Ultra-low power lithium battery management system circuit design

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Overview:
In order to meet the application of a micro-power meter and improve safety performance, a design scheme of ultra-low-power lithium battery management system is proposed. The scheme uses a bidirectional high-end micro-current detection circuit, combined with an open circuit voltage and a charge integration algorithm to achieve power detection. Use a button battery instead of a DC/DC step-down circuit to minimize power consumption. The system implements basic protection, remaining power detection, and fault logging. The lithium battery management system was verified on the meter and the results showed good stability and reliability with an average operating current of only 145 μA.

With the rapid development of electronic technology, the application field of instrumentation has been continuously expanded, and battery power has become an important choice. The battery management system is an effective guarantee for battery safety. Most of the current battery management systems are designed for large-capacity battery packs and short-life time applications. The power consumption of such management systems is large, the cycle time of the battery is short, and the power consumption of the management system itself is not low. Used on low power instrumentation fields. A gas remote monitoring instrument, the average system current is only a few milliamperes, and requires continuous operation for more than 6 months at low temperature. In order to meet the application of this project, this paper introduces a design scheme of low temperature intelligent lithium battery management system, for 20Ah. Four strings of 8 and 32 single cells are managed. Basic protection, power metering, charge balancing and fault logging. The experiment verified that the functions of the system were good and met the design requirements.

1 The overall structure of the system The low-temperature lithium battery management system is mainly composed of basic protection circuit, fuel gauge, equalization circuit, secondary protection, etc., as shown in Figure 1.

Figure 1 Low-temperature lithium battery management system structure based on low-power considerations, the design uses many low-power devices, such as the processor using MSP430FG439 low-power microcontroller; the voltage reference uses REF3325, the reference power consumption is extremely low only 3.9 μA; the op amp uses the LT1495 with an operating current of only 1.5μA; the digital potentiometer uses the AD5165 with a quiescent current as low as 50nA. Power management circuits are added to intermittent operating circuits with large operating currents to reduce energy consumption.

The rated voltage of the low-temperature battery pack is 14.8V, which is formed by connecting four groups of batteries. Each group of batteries contains 8 single cells, and the normal working voltage is 2.5~4.2V. The voltage of each group of cells is collected in each collection cycle, and the processor issues an instruction to the protection execution circuit according to the voltage level to perform a corresponding protection action. The equalization circuit is realized by a single chip microcomputer and a triode, instead of the equalization dedicated chip. The system records the maximum value of voltage current and temperature, the battery used time, remaining power and other abnormal information in the storage device. The processor provides a TTL communication interface, and the on-site computer can read the logs in the storage device through a TTLRS232 conversion module. Protection failure occurs during the charging process in order to prevent an abnormality such as an MCU crash. A secondary protection circuit is added. If the voltage exceeds the preset value, the secondary protection circuit will be activated to blow the three-terminal fuse to prevent the accident.
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