Introduction of Li-ion Battery Management Chip

　　A brief introduction to the application of lithium-ion battery management chips and its low-power design for readers to further understand the relevant knowledge of this type of battery management chips.

　　1.1 The application and development of lithium-ion battery management chips 1.1.1 The characteristics and applications of lithium-ion batteries The rechargeable lithium battery is only used in the commercial field for the first time. In the 1980s, the focus of research was on rechargeable lithium-ion batteries (Li-ionBattery), but it did not successfully solve the battery safety problem. Until 1991, Sony realized the commercialization of lithium-ion batteries for the first time, which was regarded as an important milestone in the field of energy technology. As shown in Table 1.1, compared with other secondary batteries such as Ni-Cd, lithium-ion batteries have higher energy density (including mass specific energy and volume specific energy), higher charge and discharge cycles, and lower discharge rate. And higher working voltage of single cell battery (3.6V). Obviously, the high working voltage of the lithium-ion battery will help reduce the size of mobile equipment, the high energy density will help the weight of the battery, and the low discharge rate can also ensure normal use during storage.

　　Over the past ten years, the application of lithium-ion batteries has developed tremendously and has now become one of the main energy sources for communication electronic products. It is widely used in high-end portable consumer products such as notebook computers, GSM/CDMA, digital cameras, camcorders, and PDAs. In electronic products [2]. If adapting to the notebook computer market, reducing battery costs, and increasing capacity before 1997 are called the first golden age of lithium-ion batteries, the popularization of portable electronic products such as mobile phones and video cameras will enable the lithium-ion battery industry to enter the second golden age. . For example, in 2004, 94% of mobile phone batteries were lithium-ion batteries. With the development of technology, the demand for lithium-ion batteries will become increasingly strong, and it is expected to reach 1.2 billion in 2005 [3]. From the perspective of the production and sales distribution of lithium-ion batteries, Japan was the largest producer and sales country of lithium-ion batteries before 2000, with a market share of more than 95%. However, with the rapid rise of China and South Korea in recent years, Japan's unique pattern has been gradually broken. It is expected that the global market share of lithium-ion batteries in Japan will fall below 50% in 2005.　　The importance of 1.1.2 lithium-ion battery management chip　　In the research and development of lithium-ion batteries, improving the safety of use has always been the focus of research. Since the mass ratio is high and the electrolyte is mostly organic combustibles, when the battery heat generation rate is greater than the heat dissipation rate, safety problems may occur. Studies have pointed out that when a lithium-ion battery is abused, it may reach a high temperature above 700°C, which may cause the battery to smoke, catch fire or even explode; when the over-discharge is lower than 1V, copper will precipitate on the surface of the positive electrode, causing the inside of the battery Short circuit; in the case of overcurrent, the internal temperature of the battery is also very easy to rise, which will deteriorate or even damage the battery performance. Figure 1.1.1 shows the chemical reactions and performance changes inside lithium-ion batteries under overcharge and overdischarge conditions, where M represents Co, Al, Ni and other metal ions.

　　To improve the safety of lithium-ion batteries, in addition to in-depth mechanism research, selection of appropriate electrode materials and optimization of the overall structure, the battery must also be effectively managed by the integrated circuit (IC) around the battery. It is reported that in recent years, battery management (BatteryManagement) chips, both in terms of sales and sales, are expected to grow the fastest in power management (PowerManagement) chips. Li-ion battery management objectives include battery voltage monitoring, charge and discharge current monitoring, temperature monitoring, data calculation and storage. The management chip, including the protection circuit, the fuel detection circuit, and the system capable of carrying out battery data transmission, is called the Smart Battery System (SBS). The structure of the SBS battery pack is shown in Figure 1.1.2. It is protected by a temperature sensor, a current detector capable of detecting bidirectional current, ADC, EEPROM memory, clock, status/control circuit, single-wire interface and address with the main system, and lithium-ion battery protection Circuit and other components. Among them, the digital quantity converted by ADC is stored in the corresponding memory, which is connected with the main system through a single-wire interface, and read/write access and control of the internal memory are performed. In addition to effectively protecting the battery, SBS can also output the remaining battery energy signal (displayed by LCD), which will be the main goal of the development of lithium-ion battery management chips. At present, the SBS application protocol has developed to SBdata1.1 (data protocol) and SMbus2.0 (bus protocol). In notebook computers such as IBM and Sony, several models have adopted SBS based on battery protection circuits. 　　In the ion battery management chip, because the protection circuit can monitor the battery voltage and charge and discharge current, it can be built into the lithium ion battery alone or used as a secondary protection circuit in the SBS. What's more, it can It achieves the same protection for Ni-Cd and Ni-H batteries, so it occupies a large share of battery management chips.　　1.1.3 Development status of battery management chips　　At present, foreign companies such as Unitrode, Texas, Dallas, etc. have carried out research and development on lithium-ion battery management chips. Unlike the declining share of battery production in the global market, Japan’s lithium-ion battery management chips, especially the design and development of protection circuits, have always occupied a leading position in the world. The most famous products are Seiko's S82 series, Ricoh's R54 series and MITSUMI's MM3061 series. Among them, the S82 series of products are considered to be one of the leaders in the design of lithium-ion battery management chips because of their complete functions, high accuracy and low power consumption. In China, in addition to individual units in Taiwan that have developed protection chips with relatively simple functions, in recent years, although individual units in mainland China have begun to study lithium-ion battery protection circuits, they are all in their infancy, with low accuracy and no unified protection. standard. More importantly, there is currently no circuit with independent property rights in China.　　 At present, in order to strike a balance between the longest battery life and the lightest weight, more and more portable devices such as mobile phones and video cameras use single-cell lithium-ion batteries as their main power source. The current research on management chips for single-cell lithium-ion batteries focuses on: 　　① In addition to effective management of the battery charging process, there is also an urgent need to realize the full protection of the charging and use process. This requires that the chip not only has a complete protection function, but also the protection accuracy such as battery voltage and delay time detection and control accuracy meet practical requirements.　　②The power consumption should be reduced as much as possible to extend the service life of the power supply battery. As part of the packaged battery, the drive of the chip always comes from the managed battery, so the chip is required to have sufficiently low current consumption.　　 As a digital-analog mixed-signal circuit, some existing power optimization methods can be used for reference, but combining application characteristics to reduce power consumption requires more in-depth theoretical exploration. Therefore, research on the low power consumption of battery management chips represented by single-cell lithium-ion protection circuits, from the realization of system functions to the low-power design of digital-analog mixed signal circuits, the design of battery management chips and even the development of SBS Quite a reference.　　1.2 Low-power design for digital-analog mixed-signal circuits　　1.2.1 Low-power design motivation for integrated circuits　　In the early days of integrated circuit development to the 1980s, the power consumption problem was not very prominent. During this period of time, due to the generally small scale of circuit systems and the rise of CMOS technology, low power consumption has not yet been regarded as an important factor in IC design.　　 In 1968, G. Moore, one of the founders of Intel, predicted that every 18 to 24 months, the integration level of IC will double. This is the famous Moore's law. In fact, over the past forty years, IC technology has basically followed Moore's law and has achieved tremendous development. Integrated circuits have evolved from small-scale integration (SSI) to very large-scale (VLSI) to the current very large-scale integration (ULSI), that is, a chip can contain more than 100 million components. Although quantum effects and economic constraints will slow down the growth of IC integration, it is foreseeable that the momentum of continuous development of IC integration will not change with the adoption of new technologies. At the same time, the complexity of the system is constantly improving, that is, devices and circuits with different functions are integrated on a chip to form a system integrated chip (SOC). Obviously, the increase in the complexity and integration of integrated circuits makes low power consumption an indispensable circuit design indicator.　　 First of all, excessive power consumption will make the chip easy to overheat, reduce the reliability of the circuit, and eventually lead to failure. Studies have shown that for every 10C increase in temperature, the failure rate of the device will double; in addition, the ever-increasing power consumption will put forward higher requirements for the packaging and heat dissipation of the chip, which will not only increase the cost, but also in the miniaturization In applications, this scheme is often not adopted.　　 More importantly, the development of consumer electronics and a large number of applications have promoted the research on power consumption. The concept of low power consumption was first proposed by industries such as electronic watches, and in miniaturized, highly integrated consumer electronic products, in order to reduce circuit costs, improve circuit stability, and reliability, it is more necessary to design low-power circuits , To ensure that when the integration level increases, the unit area maintains the same or even lower power consumption. At the same time, because the battery capacity has only increased by 2 to 4 times in the past thirty years, it is far from the rapid development of VLSI technology, so in battery-powered systems, the low-power design of integrated circuits is the most important way to extend battery life. Effective means. In addition, portable devices tend to use fewer batteries to reduce size and weight, which inevitably require circuits to achieve low power consumption. Compared with ten years ago, the proportion of consumer electronics in the electronics industry has grown rapidly from 40% to 55%. Therefore, it can be said that consumer electronics are the main driving force for low-power design.　　1.2.2 Low-power research of digital-analog mixed-signal circuit　　Under the strong promotion of this technical demand and the application demand of portable electronic products, the low-voltage and low-power design of CMOS integrated circuits has received great attention. At present, people's research on the power consumption of integrated circuits is mainly concentrated in the following two aspects: 　　 One is the research on low power consumption technology. This is mainly focused on reducing the feature size, lowering the power supply voltage and lowering the threshold voltage. Reducing the feature size helps to integrate complex systems on the same chip for effective power management. But when the feature size is reduced to a certain extent, the hot carrier effect and the soft failure of the dynamic node will greatly affect the performance of the device, and reducing the power supply voltage becomes a better solution to the above problems. In order to ensure that the drive current of the low-voltage logic circuit does not decrease and the operating frequency does not decrease, it is required to reduce the threshold voltage while reducing the power supply voltage. However, reducing the threshold voltage in the same proportion will increase the leakage current exponentially. The use of multi-threshold voltage devices or the use of variable threshold voltage technology is expected to reduce the power consumption caused by the leakage current, and these technologies are more dependent on the manufacturing process.　　 The second is the study of low-power design methods. This is currently the most active area in low-power research. In the case of process determination, it includes low-power design methods and evaluation methods, but mainly for digital circuits.　　Under the premise of ensuring the same performance of the system, in the early stage of chip design, power consumption is analyzed and optimized from various levels, which can not only shorten the design cycle, but also achieve the goal of minimizing overall power consumption. From a design perspective, low-power design methods can be divided into system level (SystemLevel), algorithm/structure (Architecture/AlgorithmLevel), register transfer level (RegisterTransferLevel, RTL), logic/gate level (LogIC/GateLevel), layout level (LayoutLevel) ) These levels. Among them, the system and algorithm, as a high-level low-power technology, has a great impact on system power consumption. Power consumption analysis at this level will be able to predict and optimize the system power consumption, and can achieve several orders of magnitude power consumption reduction, so we must pay attention to it.　　Effective power consumption assessment tools and methods are another important content of low power consumption research. How to quickly and accurately estimate circuit power consumption at different levels of design is also a hot and difficult issue in integrated circuit design. Generally, the power consumption assessment is divided into two categories based on random statistics and simulation methods.　　 The power consumption estimation method based on random statistics, the basic idea is: first extract the circuit or logic model according to the layout or logic description of the module, and then simulate with the randomly generated input stream to calculate the average power consumption.　　 Its advantage is that it is faster and does not require internal information of the circuit, but the power consumption estimation is not as accurate as the simulation-based method, so it is suitable for the early stages of the usual design.　　 The simulation-based power consumption estimation method is to simulate power consumption with a set of typical input vectors to obtain the average power consumption, maximum power consumption and minimum power consumption values. Simulation-based methods have high accuracy, but occupy a large storage space and simulation time, so some heuristic information can be used to accelerate convergence, such as Monte Carlo simulation methods and genetic algorithms. Among them, the Monte Carlo method is to randomly generate an input signal at the input of the circuit, and then use an analog method to calculate the power consumption in a certain time interval. If the existing circuit-level and gate-level simulation methods are used in the inner loop of the Monte Carlo program, it will be possible to achieve a compromise between speed and calculation accuracy. Typical power analysis software based on simulation methods include POWERMILL, Entice-Aspen, etc.　　 It needs to be pointed out that most of the current low-power research is to discuss analog and digital circuits separately. This is closely related to the characteristics of the analog circuit itself. The analog integrated circuit is different from the digital circuit that processes 0 or 1 signals. It mainly processes signals with continuous changes in amplitude, time, and frequency, and has the following characteristics: 　　①Diversity of circuit forms. Including data converters (such as A/D converters, D/A converters, etc.), operational amplifiers, linear amplifiers (low noise amplifiers, broadband amplifiers, etc.), nonlinear amplifiers (analog multipliers, logarithmic/antilog amplifiers, etc.) ), multiple analog switches, power supply voltage regulators (linear voltage regulators, switching power supply controllers, etc.), smart power ICs and various special ICs. 　　②Diversity of performance indicators. Including accuracy, input range, distortion, noise, power supply voltage rejection ratio (PSRR), gain, frequency bandwidth, input/output impedance, etc.　　③Diversity of circuit structure. Taking just one op amp as an example, there are many structures such as two-stage, Cascode, folded (Folded) Cascode, Class A/AB amplifier, single-ended/differential amplifier and so on.　　④The variety of devices. Common devices include transistors, diodes, resistors, capacitors, and even inductors.　　Analog circuit processing signal continuity, circuit structure form