2015-05-17Protection of lithium ion battery: building voltag
The safety of lithium ion batteries in a narrow tolerance operation and the overall battery life are considered while the operation is carried out. In order to ensure the correct operation of the voltage level, engineers can build voltage monitoring function integrated into various by semiconductor manufacturers specialized IC, including ADI, ATMEL, letter beauty integration, skyworks, meaning law semiconductor and Texas Instruments, and other energy acquisition design.
Lithium ion batteries are usually charged to the nominal voltage of 4.20 volts to about + 50 MV tolerance. The following characteristics of the charge distribution (Fig. 1), the cells reached through the constant current phase, quickly brought the charge level and constant voltage phase to bring the cell to its maximum charge level this set point voltage.
Although the application of the 4.2V to the set point of high voltage can temporarily increase the cell capacity, a higher voltage leads to changes in the cell interior. Under the conditions that the cells are subjected to long periods of overpressure, the lithium ion begins to the plate on the anode, reducing the number of free lithium ions and the generation of cell charge capacity and total cell life loss. In addition, the continued application of the voltage level exceeds the set point induced oxidation leading to the production of carbon dioxide. If the overvoltage conditions allow to continue to exist, increased CO2pressure may cause the safety film inside the cell rupture, risking the catastrophic thermal runaway, even burning.
Figure 1: the characteristics of constant current / constant voltage charging curve leads to cell stress and damage for high voltage lithium ion battery cell to bring the best charge beyond the application.
To prevent overvoltage conditions, engineers can from a series of specialized equipment, including IC design into a limited number of goals and cells typical of lithium ion battery, designed for large multi stack integrated circuit, specifically to room temperature energy acquisition design design integrated circuit chooses to use a highly integrated MCU, even based on software solutions.
The protection of lithium ion battery
The designer can protect the lithium ion battery including the use of all available lithium ion rechargeable IC cases, including STMicroelectronics STBC21, Scarlett AAT3783 or TI BQ24314A, only a few cells.
These devices usually provide signals when the overvoltage occurs is triggered. For example, ST STBC21 built-in overvoltage protection function to trigger the alarm when VBAT storage device pin on the voltage - more than 4.23 factory settings V + 20 mV.
With Skyworks AAT3783, the engineer can use the factory settings of the over voltage trip point or external resistor connected to the OVP pin of the special set point. When the input voltage is higher than the jump point, AAT3783 P off the internal n-channel field effect transistor, disconnect the input.
Similarly, the internal TI BQ24314A monitoring the input voltage and the use of switch in voltage conditions. Disconnect rapid case: the BQ24314A, the internal FET switch off in less than a microsecond. After the return to the input voltage to the appropriate level, but FET switched on again after a delay, to allow the input voltage to stabilize.