Vishay Precision Group, Inc. (NYSE: VPG) today announced that it has completed tests showing that its Bulk Metal ® Foil current sensing resistors meet the accuracy and stability required by its aircraft customers for charging of Li-ion batteries in avionics applications. VFR resistors provide a variety of device configurations and ultra-high-precision specifications to help ensure the efficient and safe charging of Li-ion batteries. They include the surface-mount Z-Foil VCS1610Z and VCS1625ZP and the high-power VCS331Z and CSNG (offering 3- or 6-chip constructions). The Li-ion battery charging process goes through several critical phases to ensure the battery is charged to its maximum capacity, while at the same time following certain safety rules to avoid explosion or fire. Li-ion battery chargers require accurate current and voltage settings and monitoring, as well as a constant current and constant voltage. If these accuracy requirements are not met, the charger will undercharge or overcharge the battery. A failure to completely charge the battery results in reduced battery life, while overcharging can cause batteries to fail due to overheating. Precision current sensing resistors are required to charge and monitor the Li-ion battery at a known current level until it reaches its final voltage. At this point, the charger circuitry switches over to constant voltage mode, providing the current necessary to hold the battery at this final voltage. For both phases, Bulk Metal Foil resistors provide higher accuracy than other technologies, such as thin film, thick film, and wirewound resistors. “Li-ion batteries are well established in portable consumer electronics and are now becoming more popular in military and advanced civilian avionics. As the scope of their applications has expanded, so have the stringent requirements they must meet, especially in terms of cell safety and lifetime. For designers, the main challenge in meeting these requirements is in finding the optimal point between undercharging and overcharging through continuous accurate and stable monitoring of input and output current,” said Yuval Hernik, senior director of application engineering for VFR.