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Battery cell battery monitoring IC Detailed

In Electronic Infomation Category: B | on April 13,2011

Battery cells, super capacitors and ADM489ARZ datasheet and fuel cells need to carefully monitor the core to expand, such as electric cars and ADM489ARZ price and hybrid cars in the use of energy storage system to extend its life and ADM489ARZ suppliers and ensure their safety (Figure 1). The battery is to develop a range of automotive applications. Micro-hybrid cars using the traditional lead-acid batteries 12V, and AC generator - motor unit, car parking can make the engine shut down. When the throttle, the engine will be smooth to start, and then normal operation. The hybrid cars have more batteries, such as the Toyota Prius, Honda Insight and Chevrolet Volt. The battery produces a voltage exceeding 200V. Traditional chemical battery cell type is NiMH (nickel metal - hydride), but many in a lithium chemical technology provided under the weight of higher energy (Figure 2). All electric vehicles (such as Teslas Roadster and Nissan Leaf) has the largest battery, which battery pack voltage range from 300V-400V.

Figure 2, electric cars and UPS applications may use a variety of cell types, they need to measure the IC for battery monitoring (Linear Technology Corp).

Battery voltage higher power under a given current will be lower, thus reducing the expensive copper cable diameter. More importantly, the higher the output voltage can be used more motor windings. 2004 Toyota Prius adds a boost converter, the battery voltage increases from 200V to 500V. This step makes the Toyota redesigned the propulsion motor, the torque increased from 350 Nm to 400 Nm, and power increased from 33 kW to 50 kW.

300V battery string of data centers will be used for UPS (uninterruptible power supply) backup power supply. In this application, lithium-ion batteries are replacing lead-acid batteries. Better use of the lithium-ion vehicle weight energy density, that is, the energy per pound or per kilogram. UPS application of the use of the volume of lithium-ion battery energy density. Data center space is very expensive, although prices of lithium-ion battery system may be higher, but the space it occupies only a quarter of lead-acid battery system. This fact makes the data center is usually the battery and the converter system placed in a room. Centre is considering removing some data converters, and the DC power transmission can accept DC input to the data center servers.

The small size of lithium ion batteries, they are available in power levels and data center applications, the same benefits. Some network-level solutions tend to use fuel cells, and high-pressure fuel cell and electrochemical cells requires the same meticulous care. There are special requirements of fuel cell batteries, fuel cell batteries during use, there are two polarities, will show a variety of failure modes. IC manufacturers are to make their own battery monitor chip under the battery cells to adapt to the negative voltage.

When the super capacitor group care, there will be a similar problem. Users want all the energy capacitor, and this means to its discharge to 0V. If this occurs, the capacitor dielectric effect will the emergence of a negative voltage, typically up to-0.5V. Some IC manufacturers are improving their own battery pack chips, so that it can withstand negative potential. Super capacitor energy storage than batteries or fuel cells, so small for high energy applications (see enclosure 1, "the chemical properties of the battery").

Battery cell monitoring

Car with UPS manufacturers want to accurately monitor a battery in each battery cell. Analog Devices, hybrid and electric automotive industry marketing manager Paul Maher said: "You definitely do not want to because of a bad battery cell and let the car to stop, but the circumstances have to stop the overheating." Automotive battery monitoring is critical. He added: "A laptop computer battery is expected to be used for two years, but a car battery should be sustainable for 10 years."

Measurement must be very precise, because the number of millivolts may represent a large number of charge. There is a common mode measurement problem, it should be in the hundreds of volts common mode potential case, try the accurate measurement of the battery cell. This measurement is not to use the integrated ADC for DC measurements. The battery voltage may kHz rate to make a change, because the chopper motor drive circuit action. In addition, the measurement system also need to have blocking measures, because the battery voltage is very dangerous. Chip must be low power consumption, so as not to consume battery power. In addition to the difficulties of measuring itself, it also must be sent to a car or measurement data center point of multiple targets.

Battery monitoring circuit of the first challenge is accuracy. Modern lithium-ion battery has a flat discharge curve. Power marketing manager, Texas Instruments Matthew Borne said: "In the state of charge of the battery cell when the estimation, 5 mV of the measurement error represents 10% of errors." Battery discharge must be stopped, otherwise it will damage the battery, so a higher accuracy maps directly to a larger scale; a 4V battery cell on the accuracy of 8 mV corresponds to 0.2% accuracy. System to provide 0.2% accuracy, voltage reference in the time and temperature on the accuracy of all must be about 0.1%.

Once a sufficient accuracy to face another problem: measuring a dozen others may 4V battery cell battery cells in series. If you intend to use the attenuator to measure the battery cell voltage, precision resistor divider may be required (see attachment 2 "common-mode problem"). Film resistors and not precise enough, not with the temperature kept close enough track of.

Capacitor can be charged to the battery cell voltage, and then they switch to a rack-based potential. This so-called flying capacitor (flying-capacitor) method can work, but there are drawbacks. For example, Maxim Integrated Products companys automotive and industrial battery products business

Manager Stephen G LaJeunesse that the capacitor will start in the battery cells of different potential mismatch between the charge transfer. He said: "They also need high voltage switch, which switches have their own loss," thereby reducing the efficiency of the circuit.

Linear Technology Corporation Jim Williams, senior scientist developed a new circuit, using a small inexpensive transformer check each battery cell voltage (Figure 3 and Reference 3). Circuit works well, but the transformer to increase the cost, but also a failure due to vibration.

Figure 3, the common mode voltage of the circuit to solve measurement problems, is through a small isolation transformer, transmission battery cell voltage and diode drop.

Battery monitoring IC manufacturers to avoid common-mode problem is the chip floating voltage in the battery pack. They convert the analog measurements to digital values, and then sent to the other under these digital bit chip daisy chain. This step can be to get rid of the resistive attenuator, and the measurement will not have any common-mode attenuation error (Figure 4).

Placed in the measurement chip daisy chain, there are other important requirements. It requires an isolated insulator, rather than multiple. Decades ago, engineers sent through insulation barrier to analog voltage. Battery monitoring chip architecture is the current trend. Analog voltage measurements, and then the voltage is converted to digital bits. The digital data transmission over a blocking barrier there are many ways (Reference 4). Coupler can be used, blocking capacitors, transformer isolation, RF isolation, and even magnetostrictive isolators. If it is sent through the analog isolation barrier level, you can use delta-sigma modulator, such as Avago products.

Ensure accurate measurement once, and to address the common-mode problems, the design must also be sure to meet the power requirements. Most of the battery pack itself can provide the power battery monitor IC, which means not charging the battery will run out of power. Another equally important is that each chip must have the same power, so the power consumption of a chip not only over the surrounding chip, resulting in a battery cell imbalance. Alternatively, you can use car batteries or external power supply isolated power supply, such as the Analog Devices chips for its control did (Figure 5). This monitoring circuit does not consume battery energy.

When designing measurement systems, it must be sent in a data communication link. Some manufacturers will be a simple local serial protocol (such as serial peripheral interface SPI) is converted to a high-level protocols such as CAN (Controller Area Network) bus. CAN communication in automotive applications for decades in time, proved its reliability.

These considerations on the measurement system is only basic needs. Car manufacturers to meet the reliability and liability concerns, we must measure the battery pack to each core. In order to minimize the number of required measurement converters, most IC manufacturers in their own battery monitor chips using high-pressure, a fault-protected multiplexer, the chip to accurately measure 4? 12 battery cells, then measured results through a serial bus, sent to the daisy chain to the next one chip.

When assembly workers or machine using hot-plug replacement method, the measuring circuit connected to the battery, they produced another important reliability issues. This method does not guarantee that the workers which is only connected to the first battery cell. Battery cell detection for any arbitrary line connecting the core to the silicon into a lot of current. Maxims JaJeunesse that the chips must be reinforced nodes, he pointed out that the chip does not need dielectric process. He said: "DMOS and CMOS have done the job, but you must know the bias circuit element method, and how short the transistors within the well and the gate." He warned IC designers, use the guide ring to solve the hot carrier son into the problem.

Most manufacturers supply both external and on-chip temperature detection, and thus system designers can measure the ambient temperature and battery cell temperature. Then, designers can charge them with security algorithm to increase the temperature factor. Reliability makes the car manufacturers made redundant measuring system-wide requirements (Figure 6). In these structures, a set of links to the chip to do daisy measurement, the other chip is used to set the maximum and minimum limits of the comparator, monitoring the situation measured these effects given the demo map). Intersil and other manufacturers to ensure that the serial communication between the chips are passive, and the reason is: If a chip case there is an electrical failure, it still allows daisy chain communication by all other chips. Most of the battery pack there is bi-directional serial communication measurement chip, can use their own system BMU (Battery Management Unit) chip micro-controller check to ensure that the chip power and work.

monitoring measurement situations In addition to this system-level redundancy

outside, many manufacturers still build their own chip redundancy and self-test function.

Intersil Corporation Kenneth Lenk automotive product marketing manager, said such chips include a variety of voltage reference. He added that the company also added its own chip hidden in the DAC, for correction and self-test.

Many manufacturers have emphasized that their device has a passive communication link. Failure of these links even when the chip will continue to work. Analog Devices, precision amplifier portfolio manager Sam Weinstein said manufacturers not only to establish internal redundancy, but also to ensure that the redundant security chip operation. He pointed out that, BIST (built-in self test) is very expensive, but it is the foundation to meet the requirements of the automotive industry.

A project of the committee is the vehicle battery systems and redundancy to achieve fail-safe ISO (International Organization for Standardization) 26262 standards, ISO organization is expected to publish the standard this year. Developers adopted this standard, you can provide them with electric vehicles in the analog, digital and software components of a complete guide. Texas Instruments, Analog Devices, STMicroelectronics and NXP and other companies for these mission-critical in the provision of advanced analog and digital transmission module hardware.

Battery Environment

Addition to vehicle battery measurement, it also enables the system to be experienced in the modern car survive the harsh environment. All of these components are subjected to vibration and acceleration. For example, through the chain hanging on the railway transport vehicle maximum acceleration occurs when the surface mount chips and passive components to be shock.

System must also be able to withstand the temperature over a wider range of consumer electronics. For example, the battery can not afford to +125 C core temperature. And, most of the chip can work to +85 C temperature, Maxim and Analog Devices chips can work to +105 C. Intersil and other manufacturers to car manufacturers specify the temperature in the work of the chip. Low temperature will also cause problems. Transistor base-emitter junction voltage and transconductance decrease with temperature rise, resulting in oscillation of the amplifier.

Battery measurement system must be designed to withstand EOS (electrical over-load). For example, when a mechanic in the engine disconnect a battery cable running to determine whether the alternator work, this phenomenon occurs. At this point, the alternator will be sent to the electrical system of a 100V pulse. Although the electric vehicle battery pack may not be subjected to this pressure the chip, but the bus connecting the battery cell may be outdated in a large current flows damaged, because the battery voltage to generate a large overshoot.

EMI can interfere with measurement, is the electric vehicles in one of the greatest environmental challenge (Figure 7). All traces and high-impedance nodes are affected by EMI, EMI may damage the battery cell voltage measurement. Linear Technology Corporation, according to Tim Regan, applications manager, said AC ripple may be everywhere. The ripple from the converter chopping frequency, and added to electrical noise on the motor.

Regan added: "The basic method of decoupling is very effective." However, the decoupling is only a beginning. Must also pay attention to the noise source, PCB (printed circuit board) layout, and shielding.

Figure 7, the experimental structure can be injected to the current measurement system to ensure that the chip can withstand high current.

foil covered box isolated external radiation, it will not affect the measurement (Linear Technology Corp).

Once removed from the measurement of EMI, EMI may result also need to consider the daisy chain serial communication between the chip losses. Communication link between the chips may have different lengths. Intersil Corporation Lenke, said: "The whole chain may have 400V? 600V electrical potential."

Electric vehicle designers must also address the problem of the magnetic field, the magnetic field from the car charger, battery and the motor back and forth between the high current. Shield the magnetic field is very difficult and requires a heavy metal plate or plates to the magnetic field and electronic components to isolate. With all other noise, like a good way to solve this problem is the source of inhibition. All the major currents are confined to a small loop in the region.

In the automotive battery monitoring system, the cost is the most important issue. For the mass market cars are installed with the battery pack can not be 60 dollars a dozen chips. In this sense, the design of automotive design is much more difficult than the military, because the car companies can put unlimited funds, to solve the vibration, temperature, and high-performance needs of the market. Linear adjustment of product the company Signal Erik Soule, general manager of the view that there must be high performance and low-cost chip that can supply large quantities, have a good yield.

Simulated battery monitoring chip company has been considerable progress. Device must have high accuracy, small size and good properties, because the applications are EMI and electrical stress. Car manufacturers require redundancy and fault protection. Although the supplier can provide * The evaluation board, however, if the system directly to the board for a place, it can work remaining questions. You must understand the application of the measurement, noise and interference problems before with good design and layout techniques. Through careful design and careful screening, monitoring system to produce a vehicle propulsion system can continue to work more than 10 years.

Enclosure 1: The battery chemistry

Battery cell manufacturers often publish a report praised their battery is perfect, but you need to read the users * of battery cells, battery cells to get information about the real limitations of the concept of chemistry (Reference A). Lithium ion battery cells have a flat discharge curve, it is necessary to measure the millivolt accuracy (Figure A).

Lithium-ion battery over charge or full charge will cause damage to the storage under. Unlike most other similar chemical properties of the battery cell, lithium-ion battery will discharge to 0% can also cause damage (Figure B). Therefore, the Chevrolet Volts battery management system will be the car 16 kWhr battery charge to 90% and 25% capacity, to stop the discharge. This method can be used to obtain the battery capacity of 10.4 kWhr, but the extended cycle life.

Battery energy density and the designer must make trade-off between power density (Figure C). An energy density of batteries has accepted a large amount of energy stored, but must be slowly released. And an acceptable power density of batteries have low internal resistance, so do not cause a large power pulse damage caused by battery cells.

Although the discharge of a battery cell to 0% may cause damage, but it will not endanger the user. On the other hand, the battery may overcharge the core of a threat. Any battery cell in the high current will cause the battery cell temperature, boiling, or even an explosion. Lithium ion battery cells a particular problem at this point. Some flammable lithium ion battery electrodes, because the battery is lithium metal core. Legend of the company Tesla and Chevrolet have the battery pack during the test fire damage to the car. Older lithium-ion batteries with cobalt, the most likely fire. Short and piercing can provide sufficient energy to produce a conductive plasma, resulting in more short-circuit near the battery cell.

Newer iron phosphate lithium-ion batteries is not easy to catch fire; they sizzle will be issued and slow fever. For this reason, most major car companies are using lithium iron phosphate batteries. Disadvantage of lithium iron phosphate is the energy density of its weight is smaller 33%? 50%, so that the heavier the battery. Therefore, the major automotive companies any different propulsion systems (such as used in electric vehicles) are very cautious.

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