How to prevent

Release date：2016-12-16   Views：2483

In 2016, the most lively mobile phone market was related to battery news. Whether it's the oppo fever brought about by "charging for 5 minutes and calling for 2 hours", or the explosion of Samsung Galaxy Note7 battery, and the Apple iPhone 6S coming out at the end of the year, all these are related to the battery. To be more specific, they are all related to the battery management chip scheme. Despite a small battery and charging, around his chip management, but there is a lot of learning, especially when we increase the charging power to more than 15W, next year the flagship will go to 28w, which will bring various security risks.

Next, Chang Xu invited Jiang Yanbo, CEO of Saiwei electronics, the leading manufacturer of battery management chips in China, to tell you the story in this respect, analyze several major events that made people panic in 2016, and predict several major technological breakthroughs in mobile phone battery management in 2017.

 

Before you tell a story, read a simple structure diagram around the battery management of mobile phones, because all the stories (accidents) that follow are related to it.

 

Here, the core is the charge management IC, which manages all charging behaviors, i.e. trickle / constant current / constant voltage control required by lithium battery. Because it is based on the DC / DC architecture for voltage and current conversion, when the charging power is higher, the above loss will be greater. The other is the IC, which is a special ASIC device, which is used to track the battery power and internal resistance in real time, and calibrate the battery power. The trend is that more and more solutions will move the electricity meter to the circuit board of the battery pack, and the customization of the battery pack is more and more high-tech; the third is the battery protection IC in the battery pack, which is used as over discharge, overcharge and over-voltage The battery protection IC will control the MOS on the battery protection board to turn off the charging and discharging circuit to ensure the safety of the battery in case of various battery abnormal conditions. There is also a battery simulation front-end and authentication IC, which is located in the battery pack to monitor the battery in real time, and uses encryption algorithm to authenticate the true and false batteries. Whether it is the battery pack side meter IC or the battery simulation front-end and authentication IC, they can "closely monitor" the battery pack inside the battery pack, monitor the changes of various physical parameters of the battery in real time, and manage the charging and discharging point behavior by communicating with the host computer. If this mechanism fails, it will cause big problems in the case of fast charging. This year will be analyzed later The most typical case.

 

To do the above battery management IC well, we should not only understand the electronic technology, but also be familiar with the battery electrochemical technology. It is a combination of these two technologies. Therefore, there are not many players here, especially the electricity meter. There are basically three companies: Ti, Meixin and China's Saiwei electronics. Among them, Ti is also a supplier of apple (known from the sudden shutdown of the iPhone 6S) and more than 80% of the mainstream mobile phone suppliers, except Samsung. Samsung's supplier is Mercure (we will analyze the cause of Samsung note 7 accident later). China Xinxing Weiwei is the power meter supplier of some mobile phones of Hongmi, ASUS, LETV and ZTE. In addition, the three pins are completely incompatible. Here, Ti has applied for many patents in battery meter technology.

It is very important to add that we need to define fast charging. How to call it "fast charging"? In fact, it is an abstract concept relative to slow. For example, 5V 2A (10W, some use 9V 1.2A) was fast charging two years ago, but this year, it became standard, so we don't call it real fast charging. Next year, the 5V 3A supported by type C will also become the standard configuration, and the high-end flagship computers of all manufacturers may be faster than type C, that is, higher than 15W. Therefore, we are talking about the various security risks and solutions that mobile phone manufacturers use when they use higher charging power than the industry standard typec. At the same time, we will also talk about how the mobile power supply (i.e. the power bank) can provide the identification and support of fast charging technology for these complicated "fast charging" mobile phones.

 

Well, with these basic concepts, we begin to tell the story of fast charging and the "accidents" it caused in 2016, and how to prevent the various disasters caused by these fast charging in 2017. By the way, we have to analyze, is it possible for apple to use radical fast charging? Why?

Comparison of two "heat reduction" schemes for fast charging

"Direct charging and fast charging" and "dual charging management IC"

We divide the charging management into two stages: the first stage is from the adapter to the USB port of the mobile phone; the second stage is from the USB port of the mobile phone to the charging management and battery protection control of the battery.

Traditionally, the adapter outputs a 5V power supply to the mobile phone. The charging management IC in the mobile phone converts it into the power required by the battery terminal voltage. After the 5V voltage is reduced, a constant current / constant voltage power supply is generated to supply power to the battery. This conversion is efficient. Why is there a big technical threshold for fast charging above 15W? Because the highest efficiency of this DC / DC is Ti, which is 91% efficiency. The high current may be 90%. This mapping shows that when 15W is charged, the dissipated power on DC / DC reaches 1.5W, and the mobile phone will be hot.

Three years ago, oppo adopted a new idea to solve the heating problem of the fast charging mobile phone. Three years ago, oppo adopted a new idea. The DC / DC step-down work was put into the adapter side, so that the charging management function was completed by the adapter. The adapter directly generates a constant current source to charge the battery core, bypassing the charging management IC in the mobile phone. In this way, the mobile phone terminal will not get hot. However, due to the large space of the adapter, the heat dissipation is fast The heat won't be serious. In the vooc fast charging scheme, the mobile phone has a physical switch. What current is coming is directly transmitted to the battery, so the mobile phone will not be heated due to DC / DC heat consumption. The mobile terminal of vooc solution only has a conventional Ti battery management IC, which supports 2A charging. When it is fast charging, it will pass through. When it is near full, it will switch to the Ti chip through a switch, and then continue to charge the battery with a current of 2A.

 

This is what the industry calls "fast charging through". Oppo has applied for hundreds of patents for this technology. This solution is popular because consumers don't feel the excessive heating of mobile phones. Later, MTK's pe3.0 fast charging standard also supports similar direct charging technology. Huawei's latest mate 9 may also use similar technology, but the details are different. Let's talk about it later. This kind of plan will be adopted by more and more companies. Many companies are lining up their troops on the direct charging scheme. I don't know how oppo can hold the city here.

So, there is another school of technology called "cooling down.". In order to reduce the heat of the mobile phone charging more than 15W, another technology school is the parallel charging technology mainly promoted by Ti at present: the fast charging of more than 15W adopts two DC / DC charging management IC, because the power of each is smaller, the efficiency is improved, the heat dissipation area is larger, and the heating is smaller. At present, the latest fast charging mobile phones such as vivo and Meizu use TI parallel charging technology. This kind of technology is not like "direct charging", which is a cross era change, but also a kind of "mending the wall" scheme. However, this scheme is still hot. The constraint of this scheme is that the charging current reaches 5a, that is, more than 24W, there will still be problems. However, due to the "direct charging" scheme oppo has applied for many patents, other manufacturers will have access barriers.

"Next year, the typec interface will be unified. First, MTK's pe3.0 is based on the physical interface of typec, which is the first to follow; second, the latest qc4.0 of Qualcomm also indicates that it is compatible with typec PD protocol. " Jiang Yanbo, CEO of Saiwei electronics, explained, "therefore, we expect that from 2017 to 18, mainstream mobile phones from the middle to the high end will directly adopt typec's 15W (5V 3a). When the charging management IC efficiency is very high, the mobile phone's heating will be similar to the current 5V 2a, which is acceptable." "So, without the need for direct charging, type C based charging can meet the requirements of most mobile phones," he said. But if we want to achieve more than 20W, we have to use dual charging management IC scheme. " He said that for a typical typec solution, xevi can provide a DC / DC charging management IC with a 93% efficiency, which has been adopted by mobile phone manufacturers and can be mass produced in the first quarter of 2017. Jiang Yanbo also explained why they were able to achieve 93% efficiency: first, the contribution of the special process cooperating with the OEM factory; second, the improvement of Saiwei in the back-end processing, adopting innovative packaging process, combining the front-end with the back-end, the internal resistance of the charging management IC is very small, so the efficiency is improved.

This year, the mainstream of midrange models is 5V 2a, and the next year is 5V 3a. Because of the ecological chain support of typec, the cost of charging management IC, terminals, wires and adapters will be greatly reduced. However, the flagship opportunity of pursuing extreme fast charging will go to 25-30w, such as mate9, super vooc, etc. So, how much can the charging speed be increased from 5V 3a to 28w (5V 5.6A) at such a high price? Jiang Yanbo simply calculated: according to the battery at 4000ma, 5V 3A can be fully charged in about 90 minutes; if it is replaced by 28w (5V 5.6A), it will be fully charged in about 60 minutes.

However, after Samsung's battery incident, everyone's speed toward fast charging has slowed down.

 

The Samsung note 7 accident is not just about batteries

At present, several conjectures about the Samsung Galaxy Note7 battery accident have won more and more people's approval for the statement that "the design of the battery compartment is too radical", because after the radical design of the battery compartment, when there is a slight elastic change, it will squeeze and cause short circuit. However, some experts in Chang Xu's interview said that it was not only the battery problem, but also the design of charging management IC. If the protection of battery management scheme is well done, charging can be terminated when most batteries are abnormal, so as to reduce the probability of safety accidents.

"So, part of Samsung's problem may be due to the charging protection scheme after fast charging (24W)" He explained. After analyzing the charging management scheme, they found that Samsung used the dual core parallel charging management scheme, but its structure was different from that of Ti, which is commonly used in the industry. The "dual core" structure of Ti uses the same input current control switch, and the same entrance comes in. The current is distributed to two chips, and then combined into one after entering the battery. The two are used together. In addition, the two are in the same control loop, and the master chip stops working, and the slave chip also stops. However, this is not the case with Samsung Note7. Its main charging management chip and its slave charging management chip (from two different suppliers m and D) are independent of each other, and both are under the control of AP. Therefore, once the AP is locked, the charging management chip can not be controlled in real time. In some abnormal cases, such as the battery temperature is too high, it will cause accidents. It is precisely because the combination of low probability accidents will lead to the explosion accident, which is consistent with why it is difficult to find the hidden trouble in the R & D and trial production stage. So, Samsung's accident is not just a battery cell problem.

The most terrible thing is that if multiple risk factors exist at the same time, the probability of accidents will be large. Therefore, Ti and Saiwei both proposed that "the battery management scheme should be made into a closed-loop loop."

The so-called closed-loop loop refers to the "closed-loop battery monitoring + charging management loop, that is, the front-end of the battery meter or battery simulation monitors the battery, and the feedback information controls the behavior of the charging management IC." The charging voltage and current that the battery can bear under different conditions are different. If the temperature is high, the current should be decreased a little; if the voltage or temperature of the battery rises rapidly in a short time, it indicates that there is a big problem, and the charging management IC must stop charging immediately. The core of this technical route is to control the charging behavior through the real-time monitoring of the battery by the coulometer.

It should be noted that the monitoring and calibration methods of Saiwei and Ti battery meters are completely different (the following will analyze why the Ti battery meter causes the iPhone 6S to suddenly power down and shut down). "Saiwei's electricity meter monitors the change of internal resistance and temperature in real time, so our new battery charging management IC is based on our real-time monitoring of battery power. This forms a closed loop to control the charging behavior of the battery, which is more advantageous than using the products of two different companies." Jiang Yanbo said. It is the most close to the battery monitoring and the most accurate monitoring when the electricity meter is placed in the battery pack. Such a scheme will become more and more popular in the future.

 

Will Apple use radical high-power fast charging?

So far, apple is still using the 5V 2.4a charging, not the radical high-power fast charging? Why? Will it be adopted in the future?

Many people in the industry still remember the lesson of blood in laptops about 10 years ago, when Sony's laptops were recalled on a large scale due to a battery accident. Later, because of this incident, the standard of "secondary protection" appeared in the protection IC industry: in addition to the first level of overcharge, over-current and short-circuit protection IC, a protection IC was added at the back to prevent the secondary protection IC from starting when the first level failed. A lot of laptops are used.

But now, of all mobile phones, only apple has secondary battery protection. "However, the biggest problem with secondary protection is that fast charging is very difficult." Jiang Yanbo explained that the internal resistance of the charge discharge circuit was increased because the two protection IC circuits were connected in the charging and discharging circuit. Now when doing fast charging, people are very "concerned" about the internal resistance of the charging and discharging circuit. For example, oppo has to "calculate how to save" every milliohm internal resistance of the charging and discharging circuit. Because each milliohm will represent new heating, oppo can finally make a very small internal resistance of the charging circuit. For example, three years ago, the internal resistance of ordinary battery pack was 100 milliohm, while oppo could achieve less than 20 milliohm. Oppo has spent a lot of investment in doing this, so to speak, spare no effort. "Not only should the internal resistance of the cell be small, but also the internal resistance of the battery protection board." He explained.

This is why Apple can't achieve "fast charging" after adopting "dual protection IC". At present, it is still 5V 2.4a, which is the limit of the existing technology. Considering the battery incident caused by Samsung's radical fast charging this year, Apple will be more cautious in fast charging in the future. Chang Xu analyzes this is one of the reasons why Apple will push wireless charging next year. There are two official account for quick charging: first, fast charging, and two charging whenever and wherever possible, such as wireless charging in public places (Chang Xu recently wrote an article about the trend of next generation iPhone wireless charging and wireless charging technology, and also published in the "front edge" of electronic industry, welcome to read).

 

Recognition of the meter again after iphone6s shutdown event

It can be said that the big news of 2016 almost focused on the battery. However, the sudden shutdown of the iPhone 6S at the end of the year was also caused by poor battery management.

"It's really something to do with the meter, and there was a similar problem with the previous iPhone 6." Jiang Yanbo said. He explained that according to the discharge curve at low temperature and zero degree, TI's electricity meter may suddenly jump from 10% (or 30%, or even 50%) to 0% and shut down. Analysis reasons: first, the compensation speed of TI's power calculation method is relatively slow in temperature compensation algorithm; second, TI's power calculation method has cumulative error, which needs users to eliminate with a special scenario: no charge, no discharge, 45 minutes shutdown. In the past, when the user shut down every day, there was no problem, but now the user rarely shut down. Therefore, the calibration conditions that Ti relies on always do not appear, which will lead to the loss of long-term accuracy. That's why some people suddenly shut down at 50%, 30% and 10%, which is related to its calibration mechanism.

Why didn't this happen in the iPhone 4 / 5, but began to appear in the iPhone 6? In the past, the battery capacity of the mobile phone was sufficient compared with the power consumption ratio, which we call the multiplier. The former rate was low and the rate was low. For the electricity meter, the battery standard and calculation will be easier, and the tracking will be easier. Now the rate is higher, the problem is easy to expose.

"Since we entered the market late, and we can't do it according to TI's working principle and implementation mode, we have to find a new way, so Saiwei has adopted different algorithms and applied for our own patent. Our algorithm fastcali is constantly tracking and calibrating without shutting down. It's because we used this way when we started designing, and now it just caters to the habit of using your mobile phone without turning it off. " He said.

However, after Samsung's problems, Apple will be very conservative in battery management, so even if the above bugs appear, he should not easily replace the battery meter chip manufacturer.

"Battery meter IC has a very high threshold. In addition to being familiar with IC semiconductor technology, we also need to understand battery electrochemistry. Ti acquired battery electrochemical technology through the acquisition of benchmarq. Therefore, we invited some talent experts from BYD and ATL at the beginning. Unlike some other start-up companies, we started from scratch, so it took four years from the company's establishment to the first battery meter chip Jiang Yanbo said. Jiang Yanbo and the main members of the founding team are from Italy France semiconductor and Xinsi technology.

In Taiwan, there have been some products that copy Ti meters before, but they can't be sold on a large scale in the market due to patent problems (Ti has a very large patent pool related to coulometer patents, and its core patents are all around internal resistance tracking, tracking the battery capacity throughout the battery life cycle.) "Our 'fastcali' is totally different from TI's patents. It is totally different from TI's in terms of acquisition system and does not conflict with Ti at all." He said that Saiwei electronics had delivered 40 KK meters this year and had never received any patent lawsuits.

It should be explained here that there is a rough power calculation for the main platforms of mobile phones, such as MTK and Qualcomm. However, such a power estimation method often brings bad user experience and leads to customer complaints. With the improvement of the user experience requirements of the battery, more and more manufacturers choose the special electricity meter IC to improve the user experience, and solve many problems such as the drastic change of the battery discharge capacity in the full temperature scene, and the capacity attenuation in the whole life cycle of the battery.. Moreover, as mentioned above, with the development of fast charging to higher power, the accurate and close to the battery independent meter IC becomes very important. A "closed loop battery monitoring + charging management loop: that is, the electricity meter monitors the battery, and the feedback information controls the behavior of the charging management IC." Very important.

Jiang Yanbo: the calibration mechanism of our electricity meter is completely different from that of Ti. Our algorithm fastcali is to continuously track and calibrate without shutting down.

128 bit encryption for "fake battery" management

Battery authentication chip is also a necessary chip in the era of fast charging, because the battery is absolutely not allowed to be "fake" after fast charging. Now that the charging rate has reached 1C or 2c, it must be customized by the mobile phone manufacturer and cell manufacturer to withstand such a large current. If it is a third-party battery (such as being replaced during maintenance), there will be a potential safety accident after replacement. Therefore, an authentication chip integrated with AES 128 bit algorithm is needed to authenticate the authenticity of the battery by authenticating with the application processor of the mobile phone. In addition, in order to prevent the maintenance shop from "replacing the battery core without replacing the circuit board", the authentication chip should be designed so that as long as the power supply fails, the AES algorithm will be destroyed and the battery will not work. "This chip Saiwei is also ready to launch next year." Jiang Yanbo revealed.

"In the future, the function of battery pack will be more and more perfect and more complex." To the real "smart battery" direction. Battery authentication oppo is now in use, which is ti's solution. Huawei mate9 uses a custom chip in its battery pack. It is speculated that the authentication algorithm is also used. However, it is very difficult for Huawei to customize the IC, and most companies can't do it themselves. Hisilicon also has its own charging management chip. "Every company has its own practice. The advantage of our charging authentication IC is that the power consumption is very low, only 3 μ a, which does not constitute a load on the battery." He said.

How does the power bank identify various fast charging mobile phones?

Now the power bank is also developing to the fast charging function, but how can it identify the various technical schools of complexity? "Now we are in a stage of standard confusion. Is MTK pe3.0 through or high pass QC3 or type C? Recently, when the qc4.0 of Qualcomm is compatible with typec, the standard will be relatively simplified. In the future, everyone in the physical layer will use typec uniformly, and the upper layer will run their own commands. Therefore, only the 5V 3a of typec should be compatible. However, for mobile power supply, the two modes are still difficult to be compatible: direct charging is to reduce voltage, and other fast charging standards are to boost voltage. " Jiang Yanbo explained, "in the future, we will do intelligent USB fast charging recognition, with built-in MCU and algorithm, which can identify each fast charging scheme." Anker, the largest USB power supplier in North America, is one of Saiwei's major customers.

In addition, more and more notebook computers can also fast charge mobile phones (5V, 2.4 / 2a): when the notebook computer is turned on, because of the communication function, it is 1.5A to charge the mobile phone; when the laptop is off / standby, it can charge the mobile phone 5V 2.4a/2a quickly. "In the field of USB fast charging identification, we are trying to add additional value. For example, we have added the current limiting protection of the USB port, and now the type C identification chip has added the port current limiting switch, and more communication functions will be added later." He said. He pointed out that when some laptops use this function, they need to set it in BIOS, especially the power off charging function, which is not the default function.

In addition to the power bank, car charging, wall plug, row plug, etc. need to use fast charging identification to charge different mobile phones.

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