Next Generation Lithium Battery Monitor: How to improve the safety of lithium batteries while increasing accuracy and prolonging runtime

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

In recent years, consumer goods such as vacuum cleaners, electric tools (such as drill bits, saws and screwdrivers) and gardening tools (such as lawn mowers, trimming machines and turf tractors) have been converted from rope and charging battery powered by ropes and rechargeable batteries. Even the previous bicycles that have not been picked up, now also transforming electric bikes and electric motorcycles driven by the battery. These battery packs are typically composed of a single lithium-ion battery, a lithium polymer battery or a lithium-phosphate ion battery.

If the use is improper, it may cause danger, resulting in a fire or explosion. To ensure safe use of the battery, the electronic device in the battery pack monitors the battery to operate the battery only under the conditions specified by the battery manufacturer. These conditions typically include: • Maximum allowable charging voltage.

· Maximum charge and discharge current. · Provided charge and discharge temperature range. Therefore, the key parameters in the battery pack are critical, especially in the battery pack, current, and temperature, because these parameters exceed the limit, the appropriate protection will be triggered.

The measurement data must be accurate so that the designer decides how many margins are included in the design. For example, if the battery specification is limited to 4.3V, the accuracy of the measurement data is ± 50mV, the designer must configure the system to disable charging when the measurement display voltage is above 4.

25V. However, since the actual battery voltage may be as low as 4.2V, in this case, charging will stop before the battery is fully charged, resulting in waste of application capacity and shortened battery life.

The high-precision battery monitor and protector of BQ76942 and BQ76952 and other battery packs are designed for the use of lithium ions, lithium polymers or lithium phosphate ion batteries. These devices support the tandem cells from 3s to 10s (BQ76942) and 16S (BQ76952), which can measure the battery voltage, current, and temperature, and can share data with other circuits, such as the individual microcontroller or electric bicycle in the battery pack. System controller.

BQ76942 and BQ76952 can also use data to automatically touch battery protection, disabling battery packs to prevent overster manufacturers from running, and re-enable battery packs when conditions allow, whether or not to interact with hosts or system microcontrollers. Figure 1 shows a block diagram of BQ76952, which integrates: • Measurement and detection subsystem for monitoring voltage, current, and temperature to detect when parameters exceed the allowable threshold. · Drive external protection FET and chemical fuse.

· A digital host interface subsystem, in addition to the pin control for selecting the function, also supports multiple serial communication standards. · Multiple voltage regulators, one for internal circuitry, two for external use. Figure 1: Box Figure 1 Figure 2 Figure 2 shows the simplified schematic of the 16S battery pack based on BQ76952, using I2C and main microcontroller communication.

The integrated regulator is a microcontroller and an optional external transceiver supply power rail. · Differential voltage of single battery and selection of additional system voltages. · Battery set current and pass charge (coulomb count).

· Interior die and 9 external thermistor temperature reading. Figure 2: The measurement subsystem in BQ76952 and the measuring subsystem in BQ76942 and BQ76952 digitizes various voltages, current and temperature in the battery pack. Since each measurement has a specific requirement, these measurements are obtained in different ways.

For example, the temperature changes slow, so measurement and calculation can be slowly performed. However, battery pack currents may have short pulse activities, if they do not continue to sampling, they may miss. Treatment Voltage and Court Counter ADC generated to supply measurement data, which is used within the device and can be accessed by a separate processor, power tool, or system controller in the battery pack.

These data include: • Differential voltage and selection of additional system voltages. · Battery set current and pass charge (coulomb count). · Interior die and 9 external thermistor temperature reading.

Pins that support external thermistor measurements can also be used for universal ADC input, support no more than ~ 1.8V input voltage. The voltage ADC operates on the measurement loop and inputs a periodic multiplexing between multiple inputs.

The measurement subsystem of BQ76942 and BQ76952 includes multiple programmable options, which can be optimized and trade-offs between measurement speed and precision. As battery-powered consumer goods are increasing, ensuring that they operate in safe voltage, current and temperature range. Battery monitor with integrated functions can help design engineers solve these three key issues while improving accuracy.

For more information on using the TI battery monitor, please check the other resources below.

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