The introduction of lithium-ion battery management chip

1.1Lithium ion batteries management application and development of the chip

1.1.1 The characteristics and applications of lithium ion battery

As early as 1912, the research on 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 Corporation realized the commercialization of lithium-ion batteries for the first time and was considered an important milestone in the field of energy technology.

Compared with Ni -Cd and other secondary battery, lithium ion batteries with higher energy density than energy and volume (including quality), higher charge and discharge cycle, lower the discharge rate and the higher the single battery voltage (3.6 V).Obviously, the high working voltage of the lithium ion battery will beneficial to reduce the size of the mobile equipment, high energy density will be good for the battery of lightweight, low discharge rate can also ensure the normal use of storage period.

This decade, the application of lithium ion batteries obtained tremendous development, has now become one of the major energy electronic communication products, widely used in notebook computers, GSM/CDMA, digital camera, video camera and PDA [2] in the high-end portable consumer electronics products. If 1997 years ago to adapt to the notebook PC market, reduce battery costs, increase capacity is referred to as lithium ion battery first golden period, so in the popularity of mobile phones, cameras and other portable electronic products will make the lithium ion battery industry into the second golden period. In 2004, for example, 94% of mobile phone battery is lithium ion battery. With the development of technology, the demand for lithium ion batteries will be increasingly strong, is expected in 2005, 2005 [3].From the point of the production and sales distribution of lithium ion battery, before 2000, Japan is the biggest production and lithium ion batteries are sold, the market share of 95% or more. But in recent years along with the rapid rise of China and South Korea, Japan, a country's pattern has been gradually broken, is expected in 2005 Japan's worldwide market share of lithium ion battery will fall below 50%.

1.1.2 The importance of lithium ion battery management chip

In lithium ion battery research and development, improve the use safety is always the key point of the research. Because quality is higher than the energy, and most of the organic electrolyte tinder, etc., when the battery heat generated when the speed is greater than the cooling speed, it is possible to security problems. Studies have pointed out that the lithium ion battery at the abuse, could reach above 700 ° C high temperature, which leads to batteries in smoke, fire and explosion; When discharge to below 1 v, will precipitate copper anode surface, cause the battery internal short circuit; In flow conditions, the battery internal temperature to rise, make a battery performance deterioration and damage. Under the overcharge and discharge conditions, the chemical reaction and performance of the lithium ion battery internal changes, type of M represents Co, Al, Ni and other metal ions.

To improve the safety of the lithium ion battery, in addition to the mechanism of in-depth research, choose suitable electrode material and optimization of the overall structure, also must through the battery of peripheral integrated circuit (IC) of battery for effective management. There have been reports in recent years, the battery management (Battery Management) chip, whether in sales or sales management (Power Management) power consumption is expected to grow the fastest in the chip. Lithium ion battery management goals include the battery voltage, charge and discharge current, temperature monitoring, data computing and storage. Management chip, including protection circuit, fuel cells detection circuit and the ability to implement data transmission system is referred to as smart battery system (Smart Battery System, SBS).SBS battery structure consists of temperature sensors, to detect the bidirectional current block current detector, ADC, EEPROM memory, clock, single state/control circuit, and the main system interface and address, lithium ion battery protection circuit, etc. By the ADC conversion of digital storage within the corresponding memory, through a single interface connected to the main system, the internal memory read/write access and control.SBS besides to effectively protect the battery, battery remaining power output can also signal (LCD display) are available, and this will be the main goal of the lithium ion battery management chip development. At present, the application of the SBS agreement reached SBdata1.1 (data protocol) and SMbus2.0 (bus protocol), and such as IBM and SONY laptop, there are several models have been adopted based on the battery protection circuit of SBS.

In lithium ion battery management chip, the protection circuit due to the battery voltage, charge and discharge current monitoring can be accomplished, it can separate built-in lithium ion battery, can also act as a secondary protection circuit in the SBS with, the more valuable is that it can realize the Ni - Cd, Ni - H equal protection of the battery, so in battery management chip accounted for a large share.

1.1.3 Battery management chip development present situation

At present, foreign unitrode, Texas, Dallas and other companies have carried out research and development of lithium ion battery management chip. And battery production in the global market share declining, Japanese lithium ion battery management chip, especially the protection circuit design and development, has always been in a dominant position in the world. Is the most famous products seiko S82 series, ricoh R54 series and MITSUMI MM3061 series, etc. Among them, the S82 series products because of complete functions, high precision and low power consumption, is considered to be one of lithium ion battery management chip design leader. In China, besides the function of individual units of Taiwan has developed a relatively simple protection chip, in recent years, although there are individual mainland began to research on lithium ion battery protection circuit unit, but is in its infancy, low precision and no unified standard of protection. More important is, at present the domestic haven't circuit with independent property rights to.

At present, in the longest battery in order to strike a balance between time and the lightest weight, a growing number of portable devices such as mobile phones, cameras are using single section of lithium ion battery as the main power supply. Current research single section of the lithium ion battery management chip, the emphasis is on:

(1) In addition to the battery charging process for effective management, also more urgently need to implement in the whole process of the process of charging and use protection. This requires a chip not only has perfect protection function, and to protect such as battery voltage, delay time precision of detection and control precision to meet the practical requirements.

(2) It should be as much as possible to reduce power consumption to extend the service life of power battery. As part of the package after the battery, the chip driver always from the management of the battery, so the chip should have enough low current consumption.

As a d/a mixed signal circuit, can draw lessons from the existing some power consumption optimization method, but combining with the characteristics of application of reducing power consumption, to conduct more in-depth theoretical exploration.

So the represented by single section lithium protection circuit of the battery management chip, low power consumption, from the system function realization to analog mixed signal circuit design, low power consumption of the battery management chip design and even the development of SBS will have considerable reference.

The low power design of 1.2 d/a mixed signal circuit

1.2.1Low power design of integrated circuit

In the early stages of the development of integrated circuits to the 1980 s, power dissipation problem is not very prominent. During this period, due to the generally small scale and the rise of a CMOS circuit system, low power consumption has not been as an important factor of IC design.

In 1968, one of the founders of Intel G.Moore forecast, every 18 to 24 months, IC integration will double, and this is the famous Moore's law. In fact, these forty years, IC technology is basically follows the Moore's law has achieved great development. Integrated circuit has experienced the development 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 one hundred million elements. Although quantum effects and economic limit will make IC integration slowing in the rate of growth, but predictably, with the adoption of new technology of IC integration of sustainable development trend will not change. At the same time, the complexity of the system is also constantly improving, the different functions of devices and circuits are integrated into a chip, chip (SOC) constitute a system integration. Obviously, the improvement of integrated circuit complexity and integration makes the circuit design of low power consumption is becoming an indispensable index.

First of all, high power consumption will make the chip easy to overheat, circuit reliability, eventually lead to failure. Studies have shown that the temperature rise every 10 c, twice will improve the failure rate of the device; In addition, the increasing power consumption will give chip encapsulation and cooling put forward higher request, this will not only increase the cost, but also in the miniaturization of applications, this solution are often not be adopted.

More importantly, consumer electronics and a large number of applications to promote the development of the research to the problem of power consumption.

Is the concept of low power consumption by electronic watches and other industries for the first time, and in consumer electronics miniaturization, high integration, in order to reduce the circuit cost, improve the stability, reliability, more need to design low power circuit, to ensure that when the integration to improve, to maintain the same or even lower power consumption per unit area. At the same time, because in the past 30 years of battery capacity increased 2 ~ 4 times, only far from VLSI technology has developed rapidly, so the battery power supply system, the low power design of integrated circuit is the most effective way to prolong the service life of the battery. In addition, portable devices tend to use less of the battery, to reduce the size and weight, also inevitable requirement circuit to implement low power consumption. Compared with a decade ago, consumer electronic products in the electronics industry has been rapid growth from 40% to 40%, therefore consumer electronics is the main driver of low power design.

1.2.2, d/a mixed signal circuit of low power consumption research

In this technical requirements and the application of portable electronic products demand strong, driven by low voltage low power CMOS integrated circuit design has received great attention. At present, the power consumption of integrated circuit research, mainly concentrated in the following two aspects:

First is the study of the low power technology. This is mainly concentrated in the reduced feature sizes, to reduce the supply voltage and threshold voltage reduction. To decrease the size of characteristics, conduce to complex system integration on the same chip, effectively managing power consumption. But when the feature sizes down to a certain degree, the hot carrier effect, soft dynamic node failure will greatly affect the performance of the device, reduces the power supply voltage become better solutions to solve these problems. Low logic circuit in order to keep the drive current don't reduce and working frequency is reduced, to reduce the supply voltage as well as to reduce the threshold voltage, but with the lower threshold voltage can make the leakage current increases exponentially. USES the threshold voltage devices or USES the variable threshold voltage technology is expected to reduce the power dissipation caused by leakage current, which are dependent on manufacturing process.

The second is low power design methods of research. This is the low power consumption are the most active in the study area. Technology in certain circumstances, it is including low power design methods and evaluation methods, but they are mainly for digital circuit.

On the premise of guarantee the same performance, at the beginning of the chip design, from all levels to analyze power consumption optimization, not only can shorten the design cycle, also be able to achieve the overall power consumption minimization. From the perspective of design, low power design methods can be divided into system level (System Level), the algorithm/structure (Architecture/Algorithm Level), register transfer level (RTL Register Transfer Level,), logical/levels door (LogIC/Gate Level), landscape (Layout Level) these levels. Among them, the system and the algorithm for low power technology in the high level, will affect the power consumption of the system. At this level of power consumption will be able to forecast the power consumption of the system analysis and optimization, which can be several orders of magnitude lower power consumption, so must be attention.

Effective assessment tools and power consumption method is another important part of the study of low power consumption. How to design different levels to rapidly and accurately estimate the power consumption of the circuit, is also a hot and difficult problem in the design of integrated circuit. In general, the power consumption of evaluation is divided into the method based on random statistical and simulation the two classes.

Based on random statistical method for estimating the power consumption, and its basic idea is: first, according to a map or logic description module extraction circuit or logical model, and then use random input flow simulation, calculate the average power consumption.

It has the advantage of fast, and there's no need to circuit inside information, but power consumption estimation accuracy than the method based on simulation, so apply to usually in the early stages of design.

Based on simulation method for estimating the power consumption is to use a set of typical input vector power simulation, in order to obtain the average power consumption, maximum power consumption and the minimum power consumption value. Based on the simulation method of high precision, but accounts for a bigger storage space and time simulation of some heuristic information can therefore be used to speed up convergence, such as monte carlo (Monte Carlo)

The simulation methods and genetic algorithms, among them, the Monte Carlo method randomly generates an input signal at the input of the circuit, and then uses an analog method to calculate the power consumption in a certain time interval. If the existing circuit level, gate level and other simulation methods are applied to the inner loop of the Monte Carlo program, a compromise between speed and calculation accuracy will be achieved. Typical power analysis software based on analog methods are POWERMILL, Entice-Aspen, and so on.

Need to point out that the current low power research mostly for analog and digital circuits are separately discussed. The analog circuit and closely related to its own characteristics analog integrated circuit and 0 or 1 signal processing of digital circuit is different, it is mainly dealing with continuous variation of signal amplitude, time, frequency, and has the following features:

Diversity in the form of (1) circuit: Including data converter (such as A/D converter, D/A converters, etc.), operational amplifier and linear amplifiers (low noise amplifier and broadband amplifier, etc.), nonlinear amplifier (analog multiplier, logarithmic/antilog amplifier, etc.), multi-channel analog switch, the power supply voltage regulator (linear voltage regulator, switching power supply controller, etc.), smart power IC and all kinds of special IC.

(2) The diversity of performance indicators: Including precision, input range, distortion, noise and power supply rejection ratio (PSRR), voltage gain, frequency bandwidth and input/out impedance, etc.

(3) The diversity of circuit structure: Only in the case of an op-amp, there are two levels, Cascode, folding, Folded Cascode, A/class AB amplifier, single-ended/differential amplifier, and many other structures.

(4) The variety of devices. Common devices are transistors, diodes, resistors, capacitors, and even inductors.

The continuity of analog signal processing circuit, the circuit structure in the form of diversity, the precision of the performance index, makes the design of circuit and layout must be built around the specific circuit, design of the automatic degree is much lower than the digital circuit, and the difficulty is far higher than the latter.

Although in the digital age, digital circuit design method, the process conditions are leading in the analog circuit, digital IC market share also higher than analog IC, but, after all, analog circuit is the bridge of digital circuit and the real world, so it still has enough space for development. In addition, in the high complexity of the actual system, always put the storage circuit, logic control circuit and analog circuit integrated together in the same chip, known as the mixed-signal circuits. CMOS technology mature and widely application in the digital circuit, also requires system analog circuit technology to be compatible with standard CMOS process, therefore, in the analog circuit including power consumption, performance will directly determine the performance of the system.

In mixed signal circuits, many successful applications in low power consumption in digital circuits technology, is not suitable for application in analog circuit. For example, an effective way to reduce the power consumption of the power supply voltage is reduced, but for analog circuit, as the literature [16] points out, for a given dynamic range, gain and gain bandwidth product, reduce the power consumption of the power supply voltage will makes higher, it also shows that in low voltage, low power consumption at the expense of the sacrifice part of the circuit performance. Because the performance of the analog circuit can't out of the specific circuit to discuss, so more literature reported low voltage low power circuit design.

As more and more batteries mixed-signal circuit, the traditional design method was given a strong challenge. Low power requirement for the mixed signal circuits for unified management, power consumption rather than isolated from analog and digital circuit. From the perspective of design, how to coordinate the power consumption of digital and analog circuit, will encounter than pure digital circuit or pure analog circuits more difficult. Mixed signal of low power consumption, therefore, the research start caused people's attention: the literature [17] in the design of laser driver, used digital signal to control current switch to reduce power consumption, but is the plus digital signal; Literature [18], [19] proposed the use of digital signal to control the analog circuit, but the purpose is to reduce the circuit noise rather than power consumption. In 2001, Tsinghua University digital circuit of signal is put forward to control the activities of the analog circuit, the so-called Pulsed - Activation in order to save the system power consumption [20], but only from the circuit to justifying the feasibility of the method, how to effectively save mixed-signal system power consumption, and no further theoretical study. Should see, the mixed signal circuit of low power consumption, will involve the hot field of low-power analog and digital design, but also has a lot of problems not solve, worthy of further deepening and perfect.

1.3 research content and structure

In order to achieve the protective function of lithium battery management chip and low power design requirements, main research content of this article are as follows: low power consumption of each part of mixed-signal circuit design and collaborative thinking method; The protective function of lithium ion battery management chip design and low power consumption; Circuit design and simulation, layout and simulation, including power consumption, later.

According to the requirements of the content, this paper studies focused on the following aspects:

Analog hybrid circuit method of low power consumption analysis: (1) research is an extensive literature low power consumption, but most are separate digital circuit and analog circuit to consider. As a practical mixed-signal system, low power design cannot be separated from system application occasions, and it is certain to should have reusability, which has the certain difficulty, also have quite a challenge.

(2) The protective function of lithium ion battery management chip design: according to the characteristics of lithium ion battery application designed to implement real-time, effective protection for the battery system.

(3) For lithium ion battery management chip implementation: low power consumption from the perspective of applications, the research of mixed-signal single chip system based on load drive power consumption optimization method.

(4) Layout implementation and results verification: including layout design and post-simulation verification. Among them, the result verification includes two aspects: one is the verification of the accuracy of the function, the second is the accuracy verification of the electrical parameters including the power consumption, and the third is the verification of the achievability of the system.

1.4 The research plan and significance of this paper

According to the research status and design requirements, the research plan to be adopted in this paper is:

(1) considering the mixed signal of the single chip system requirements, respectively, the research method of low power consumption digital and analog circuit, in which the threshold circuit can be used in a standard digital CMOS process, is suitable for use in low speed and low current consumption, so will be deeper to the threshold circuit analysis of the theoretical research and design, including the mismatch to the practical limits to optimizing the power consumption, noise, when the design circuit control and judgment, and the threshold of the specific circuit structure are discussed.

(2) the protective function of lithium ion battery management chip design: including real-time charging and discharging pressure detection and control, which can realize over discharge protection, over charging protection, zero volt charging voltage suppression; Includes real-time two-way charge and discharge current, which can realize the flow of the secondary protection, short circuit protection, and abnormal charging current protection ; In addition, when an external thermistor is used, temperature detection and protection can be achieved.

(3) Load of mixed-signal circuits driven low power design methods: points modeling power consumption, power consumption management strategy and implement three parts to discuss. Applicable to the management of the chip power consumption model is established and the power consumption management strategy after analysis and comparison, the easier to implement a simple control method, and improved, power consumption optimization scheme based on load is put forward.

(4) Low-power hybrid circuit layout design and performance power verification: functional and electrical parameters can be directly verified by circuit-level simulation software (such as HSPICE, VERILOG, POWERMILL, etc.) and compared with the relevant literature indicators; use CADENCE , complete the system layout; verify the system's achievability by extracting parameters from the layout and post-simulation.

It can be seen from the above that the research significance of this paper has at least the following aspects:

(1) The low-power theory and synergistic considerations of each part of the digital-analog hybrid circuit are the theoretical basis for system design and power optimization.

(2) Low power consumption, high precision, miniaturization is the development trend of battery management chips today, and it is an inevitable requirement to meet the application. It is of great practical value to study the low power consumption of battery management chips.

(3) System-level dynamic power management technology for single-chip hybrid circuits not only expands the application of dynamic power management theory in pure digital systems and real-time embedded systems, but also overcomes the existing shortcomings in combination with application characteristics. , develop new content.

(4) The research content and results of this paper have a considerable reference for other battery management chips.

The page contains the contents of the machine translation.