Today, system designers need to be much savvier about power management. Because of the ever-increasing number of functions and applications, there are greater demands on battery capacity. Users also demand shorter charge time, which requires faster charge currents.
A single charger may not be able to support the high charge current needed, however, because of the thermal limitations in semiconductor packages. Nobody likes handling a hot device. By adding a secondary charger in parallel with the main charger, you can boost the total charge current by 75%-100%. This is called a dual-charger system. It is generally a better solution for supporting charge currents greater than 5A and distributing heat across the board.
Generally speaking, a dual-charger system includes a main charger and a parallel charger. As you can see in Figure 1, the main charger takes control for the entire charging process, while the parallel charger is disabled by default and usually only operates when a high charging current is necessary.
Figure 1: Dual-charger system simplified block diagram
It is not necessary to use two full-featured charger ICs for a dual-charger application. A dedicated, specially designed parallel-charger IC still does the job well and saves component costs, since a parallel charger does not need all the functions of the main charger. As a dedicated parallel charger, its charge should be disabled by default and activate only when necessary. Table 1 compares the key features of a main charger and a dedicated parallel charger.
Table 1: Main charger and parallel charger feature comparison
As an example, a dual-charger system could be implemented with two bq25890 devices in parallel. These devices are in a 4mm x 4mm package. However, the second charger does not require many of the functions as shown in the table above. By using a bq25898C as the parallel (second) charger with smaller package, the total system cost and PCB space required can be reduced.
Consider using parallel charger when implementing fast charging into your design. This design consideration helps manage thermals when handling higher charge current, thus charging your devices faster and more efficiently. For more information about dual charger design, see the user’s guide for the bq25890 and bq25892.