Multi-cell lithium battery charging management solution-TPS54201 application in sweeping robot
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With the popularity of smart homes, sweeping robots have become the new favorite of young urban white-collar workers and have been promoted to one of the three essential household appliances. Sweeping robots can not only complete trivial sweeping tasks, but also recharge automatically. They are usually powered by 4 lithium batteries in series. At present, the charging management of sweeping robots on the market is mostly implemented with discrete solutions. As shown in Figure 1, the MCU samples the charging voltage and charging current of the battery in real time, and the output PWM is controlled by the MOS through level conversion to achieve closed-loop control. Due to limited MCU resources, the switching frequency is usually below 50K Hz, there are many peripheral devices and the power inductor is large. In addition, the discrete solution does not have overcurrent and short-circuit protection functions.
Figure 1 Discrete solution VS TPS54201-Li-ion battery charging management
TPS54201 is a 1.5A constant current driver with an input voltage range of 4.5V to 28V. It regulates the current by controlling the PWM pin. 150mΩ and 70mΩ MOSFETs are integrated in the SOT23-6 package, which can achieve a conversion efficiency of up to 95%. As shown in Figure 2, the battery voltage is sampled by the MCU, and the PWM is output to control the charging current of the TPS54201. Only a 4.7uH inductor and very few peripheral components are required to form a complete lithium battery charging management solution. The charging current can reach 1.5A, supporting 1 to 6 lithium-ion batteries, and also supports lithium iron phosphate batteries. Compared with discrete solutions, the TPS54201 charging solution no longer requires level conversion circuits, current sampling circuits, MOS tubes and rectifier diodes, and integrates over-current short-circuit protection functions.
Figure 2 Multi-cell lithium battery charging solution based on TPS54201
In order to better protect lithium batteries, the charging process is generally required to be divided into four stages: trickle charging (low-voltage pre-charging), constant current charging, constant voltage charging, and charging end. Figure 3 is a charging management flow chart of TPS54201. Taking four lithium batteries as an example, when the adapter is inserted, the initial PWM duty cycle D_PWM=0. When the MCU detects that the battery voltage is less than 12.8V, D_PWM=10% is set to enter the pre-charging stage. At this time, the charging current is 10% of the rated current. When the battery voltage rises and reaches 12.8V, D_PWM=100% is set to enter the constant current charging stage, and the charging current rises to the rated current. As the charging voltage rises and reaches the rated voltage of 16.8V, it enters the constant voltage charging stage, and D_PWM is gradually reduced in steps of 1% to keep the battery voltage close to the rated voltage of 16.8V. Finally, when D_PWM is reduced to 10%, the charging current is equal to the cut-off current (usually 10% of the rated charging current), and D_PWM=0% is set to charge end.
Figure 3 TPS54201 charging management flow chart
In general, the TPS54201 charging solution has few peripheral devices, simple control logic, integrated overcurrent and short-circuit protection, and supports up to 6 batteries and 1.5A charging current. It is very suitable for use in sweepers and other cost-sensitive applications.
Author: Stone Zeng (South China Mass Market)
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