Technology Sharing-How to improve the temperature measurement accuracy in the battery management system.

When the lithium battery is operated at a temperature range beyond the battery manufacturer's rules, there is a risk of thermal runaway, which may eventually lead to fire or explosion. Therefore, in order to ensure the safety of the system and meet the requirements of various standards, it is necessary to disable the battery whenever the battery temperature exceeds the specified temperature range. However, knowing when to disable the battery depends on the accuracy of the battery monitor and maintainer temperature measurement system, which is essential to ensure the safe operation of the system. As mentioned in the article 'Next Generation Battery Monitor: How to Improve Battery Safety While Improving Accuracy and Extending Operating TimeThe system of mass consumer goods such as electric tools and electric bicycles operates safely. In this article, we will further study the temperature monitoring of lithium batteries, including the correct equipment for the safe operation of the system. The latest products in the Texas Instruments battery monitor and maintainer series, BQ76942 (3 batteries in series [3S], up to 10S) and BQ76952 (up to 3S to 16S), integrate a 16-bit/24-bit delta-sigma analog-to-digital converter (ADC) ), multiplexing between various voltage measurements, including measuring internal chip temperature and external thermistor. Both battery monitors support the use of external thermistors on up to 9 device pins for temperature measurement, which allows system planners to more sensitively choose where to measure temperature in the battery pack. A separate thermistor measurement value and internal chip temperature reading can be specified to be used as battery temperature, field effect transistor (FET) temperature, or neither. BQ76942 (10S) and BQ76952 (16S) include an internal chip temperature measurement based on the ADC using its internal reference to measure the ΔVBE voltage. The voltage is converted into a temperature reading, which can be read through the serial communication interface. The maintenance sub-system uses the measured value specified as the battery temperature to identify the battery temperature being too high/low during charging or the temperature is too high/low during discharging, and to confirm whether the battery is allowed to balance. The thermistor that specifies the temperature of the FET is used to identify the FET overheating. Any thermistor that is enabled but not designated for battery or FET temperature will be used for temperature reporting, but will not be used by the maintenance subsystem. The thermistor is measured when it is connected to the internal pull-up resistor connected to the REG18 (~1.8V) low dropout voltage regulator, as shown in Figure 1. Figure 1: Using an external thermistor to measure the temperature of the internal chip also determines whether battery balancing is allowed, and whether the equipment should be placed in a closed state to prevent incorrect operation when it exceeds its specified operating temperature range. During operation, the device uses an internal pull-up resistor programmable to 18kΩ or 180kΩ to automatically bias one thermistor at a time. The pull-up resistor is measured during factory debugging, and its value is stored in the device in a digital method for temperature calculation. The voltage ADC uses the REG18 voltage as a reference to measure the thermistor pin voltage proportionally. The voltage on each thermistor is measured every one to three measurement cycles. The original ADC count value can be obtained through the DASTATUS6() subcommand. In normal mode, the device converts these measured values u200bu200binto temperature every 250ms; in sleep mode, the device converts these measured values u200bu200binto temperature every other measurement. BQ76942 and BQ76952 use the fifth-order polynomial measured by ADC to calculate the temperature. These devices include default polynomial coefficients for the following: The temperature calculated by each active thermistor is in units of 0.1°K, which can be read using the serial communication interface. Semitec 204AP-2 thermistor with 180kΩ pull-up resistor (200kΩ at 25°C, B25/85 u003d 4,470 k). Semitec 103-AT thermistor with 18kΩ pull-up resistor (10kΩ at 25°C, B25/85 u003d 3,435 k). Custom coefficients optimized for use with other thermistors can also be written into registers or one-time programmable memories. Conclusion The BQ76942 and BQ76952 battery monitors and maintainers include a high-performance quantum system. This subsystem integrates an internal chip temperature measurement and supports up to 9 external thermistors for battery or FET temperature measurement. These devices can be used in various applications such as power tools and electric bicycles to ensure system safety by monitoring the battery temperature and disabling the battery pack when the situation becomes risky. Disclaimer: The articles published on this site are all from the Internet and do not represent the views of this site. If there is any infringement, please contact to delete WeChat: Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact delete A: In Europe, electric bicycles have become a hot sale