The RSM series is a chip-format current-sensing resistor built around an all-metal resistor body of Manganin, Karma or Fe-Cr-Al alloy, joined to copper terminals by an electron-beam welded structure that the manufacturer states ensures high stability and reliability. The copper terminals carry a nickel under-plating with a tin top plating, the resistance value is applied by silk-screen marking, and the assembly is encapsulated in a high-temperature-resistant, insulating and flame-retardant resin that supports the all-metal structure's ultra-low resistance values while giving the part excellent weather resistance. Across the series, the RSM family carries ultra-low thermal EMF and ultra-low parasitic inductance, giving it a fast response suited to current-sensing applications, and all models follow the same derating curve, holding 100% of rated power up to 70°C ambient before linearly reducing to zero at 170°C.
The smaller chip sizes cover the lower end of the resistance range. The RSM1206 is rated at 2W and offers 1mΩ in Manganin at a TCR of ±150ppm/°C, 2-20mΩ in Manganin at ±75ppm/°C, and 6-25mΩ in Karma at ±75ppm/°C, with a thermal EMF of less than 3μV/°C. The RSM2010 is also rated at 2W and offers 0.5-1mΩ in Manganin at ±175ppm/°C, 2-7mΩ in Manganin at ±100ppm/°C, and 8-250mΩ in Karma at ±75ppm/°C. The RSM2512 is rated at 2W and spans 0.5-1mΩ and 1-4mΩ in Manganin, 3-4mΩ in Fe-Cr-Al and in Karma, and 5-50mΩ in Manganin, Fe-Cr-Al and Karma, with TCR values from ±25ppm/°C to ±150ppm/°C depending on material and value. The RSMB2512, sharing the same 2512 chip footprint, extends the range to 51-300mΩ in Karma or Fe-Cr-Al at ±50ppm/°C. The RSMP2512 is rated at 3W and covers a similar spread of 0.5-1mΩ and 1-2mΩ in Manganin, 3-4mΩ in Fe-Cr-Al and Karma, and 5-50mΩ in Fe-Cr-Al and Karma.
The larger chip sizes extend the series to higher power and resistance. The RSM2725 is rated at 4W and offers 0.2mΩ, 0.25mΩ and 0.5mΩ in Manganin at ±100ppm/°C, and 1mΩ through 3mΩ in Fe-Cr-Al at ±25ppm/°C. The RSM2728 covers 3-50mΩ in Fe-Cr-Al or Karma at 5W and 51-100mΩ in the same materials at 3W, both at ±50ppm/°C. The RSM2817 offers 1-3mΩ in Manganin at 5W and ±75ppm/°C, 4-50mΩ in Karma at 5W and ±50ppm/°C, and 51-100mΩ in Karma at 3W and ±50ppm/°C. The RSMB4527, the largest and highest-power model in the series, offers 0.5mΩ and 1mΩ in Manganin at 6W and ±150ppm/°C, 2-50mΩ in Karma at 6W and ±50ppm/°C, and 51-300mΩ in Karma at 4W and ±50ppm/°C. Chip outline dimensions and recommended pad sizes are specified individually for each model, and reel packing varies by chip size, from a 7-inch reel for 8mm tape at 5,000 pieces per reel for the RSM1206 up to a 7-inch reel for 25mm tape at 500-1,000 pieces per reel for the RSMB4527.
