Resistors directly replace wirewound & metal film devices

The VTA57Z features ultra-low TCR of ±0.05 ppm/°C nominal (0°C to +60°C) and ±0.2 ppm/°C nominal (-55°C to +125°C, +25°C ref.), and load-life stability of less than ±0.005% after 2,000 hours of rated power at 70°C. Tested to EEE-INST-002 guidelines for critical space applications, the VTA57Z offers high power ratings of 0.25 W at +70°C and a 160 V maximum working voltage. The device features a wide resistance range from 5 Ω to 100 kΩ, with tight resistance tolerance to ±0.01%. Any conceivable ohmic value within this range, to six digits, is available with no additional cost or lead time effect.

Compared with wirewound and metal film resistors, Bulk Metal Foil resistors operate at higher frequencies with higher speed, lower inductance, lower capacitance, and smaller phase angles, in addition to providing higher power density, lower TCR, better load-life stability, and lower current noise. Harmonic distortion is another important consideration in the choice of precision resistors for precision applications because a significant signal voltage may change the resistance value. Under these conditions, Bulk Metal Foil resistors behave more linearly than other resistor technologies. Foil resistors are available in both axial-lead and chip configurations, and they can be switched from one to the other with no electrical redesign required. Wirewound devices, by contrast, are not available in the chip format used in most assembly processes.

"Another disadvantage of wirewound devices is that TCR tracking is especially difficult with resistors of unequal values," said Yuval Hernik, senior director of application engineering for VFR. "For an extra cost, the same values can be selected for TCR tracking, but the devices must be packaged and handled with extreme care to avoid mixing. In addition, as resistance values diverge, values of minimal divergence require different wire lengths while values of greater divergence require different body sizes or wire diameters. Therefore, these components respond differently through almost all other performance criteria, with consequent deterioration of ratios in other critical areas, such as load life and temperature cycling. Foil resistors, on the other hand, have the same inherently low TCR for all values above 100 Ω and track better than wirewound devices, without the associated selection, packaging, and handling costs."

Featuring a non-inductive (<0.08 μH), non-capacitive design, the VTA57Z offers a rise time of 1.0 ns with effectively no ringing, a thermal stabilization time of <1 s (within 10 ppm of steady state value), maximum thermal EMF of 0.1 μV/°C, and voltage coefficient of <0.1 ppm/V. The resistor withstands ESD spikes to at least 25 kV and is available with both lead (Pb)-free and tin/lead alloy terminal finishes.

Samples and production quantities of the new Bulk Metal Foil resistor are available now, with lead times of five working days for prototype samples and eight weeks for standard orders.