With the progress of technology and environmental protection requirements, lithium batteries are gradually becoming the mainstream of rechargeable batteries, especially in the field of mobile electronics, lithium batteries rely on higher energy density, has almost occupied all markets. However, in some of the relatively high power requirements of the application areas, because the cost of lithium batteries and discharge rate indicators are not dominant, the share is still not high. For example, in the field of electric bicycles, lead-acid batteries still occupy a higher share in the Chinese market, the use of lithium batteries only about 1% market share, while in Europe and the United States accounted for about 50% of developed countries. Such a low market share, the main reason, of course, is the price, but the lithium battery life and safety is also a big short board, these problems can not be solved, will greatly affect the market share of lithium batteries.
And to solve the lithium battery life and security on the need for specialized monitoring and protection circuit, which is a lithium battery compared to other characteristics of a battery, it must be with protection circuit, otherwise it will explode because of heat, previously had cottage Cell phone use without protection circuit lithium battery, the results of battery explosion caused injury accident reports. This can be seen the importance of protection circuit, and before a lot of protection circuit is to use discrete components to take out in terms of cost and reliability are not advantages, for this market conditions, Texas Instruments introduced the industry's first power supply Tools and Electric Bicycles with Single - Chip Battery Management Device bq77910.
Why is the application for power tools and electric bicycles, which from the support of the battery string mentioned. Because the device supports a range of 4 to 10 strings, through the cascade can support up to 20 strings of batteries, the number of lithium batteries to determine its output voltage, 10 strings is the output 34V voltage, in this range, the battery Applications include electric bicycles, electric scooters, portable gardening tools, power tools, and uninterruptible power supplies (UPS), which require certain voltage and current requirements, but are not very demanding. If you want to enter the field of electric vehicles, then the string can be more than 100 strings, this is not the area covered by the device.
The main function of the battery protection circuit is to maintain the safety of the battery under various conditions, to extend the life of the battery to maintain the safety threshold does not exceed the circumstances to ensure that the battery pack fully charged and utilized. The bq77910 is an integrated battery management solution that provides all the necessary battery protection functions and integrated battery balancing features including battery cell overvoltage, battery cell undervoltage, charge short circuit, discharge short circuit overcurrent, battery pack temperature, Open-circuit short-circuit thermistor detection and open-circuit battery cell detection, power-down protection, to prevent power FET overheating and other functions. Its most important feature is to run in an independent device, without an external microprocessor, the internal integrated logic control part, so that the overall program of low-cost possible.
In the device for the high-power battery pack itself in the application will be subjected to great challenges, such as high current, but also requires a large discharge current, charging current is small, the load itself and the battery should be separated. A separate charge and discharge path is also required to reduce the cost by selecting the appropriate protection path element (MOSFET) according to the desired size. In some applications, such as electric vehicles and UPS, also need to quickly charge and discharge conversion. These are the design of the battery pack and the protection circuit has brought great technical challenges.