Power banks are becoming more and more popular as battery capacity outstrips the runtime of personal electronic devices like smartphones and tablets. High-performance CPUs, large sizes and high-resolution display panels also make runtimes shorter. This creates an demand for a fast-charging backup battery such as a power banks.
Traditionally, a 5V USB is the standard power supply for mobile devices like smartphones and tablets. Due to the current capacity limitation of mini USBs, a 5V power supply can only deliver about 10W of power at best, which could take more than 6 hours to charge. With the battery capacity of mobile devices increasing, long battery charging times become a headache for consumers.
To improve the user experience, high-voltage (>5V) charging method provides more input power and shortens charging times, while maintaining the same cable current of 2A. Beyond high-voltage charging, many power-bank vendors are also creating more intelligent power banks through the integration of a battery fuel gauge, which allows users to see power-bank status and estimated charge and discharge times A trend is to get the power bank to be smarter. It enables users to be informed of the status of power bank, estimate the charging and dis-charging time. Authentication is also becoming a trend, where the end application and power bank require authentication before charging. The idea is to preserve the overall battery life of the application.
Power-bank designers in Asia are some of the early adopters of these up-and-coming features; one leading power-bank vendor in China uses TI’s 2.4 GHz CC2543 system-on-chip (SoC) and bq25895 in its new designs. In the vendor’s case, the input needs to support 12V/9V/5V adapters with a 4A maximum battery-charging current, while the output discharging power is 5V/2.1A.
Figure 1 is a typical block diagram of a smart power bank. The 8051 core, 32kB flash, 1kB RAM CC2543 SoC acts as the system controller as well as the wireless transceiver. The key factor in this design is using the CC2543 device’s proprietary radio to achieve low power and low-cost Bluetooth® Low Energy beacon functionality.
The bq25895, a single-cell fast-charger provides a handshake with the adapter autonomously and supports high-voltage charging (buck). Its charging current can be as high as 5A. When in USB On-The-Go mode, the bq25895 can work as a boost and output a stable 5V (with a maximum output current of 3A) for powering a connected end device like a smartphone.
The TPS2514 USB-dedicated charging port controller provides a handshake with the connected device to make sure that the device can extract the maximum power from the power bank.
Figure 1: Block diagram from a smart power bank supporting high voltage charging
Several companies have provided different protocols for high voltage charging, including TI. More and more smartphones and power banks now include a high-voltage charging feature. In this fiercely competitive market, the bq25895 and CC2543 SoC can bring extra value to enable full fast-charging capabilities and increase the quality of your products. Learn more about the benefits by visiting the product folders and let us know what you’re looking to design fast charging with in the comments.
Additional resources
- Read more about designing power banks with MaxCharge™ technology in the blog post: “Eliminate battery anxiety with portable power in your pocket.”
- Check out the user’s guide for designing system-on-chip solutions for 2.4GHz applications.
