To understand the advantages of Active-Semi’s new ACT2800 family of Power Bank ICs, we have to look at a typical application. The Power Bank is essentially a battery in a sealed case used to supply power to a device whose battery has been exhausted. Usually, you connect a USB cable from a power source, such as a laptop, to supply power to charge the Power Bank’s internal battery. Then, you take the charged up Power Bank and its cable, and use it to connect to a smartphone or similar device with a depleted battery. Thus, the Power Bank serves to recharge the battery in the device with a depleted battery. This requires the Power Bank to provide a means to control the charge on its internal battery and also control the output to the device whose battery is depleted. Fig. 1 shows a simplified Power Bank circuit.
In a typical Power Bank implementation the associated battery-powered device is a smartphone with a micro-USB connector for charging its battery. The power input to the Power Bank is provided through a micro-USB connector and the Power Bank output will also use a USB connector. To charge the Power Bank’s internal battery, you use a cable with USB at one end and a micro-USB on the other end. You plug this cable into a USB port on a computer and then plug the micro-USB connector into the Power Bank. When the Power Bank’s battery is fully charged, you use the same cable by plugging the USB connector into the output of the Power Bank and the micro-USB connector into the charging input of the smartphone.
It is also possible to simultaneously connect both USB cables (i.e. provide input power to Powerbank, as well as simultaneously connect and charge phone battery as well. ACT2801/2 provides a direct power path from input to output with programmable current limit while providing power to switching charger. The output has higher priority than battery charger if the programmed input current limit is reached.
Most of today’s Power Banks require multiple ICs and additional external components to provide the charging and battery management functions. The ACT2800 family’s ACT2801 and ACT2802 ICs reduce the system footprint and minimize design complexity, while leaving room for larger batteries and reducing total system cost.
The ACT2801 and ACT2802 are functionally similar with different power handling capability, as shown in Table 1. They are both space-saving and high-performance low-profile single-chip solutions for a switching charger, boost converter and LED indicators. Table 1 shows the differences between these ICs. A high frequency switching frequency allows small size external inductors and capacitors.The ACT2801 and ACT2802 are both complete battery charge and discharge power management solutions for applications using single-cell lithium-based backup battery packs. Both the ACT2801 and ACT2802 provide similar functions. They charge the battery with a full cycle of preconditioning, fast charge with constant current and constant voltage until end of charge. These battery chargers are thermally regulated at 110 °C with charge current foldback.
The boost converters in the ACT2801 and ACT2802 both step the internal battery voltage up to a maximum of 5 V, with a programmable adjustment to a lower voltage. They feature high efficiency, constant current regulation, short circuit protection and overvoltage protection.
Four external LEDs driven by a 3.5 mA constant current source are used to indicate battery level and charge status for the ACT2801 and ACT2802.
As shown in Fig. 2, the ACT2801 has a bi-directional architecture featuring a synchronous buck/boost converter you can configure as either a buck to charge the battery, or a boost to charge the external battery-powered device. This architecture allows higher charge current and higher conversion efficiency than traditional charge/discharge circuits.
The ACT2802 has a similar architecture with the primary difference of lower on-resistance for its internal power MOSFETs, as shown in Table 1.