More and more equipment is powered by batteries, such as portable devices, energy storage systems and electric vehicles, and the battery management systems are a key to extending the battery’s service life. The operating features of the battery management system and ADI's battery management solution are introduced here.
Extend overall battery life by analyzing battery status data in real time
With the rapid development of battery technology, an increasing number of electronic equipment is powered by batteries, such as electric vehicles and hybrid electric vehicles, backup battery systems, grid energy storage and portable device, all of which need accurate and efficient semiconductors to monitor, balance and protect the operation of batteries. The battery life can be extended by 30% by taking advantage of the new lithium battery chemistry through the battery monitoring system (including cell balance and isolated communication network) and by using innovative integrated circuits to improve reliability.
Today, lithium-based chemistry is an advanced technology used in batteries in a variety of markets, including automotive market, industrial market and healthcare market. Different types of lithium batteries have different advantages, enabling them to better meet the power needs of various applications and product designs. For example, LiCoO2 (lithium cobalt oxide) has extremely high specific energy, making it ideal for portable products. The low internal resistance of LiMn2O4 (lithium manganese oxide) ensures fast charging and high current discharge, indicating that it is an ideal choice for peak shaving energy storage applications. The higher capabilities of LiFePO4 (lithium iron phosphate) to withstand full charging and stay at high voltage for a long time make it the best choice for large-scale energy storage systems that need to operate during power outages.
Various battery types are required for different application needs. For example, in automotive applications, high reliability and good charging and discharging speed are needed, while in healthcare applications, peak current sustainability is required to improve efficiency and prolong life. What all of these solutions have in common, however, is that the various lithium chemical compositions exhibit a very flat discharge curve over the nominal voltage range. The standard battery has a voltage drop range of 500 mV to 1 V, while advanced lithium batteries such as lithium iron phosphate (LiFePO4) or lithium cobalt oxide (LiCoO2) batteries show a flat area with a voltage drop range of 50 mV to 200 mV in the discharge curve.
The main drawback of the flat discharge curve is that it faces great difficulties to determine the state of charge (SOC) and the state of health (SOH) ratings of the battery. This requires that the SOC be calculated with very high precision to ensure proper charging and discharging of the battery. Overcharging will bring various safety problems and lead to chemical degradation and short circuit, resulting in fire and gas hazards. Over-discharging can damage the battery, reducing its life by more than 50%. SOH provides information about the performance state of the battery to help prevent replacement of good batteries and to monitor the state of bad batteries before problems arise.
The operating efficiency of the battery can be improved in many ways, such as real-time analysis of SOC and SOH data by using the main microcontroller, modification of charging algorithm, and notification of the user's battery potential (for example, whether the battery is ready for high-current deep discharge in case of power break) as well as guaranteeing the best balance between the battery in bad condition and the battery in good condition in the large-scale energy storage system, so as to increase the overall battery life.
LTC6813-1
In order to improve the efficiency of battery management, ADI launched the LTC®6813-1 battery management solution (BMS). As a multi-cell battery stack monitor, LTC6813-1 can measure the voltage of up to 18 battery cells connected in series, with a total measurement error of less than 2.2mV. The battery measurement range of LTC6813-1 ranges from 0V to 5V, making it a suitable candidate for most battery chemical compositions. All 18 cells can be measured in 290μs, synchronous voltage and current measurement is possible, and low data acquisition rate can be selected to achieve high noise reduction.
The serial connection of multiple LTC6813-1 devices will be able to monitor the battery at the same time in long high-voltage battery strings, and the stackable architecture can support the monitoring of hundreds of batteries. Each LTC6813-1 is equipped with an isoSPI™ interface that supports 1Mb isolated serial communication using a single twisted pair wire up to 100m long and with low EMI susceptibility and emissions. And bidirectional for broken wire protection, so as to realize high-speed, long distance communication with RF immune. Multiple devices are daisy-chained, and all devices are wired by a host processor. Through the daisy chain, bidirectional operation can be realized to ensure the integrity of communication, even in the case of failure along the communication path.
LTC6813-1 is a 16-bit Delta-Sigma (ΔΣ) ADC equipped with a programmable third-order noise filter, which is specially designed for the systems in line with the requirements of ISO 26262-compliant. The balance of the passive battery with programmable pulse width modulation is up to 200mA (maximum), which makes it possible to supply power directly from the battery stack or an isolated power supply.
In LTC6813-1, the charge passive balancing function for each battery and the individual PWM duty cycle control for each cell are provided. In addition, it is equipped with a built-in 5V regulator, 9 general-purpose digital I/O lines or analog inputs, which can be matched with temperature or other sensor inputs, and can be configured as an I2C or SPI master controller to support sleep mode (current consumption is decreased to 6μA). The 64-lead eLQFP package is adopted.
DC2350A-B
ADI has also launched the DC2350A-B evaluation kit to assist customers in product development, which is a multi-cell battery stack monitor demonstration circuit with a built-in 18-cell monitor LTC6813-1. Multiple boards can be connected via a two-wire isolated serial interface (isoSPI) to monitor any number of cells in a stack. The demo circuit is also provided with a reversible isoSPI to support fully redundant communication paths.
RELATED PRODUCTS
Analog Devices DC2350A-B Power Management Development Boards and Kits