SLUAAR7 March   2024 BQ25731 , BQ25798

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Comparison Of Charging Dock And Onboard Charging Designs
  6. 3Key Design Considerations Of Battery Charging Designs
    1. 3.1 Selection of Charger IC Topology
    2. 3.2 Selection of Charger IC Controller vs. Integrated Designs
  7. 4Battery Charger Features That Simplify Vacuum Robot Charging Design
    1. 4.1 Detection and Protection of Abnormal Charging and Operation
    2. 4.2 Safe Charging With JEITA Temperature Profile for Long Battery Lifetime
    3. 4.3 Low Power Consumption for Service Time and Long Shelf Time
  8. 5Summary
  9. 6References

2 Comparison Of Charging Dock And Onboard Charging Designs

There are two designs for battery charging – charging dock or on-board charging. The charging dock can be separated from the main moving clearing robot with less concern for size, weight, and heat dissipation. The traditional implementation for the charging dock is the isolated AC-DC converter with constant current (CC) and constant voltage (CV) regulation as shown in Figure 2-1. The single-stage approach with microcontroller (MCU) as the central power conversion control is relatively low cost. The major drawbacks are low charging accuracy and the battery voltage sensing point being far away from the battery charging system in the dock. There is increasing concern for the low accuracy of the battery charging from the MCU control and the battery lifetime can be compromised [1]. The several hundreds of kHz switching frequency of an MCU-controlled system is another disadvantage and the size of the design is not a good choice. Thirdly, the contact points for the main charging current flow can have increased impedance with the oxidation effect. As a result, the battery might not get fully charged after the oxidation, and the service time is reduced with a fully charged battery.


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Figure 2-1 Charging Dock Design

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Figure 2-2 On-board Charging Design

The manufacturers look for long-term designs with high reliability to build the brand names. The accuracy of the battery charging, the size of the design, and the battery lifetime are among the major challenges for battery charging. The on-board design as shown in Figure 2-2 can provide charging with inherent high charging accuracy, a smaller design size with higher operation efficiency, and the flexibility for universal USB charging designs, and so on.

The charging accuracy is related to the best utilization of the battery capacity and the battery lifetime. TI battery chargers widely adopted in the vacuum robot’s applications can achieve ±0.5% accuracy crossing the temperature range. For example, the buck-boost charger BQ25730 battery voltage accuracy spec VBAT_REG_ACC is ± 0.5% from 0oC to 85oC junction temperature [2].

The charging design size is reduced from the dedicated charger with a high operation frequency of 750KHz and above and the strong driver circuit is designed to achieve the best efficiency. The operation frequency can be 5 times or higher compared to the MCU. The performance is improved with the dedicated gate driver circuit for MOSFETs to achieve size reduction with better thermal performance. The on-board battery charging designs also provide the advantage of the flexibility to maximize the input source utilization and the potential total BOM cost reduction. The on-board switching charger can adopt an AC/DC adapter or the standardized USB adapter as the input source.