会因为温度变化超过5℃的原因，更新为TRUE RM。

这个理解是否正确？

2、RM自增的间隔是固定的吗？RM自增间隔时间会不会因为温度、SOH等因素，发生变化？

Thank you very much for your support.

1、The RM self-increment is because PassedCharge = -1mAh, meaning that passedcharge changes to -1mAh every 3.5 hours.

When passedcharge changes from -1mAh to 0mAh, TRUE RM will be re-simulated, and at this time, T_base will be updated to Now Temperature.

Therefore, I believe that if the temperature change does not exceed 5℃ between two TRUE RM simulations, the Filtered RM will not update to the TRUE RM value due to the temperature change exceeding 5℃.

Is this understanding correct?

2、Is the interval for RM self-increment fixed? Will the RM self-increment interval change due to factors like temperature, SOH (State of Health), etc.?

#1: A simulation doesn't necessarily update the filtered values. The filtered values are only updated if this simulation is triggered by a temperature change.

#2: No, the rate depends on the noise of the coulomb counter. This is different between parts and also a function of environment (e.g. temperature and voltage).

HI dominik，

1、关于A1，也就是说我的问题的回复是yes?两次TRUE RM仿真之间，温度变化需要超过5℃，Filtered RM才会被修正为TRUE RM。

2、关于A2，温度与自增间隔的关系是什么？温度升高，自增间隔会增加还是减少？有没有温度和自增间隔的具体的系数？

3、关于A2，在不能自学习的场景下，直接插入新电池和老化电池，发现老化电池的RM自增间隔比较大(大概11个小时自增一次)，新电池的RM自增间隔比较小(大概3个半小时自增一次)。这个结果是正常的吗？为什么？

4、有没有SOH和自增间隔的具体的系数？

1、Regarding A1, does that mean the answer to my question is yes? The temperature change needs to exceed 5℃ between two TRUE RM simulations for the Filtered RM to be corrected to the TRUE RM.

2、Regarding A2, what is the relationship between temperature and the auto-increment interval? When the temperature increases, does the auto-increment interval increase or decrease? Are there specific coefficients for the relationship between temperature and the auto-increment interval?

3、Regarding A2, in a scenario where self-learning is disabled, when a new battery and an aged battery are inserted directly, it is observed that the aged battery's RM auto-increment interval is relatively long (autoincrements about once every 11hours), while the new battery's RM auto-increment interval is relatively short (autoincrements about once every 3.5 hours). Is this result normal? Why?

4、Are there specific coefficients for the relationship between SOH and the auto-increment interval?

1: Yes, this needs a temperature change to sync.

2: This depends on the internal characteristics of the CC ADC circuitry for a specific gauge (it varies from gauge to gauge). Note that this is a subtle effect on the CC ADC level - the problem is with the way that the gauge FW handles the noise, which can cause an incorrect current. If the noise spectrum is a bit different from gauge to gauge, temperature to temperature, you'll get a different "step" size for the erroneous charge.

3: I don't know. This is probably due to differences in cell voltage. Are both cells charged to exactly the same OCV?

4: No.

HI Dominik，

1、针对我们使用的BQ27426，RM自增间隔与温度和SOH的关系是什么趋势？RM自增间隔最短的场景(温度、SOH)是什么？

2、劣化电池自增间隔长的测试，电池电压相差仅2mV，和电压应该关系不大。还有其它可能的原因吗？

1、Regarding the BQ27426 we are using, what is the trend of the relationship between the RM self-increment interval and Temperature and SOH? What is the scenario (Temperature, SOH) where the RM self-increment interval is the shortest?

Dominik Hartl11 said:

2: This depends on the internal characteristics of the CC ADC circuitry for a specific gauge (it varies from gauge to gauge). Note that this is a subtle effect on the CC ADC level - the problem is with the way that the gauge FW handles the noise, which can cause an incorrect current. If the noise spectrum is a bit different from gauge to gauge, temperature to temperature, you'll get a different "step" size for the erroneous charge.

2、In the relax test where an aged battery has a longer self-increment interval, the initial battery voltage difference is only 2mV, suggesting minimal correlation with voltage. Are there any other possible reasons?

zhangjin said:

3、Regarding A2, in a scenario where self-learning is disabled, when a new battery and an aged battery are inserted directly, it is observed that the aged battery's RM auto-increment interval is relatively long (autoincrements about once every 11hours), while the new battery's RM auto-increment interval is relatively short (autoincrements about once every 3.5 hours). Is this result normal? Why?

#1: This depends on process variations from chip to chip. The higher the temperature, the more likely that noise will be a problem, causing RM to change over time.

#2: This isn't related to the age of the cell but to the supply voltage of the gauge.

HI Dominik，

我们电池的使用温度是10℃--75℃。能提供RM自增间隔最短的场景吗？

The operating temperature range for our battery is 10℃to 75℃. Could you provide the scenario where the shortest RM self-increase interval occurs?

Most likely at 10deg.C

Hi Dominik,

我们实测的结果是高温+新电池场景是最短的RM自增间隔。常温+老化电池场景是最长的RM自增间隔。

1、这属于正常现象吗？

2、RM自增的间隔在不同温度环境下是线性的吗？

Our measured results show that the shortest RM self-increment interval occurs in the high-temperature + new battery scenario.

The longest RM self-increment interval occurs in the normal-temperature + aged battery scenario.

1、Is this considered normal behavior?

2、Is the RM self-increment interval linear across different temperature environments?

The coulomb counter noise, which is the root cause for the increase over a long period of time should be less at lower temperatures. As the accumulation over a long amount of time is a known behavior and TI addressed this with the SMOOTH_SYNC command, it's considered part of the gauge's behavior.

I don't know if it's linear over temperature.

HI Dominik,

能否通过实测或理论分析，给出RM最短自增间隔的极限条件？我们需要根据这个条件，来分析对市场产品的影响。

Could you please provide the extreme conditions for the minimum increment interval of RM through actual measurement or theoretical analysis?

We need to analyze the impact on market products based on these conditions.

HI Dominik，

结合我们的应用，罗列了RM最短自增间隔的测试项，请帮忙确认：我们罗列的测试项是否可以测出RM最短自增间隔时间？还需要哪些FuelgaugeIC的参数？

应用温度： Min 10℃，Max 74℃

SOH：电池寿命终结=65%

RM值：

694mAh--->电池最大充电容量；

632mAh--->电池容量，低于632mAh时，启动充电到694mAh；

98mAh--->电池放电时，停止放电的容量

We have listed the test items for determining the shortest RM self-increment interval based on our application. Could you please help us confirm the following:

1、Can the listed test items effectively measure the shortest RM self-increment time?

2、What additional Fuel Gauge IC parameters are required?

Application Parameters:

• Battery Temperature Range: Min 10℃, Max 74℃

• SOH Threshold: Battery End of Life (EoL) = 65%

• RM (Remaining Capacity) Values:

  • 694mAh to Maximum Charge Capacity (Full Charge Capacity when new)

  • 632mAh to Battery Capacity threshold; charging starts when the capacity drops below 632mAh (and charges back up to 694mAh).

  • 98mAh to Capacity at which discharging stops.

Best regards!

I don't understand the request. I don't have data about the shortest RM self-increment time for different temperatures. The self-increment is an artifact of the smoothing algorithm and a part-part variation of offset error.

The official recommendation is to either disable smoothing (the gauge will then self-correct automatically at every OCV measurement) or sending the SMOOTH_SYNC command after a long time in relax where filtered RM may increase by a few mAh.

Hi Dominik,

感谢你的支持。

没有相关的数据，我们了解了。

现在我们想基于设备的使用场景，通过测试进行RM自增间隔的极限值确认。

之前有说过温度对RM自增有影响，结合我们的实测结果，我们认为通过电压、温度、健康度这三个因素的矩阵测试，可以测试出极限值。

请帮忙确认，是否正确？

Thank you for your support.

We understand that you do not have the relevant data.

Now, we want to confirm the limit value for the RM self-increment interval through testing based on the device's usage scenarios.

It was previously mentioned that temperature affects RM self-increment. Combined with our actual measurement results,

we believe that a matrix test covering these three factors—"Voltage, Temperature, and SOH"—can determine the limit value.

Could you please help confirm if this approach is correct?

Hello Zhangjin,

Are you in a email thread with Dominik on this?

-Miguel

HI Miguel，

没有固定为Dominik，只是这个Thread之前一直是Dominik回复的。

TI其它人员帮忙确认问题，也是可以的。

It’s not limited to Dominik; it’s just that Dominik has been the one replying to this thread so far.

It’s also fine if other team members from TI can help confirm the issue.

HI TI Team，

We have not yet received a reply to the aforementioned questions. Could you please respond as soon as possible? Thank you!

I do not know if this approach is correct. TI doesn't have the bandwidth to support your deep analysis of this system. Please use the SMOOTH_SYNC command as recommended, which is the official solution from TI.

HI TI Team，

Thank you for your detailed responses earlier!

From our previous communication, we understand that RM self-increment is related to coulomb counter noise, which is influenced by temperature and voltage.

We would like to further confirm:

besides temperature and voltage, what other parameters does TI refer to when analyzing and verifying coulomb counter noise?

Dominik Hartl11 said:

#2: No, the rate depends on the noise of the coulomb counter. This is different between parts and also a function of environment (e.g. temperature and voltage).

感谢此前的详细回复！

根据之前沟通，已知 RM 自增与库仑计噪声相关，且库仑计噪声受温度、电压影响。

想进一步确认：TI 在分析、验证库仑计噪声时，除了温度和电压，还参考了哪些参数？

The gauge uses an internal algorithm (a non-linear filter using various thresholds) to analyze and gate the noise. They are private parameters and not shared.

This problem will have to be handled with SMOOTH_SYNC, which is a fully validated. There is no other TI-endorsed method.

HI Dominik，

Thank you for your support.

We understand that you cannot provide specific parameters as they involve TI’s patents.

1、Regarding the noise mentioned in our previous communication being a function of the environment (temperature and voltage), can we understand that temperature and voltage are the main factors affecting the RM auto-increment interval? Are other factors negligible due to their small impact?

2、Additionally, regarding the mentioned differences between parts, does "parts" refer to individual ICs or different batches of ICs? Are differences between parts a major factor?

Dominik Hartl11 said:

#2: No, the rate depends on the noise of the coulomb counter. This is different between parts and also a function of environment (e.g. temperature and voltage).

感谢支持。

具体参数涉及到TI的专利无法回复，我们了解了。

1、之前沟通的噪声是环境(温度、电压)函数，是不是可以理解为温度和电压是影响RM自增间隔时间的主要因素？其它因素占比很小，可以忽略？

2、另外，提到的不同parts有差异，不同parts是指单个IC还是不同批次的IC？parts差异是主要因素吗？

I do not have more information about this topic. Please use the TI recommended method: Send SMOOTH_SYNC after a significant amount of time in realx.