Lithium-ion battery management chip application and its low power design

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1.1 Application and development of lithium ion battery management chip

1.1.1 Characteristics and application of lithium ion battery

As early as 1912, the study of lithium batteries (Li Battery) with lithium metal as the electrode began. In the 1970s, non-rechargeable lithium batteries were first used in the commercial field. In the 1980s, research focused on rechargeable lithium-ion batteries (Li-ion Battery), but did not successfully solve the battery safety problem. Until 1991, Sony first realized the commercialization of lithium-ion batteries, which is considered to be an important milestone in the field of energy technology.

As shown in Table 1.1, lithium ion batteries have higher energy density (including mass ratio energy and volume ratio energy), higher charge and discharge cycles, and lower discharge rate than other secondary batteries such as Ni-Cd. And higher single cell operating voltage (3.6V). Obviously, the high operating voltage of the lithium-ion battery will help to reduce the size of the mobile equipment. The high energy density will help the battery to be lightweight, and the low discharge rate will ensure normal use during storage.

In the past ten years, the application of lithium-ion batteries has been greatly developed, and it has 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 it is the first golden age for lithium-ion batteries to adapt to the notebook market before 1997, reduce battery costs and increase capacity, then the popularity of portable electronic products such as mobile phones and video cameras will bring the lithium-ion battery industry into 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, with an estimated 1.2 billion in 2005 [3]. From the perspective of the production and sales distribution of lithium-ion batteries, before 2000, Japan was the largest producer and seller of lithium-ion batteries, with a market share of over 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.

1.1.2 Importance of Lithium Ion Battery Management Chips

In the research and development of lithium-ion batteries, the issue of improving the safety of use has been the focus of research. Since the mass ratio energy is high, and the electrolyte is mostly organic flammable materials, when the heat generation rate of the battery is greater than the heat dissipation speed, safety problems may occur. Studies have pointed out that lithium-ion batteries may reach temperatures above 700 °C when they are abused, causing the battery to emit smoke, fire and even explosion. When over-discharged below 1V, copper will be deposited 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 extremely easy to rise, which deteriorates or even damages the battery performance. Figure 1.1.1 shows the chemical reaction and performance changes in the lithium ion battery under overcharge and overdischarge conditions, where M represents metal ions such as Co, Al, and Ni.

In order to improve the safety of lithium-ion battery use, in addition to conducting in-depth mechanism research, selecting appropriate electrode materials and optimizing the overall structure, the battery must be effectively managed by an integrated circuit (IC) on the periphery of the battery. It has been reported that in recent years, battery management chips, both in terms of sales and sales, are expected to grow fastest in power management chips. Lithium-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 performing battery data transmission, is called a Smart Battery System (SBS). The structure of SBS battery pack is shown in Figure 1.1.2. It consists of temperature sensor, current detector capable of detecting bidirectional current, ADC, EEPROM memory, clock, status/control circuit, single line interface and address with main system, and protection of lithium ion battery. Circuit and other components. The digital quantity converted by the ADC is stored in the corresponding memory, and is connected to the main system through a single-wire interface to perform read/write access and control of the internal memory. In addition to effectively protecting the battery, SBS can also output the remaining energy signal of the battery (displayed by LCD), which will be the main goal of the development of lithium-ion battery management chip. Currently, SBS application protocols have evolved to SBdata 1.1 (data protocol) and SMbus 2.0 (bus protocol), while in IBM and Sony notebooks, several models have adopted SBS based on battery protection circuits.

In the lithium ion battery management chip, the protection circuit can realize the monitoring of the battery voltage and the charging and discharging current, and can be separately built in the lithium ion battery, and can also be used as the secondary protection circuit in the SBS, and more valuable, It can achieve the same protection for Ni-Cd and Ni-H batteries, so it accounts for a large share of battery management chips.

1.1.3 Development Status of Battery Management Chips

At present, foreign companies such as Unitrode, Texas, and Dallas have carried out research and development on lithium-ion battery management chips. Different from the continuous decline in battery production in the global market, Japan's lithium-ion battery management chips, especially the design and development of protection circuits, have always dominated the world. The most famous products are Seiko's S82 series, Ricoh's R54 series and MITSUMI's MM3061 series. Among them, S82 series products are considered to be one of the leaders in the design of lithium-ion battery management chips because of their complete functions, high precision and low power consumption. In China, in addition to some Taiwanese units that have developed relatively simple protection chips, in recent years, although some mainland units have begun to study lithium-ion battery protection circuits, they are all in their infancy, with low precision and no uniform protection. standard. More importantly, there are no circuits 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 a single-cell lithium-ion battery as the main power source. At present, research on management chips for single-cell lithium-ion batteries focuses on:

1 In addition to effective management of the battery charging process, it is more urgent to achieve full protection of the charging and use process. This requires the chip not only has a complete protection function, but also the protection accuracy such as battery voltage, delay time detection and control accuracy meet practical requirements.

2 Power consumption should be reduced as much as possible to extend the 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 a sufficiently low current consumption.

As a digital-analog mixed-signal circuit, we can learn from some existing power-optimization methods, but combined with the application characteristics to reduce power consumption, we need to conduct more in-depth theoretical exploration.

Therefore, the low power consumption of the battery management chip represented by the single-cell lithium-ion protection circuit is studied. From the realization of the system function to the low-power design of the digital-analog mixed-signal circuit, the design of the battery management chip and even the development of SBS will be Quite a reference.

1.2 Low-power design of digital-analog mixed-signal circuit

1.2.1 Low-power design drivers for integrated circuits

In the early days of integrated circuit development, the power consumption problem was not very prominent in the 1980s. During this time, due to the generally small size of the circuit system and the rise of CMOS technology, low power consumption has not been used as an important factor in IC design.

In 1968, G. Moore, one of Intel's founders, predicted that IC integration would double every 18 to 24 months. This is the famous Moore's Law. In fact, for more than 40 years, IC technology has basically followed the development of Moore's law. Integrated circuits have evolved from small-scale integration (SSI) to very large-scale (VLSI) to today's very large-scale integration (ULSI), a level that can contain more than 100 million components on a single chip. While quantum effects and economic constraints will slow the growth of IC integration, it is foreseeable that the momentum of continued integration of IC adoption with new technologies will not change. At the same time, the complexity of the system is constantly improving, that is, the devices and circuits of different functions are integrated on one chip to form a system integrated chip (SOC). Clearly, the complexity and integration of integrated circuits has made low power consumption an indispensable circuit design indicator.

First, excessive power consumption will make the chip susceptible to overheating, circuit reliability will drop, and eventually lead to failure. Studies have shown that for every 10 C increase in temperature, the device's failure rate will be doubled. In addition, the increasing power consumption will put higher requirements on the package and heat dissipation of the chip, which will not only increase the cost, but also be small. In applications, such solutions are often not adopted.

More importantly, the development and mass application of consumer electronics has driven research into power consumption issues.

The concept of low power consumption was first proposed by the industry such as electronic watches. In the miniaturized and highly integrated consumer electronics products, in order to reduce circuit cost, improve circuit stability and reliability, it is necessary to design low-power circuits. To ensure that the unit area maintains the same or even lower power consumption as the level of integration increases. At the same time, because the capacity of the battery has only increased by 2 to 4 times in the past three decades, far from the rapid development of VLSI technology, in the battery-powered system, the low-power design of the integrated circuit is the most prolonged battery life. Effective means. In addition, portable devices tend to use fewer batteries to reduce size and weight, and also require circuits to achieve low power consumption. Compared with a decade ago, the proportion of consumer electronics in the electronics industry has grown rapidly from 40% to 55%, so consumer electronics can be said to be the main driver of low-power design.