Typical Vacuum Cleaner/Robot Sweeper BMS Topology
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In recent years, cordless vacuum cleaners and sweeping robots have become more and more popular, bringing great convenience to people's lives. As the core components of vacuum cleaners and sweeping robots, battery packs are not only related to the product experience, but also to the user's life safety, so they need special attention.
The battery packs for cordless vacuum cleaners on the market are mainly 7-cell battery packs, sometimes 5-cell or 6-cell. The battery packs for sweeping robots are currently the mainstream with 4-cell. According to different needs, the BMS topology of vacuum cleaner/sweeping robot battery packs can be divided into three categories: fuel gauge type, analog front end + MCU type, and hardware protection type. The following introduces these three BMS topologies and the corresponding TI products.
1. Fuel meter type
Figure 1 shows a schematic diagram of the topology of a fuel gauge type BMS. The battery pack consists of only a fuel gauge chip, a current sampling resistor, and a protection switch. The advantage of this solution is that a single chip can be used to achieve power calculation, battery monitoring, and protection.
Figure 1. Fuel meter-based BMS topology
The fuel gauge used in Figure 1 is BQ40Z80. This fuel gauge supports 2-6s battery packs and uses TI's unique impedance tracking algorithm. The power accuracy can reach 1%, and it can track battery aging, and can still ensure high power accuracy when the battery is aged. BQ40Z80 integrates more than 20 protection functions such as overvoltage, undervoltage, overcurrent, short circuit, overtemperature, undertemperature, etc., which can provide all-round protection for the battery. The integrated high-side driver can ensure that the fuel gauge can still communicate with the host even after the protection is triggered. In addition, BQ40Z80 also integrates an internal balancing circuit to ensure power balance between different batteries, extend the overall battery life of the device, and improve the user experience.
In addition, for 4-string battery packs, you can also use BQ40Z50, which supports 2-4s and has similar functions to BQ40Z80. Interested readers can find complete product information on TI's official website, and this article will not go into details.
2. Analog front end + MCU type
Figure 2 shows a schematic diagram of the analog front-end + MCU type BMS topology. This topology is similar to the fuel gauge type, except that the fuel gauge is replaced by the analog front-end and MCU. Compared with the fuel gauge type topology, this solution no longer has its own power calculation function, but it can still calculate power through the MCU combined with voltage and current sampling data. The power accuracy depends on the sampling accuracy and power algorithm.
Figure 2. Analog front end + AFE type BMS topology
The analog front end used in Figure 2 is BQ76942, which supports 3-10s applications. BQ76942 also integrates multiple protection functions such as overvoltage, undervoltage, overcurrent, short circuit, overtemperature, undertemperature, etc., which can provide all-round protection for the battery. The integrated high-side driver can ensure that communication with the host can still be carried out even after the protection is triggered. In addition, BQ76942 also integrates an internal balancing circuit to ensure the balance of power between different batteries and extend the overall battery life of the device. For low-side protection solutions, TI's BQ76930 (6-10s) and BQ76920 (3-5s) are recommended. Of course, they can also be used with TI's high-side driver BQ76200 to achieve high-side protection. For MCU, TI's 430 series has a wealth of products that can meet various application requirements. Since this article mainly focuses on analog products, it will not be repeated here.
3. Hardware protection type
Figure 3 shows a schematic diagram of the hardware protection BMS topology. The battery pack is composed of only a protection IC, a current sampling resistor, and a protection switch. The advantages of this solution are obvious: simple and cheap. But the disadvantages are also obvious: a. Limited functions, only supporting protection functions, and the protection value cannot be configured, and the flexibility is poor; b. It does not have the power calculation function, and the host side needs to have additional power calculation capabilities. Therefore, this topology is more suitable for low-cost or host-side strong occasions.
Figure 3. Hardware-protected BMS topology
The protection IC used in Figure 3 is BQ77915, which supports 3-5s applications. For applications with a string number of 5s or more, several BQ77915s can be cascaded and used to support up to 20s. BQ77915 integrates multiple protections such as overvoltage, undervoltage, overcurrent, short circuit, overtemperature, and undertemperature. The overcurrent protection delay is configurable. In addition, BQ77915 also integrates an internal battery balancing circuit to ensure the balance of power between different batteries, extending the overall battery life of the device.
If the actual application does not require battery balancing, the more cost-effective BQ77905 can be selected.
For the above two protection ICs, TI provides models with different configurations for customers to choose from. If the existing models still cannot meet the needs of actual applications, you can contact the corresponding sales team to customize products that meet the requirements.
In addition, some products have higher requirements for protection and need to have two-stage protection to further improve the protection level of the battery pack. For users with two-stage protection requirements, TI's BQ7718 series products are recommended. Like BQ77915, TI provides a variety of configurations for users to choose from, and if there is no suitable model in the product list, you can also contact the corresponding sales team for customization.
Li, Jayden
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