In the world of modern electronics, smartwatches represent a marvel of intricate engineering.
These compact devices encapsulate a multitude of components within a small structure designed to comfortably fit on a human wrist. This intricate design process involves a myriad of meticulous decisions and innovative engineering solutions. A great example of this is the use of Littelfuse’s eFuse to meet the circuit protection requirements for the wireless charger of a smartwatch.
Engineers at Littelfuse were tasked with providing protection from overvoltages, overcurrents, and high temperatures.
An initial solution, which involved the use of a fuse, Zener diode, temperature sensors, and control ICs, was deemed unsuitable due to the limited board space. The team thus decided to explore the possibility of using an electronic fuse IC that integrates all these functions.
The smartwatch manufacturer evaluated several e-fuses, but found their output voltage was limited to 12 V, which was insufficient for the required 20 V @ 5 A. The solution emerged in the form of Littelfuse’s LS0505EVD22 Series eFuse, a component of the company’s eFuse series launched last October. These eFuse ICs offer a broad range of power inputs (3.3V to 28V) and integrated protection.
The LS0505EVD22 eFuse not only provides overvoltage protection but also safeguards against overcurrent, short circuit, inrush current, reverse current, and overtemperature events with real-time diagnostics—all within a single chip. This electronic fuse (eFuse) IC adheres to the requirements of the USB Type-C power delivery standard in portable devices. It can safely withstand 100 W of power and remains undamaged even if the Type-C power delivery adapter supplies 20 V and 5 A.
The LS0505EVD22 eFuse’s output is controlled by a series MOSFET with a low 50 mΩ RDS(ON), which reduces the IC’s power loss and temperature rise. Test data show that the IC’s temperature only rises by 37° C when operating at 5V @ 1 A for 20 minutes with an input short.
The eFuse IC also has additional features such as overvoltage protection provided by a parallel MOSFET and overcurrent protection by a current limit block. It also has a soft start function that controls the rise time of the output to prevent potentially hazardous overshoots. The 30 V rating of this eFuse is superior to that of competitive products in the market.
The compact design of the eFuse IC package, a space-saving DFN2X2_8L Package, makes it ideal for use in portable devices. The eFuse also offers flexibility for future designs with 5 V and 3 A output, saving the smartwatch design team both time and cost as there is no need to select and qualify a new component.
Beyond smartwatches, this versatile eFuse can be used in other products such as tablet PCs, Bluetooth headsets, PCs/notebooks, datacom power systems, storage devices, and other applications involving electronics and computers.
In conclusion, Littelfuse’s eFuse is an excellent example of how innovative engineering can solve complex design challenges in the electronics industry. Its integration into smartwatches underscores its versatility and efficiency in ensuring circuit protection for compact devices.
