Ultra-High-Precision Resistors


Ultra-High-Precision Resistors

Ultra High Precision Resistors

Vishay Precision Group, Inc. announced that its Vishay Foil Resistors division (VFR) is now offering a wide variety of surface-mount and through-hole resistors built on Bulk Metal® Z- and Z1-Foil technologies for high reliability and high stability in medical applications. Including the recently introduced CSM3637Z, CSM3637P, Z203 and FRSM series, a wide variety of resistor configurations, chip packages, and ultra-high-precision specifications are available for optimized performance.

Devices such as the VCS1625Z, VCS1625ZP and CSM3637Z offer 4-terminal Kelvin connections for high reliability, while the FRSM, VSMP and FRSH series feature wraparound terminations. The flexible terminations of the SMR3DZ and SMR3D eliminate stress transference from the PCB due to a difference in thermal coefficient of expansion (TCE), while the hermetically sealed packages of the VHP101, VHA512Z, and VSM46 (PRND) prevent the ingress of moisture and oxygen.

“Performance, long-term stability, precise control, and safety are critical factors for every medical application,” said Yuval Hernik, senior director of application engineering for Vishay Foil Resistors. “When selecting a precision resistor, it is essential for designers to understand the specifications and requirements that are of particular importance to their applications and their effect on system performance. VFR’s long track record of success in medical applications and its long-term commitment to the medical and military markets, which share a significant overlap, have made Bulk Metal Foil the preferred resistor for a wide range of medical applications.”

The stability of a resistor depends primarily on its temperature, which is affected by temperature coefficient of resistance (TCR) and power TCR (ΔR due to self-heating). These performance characteristics are particularly important in medical instrumentation and equipment, where Bulk Metal Foil resistors deliver proven reliability and stable performance, even when exposed to unstable levels of temperature and humidity or other harsh environmental conditions. Other important design considerations in medical equipment include providing immunity to single-event upsets in electronics, such as radiation from oncology equipment, and damage caused by electrostatic discharge (ESD).

“The accuracy (precision) of any resistor at a given time usually has little relation to its initial tolerance as listed in datasheets,” Hernik added. “Purchased tolerance, in fact, is an invalid single measure of precision beyond the resistors’ first few hours of service life, since the effects of storage, assembly, load and environment stress can change a 0.05% resistor very quickly into a 0.1% or even 1% resistor.”

VFR resistors provide several industry-leading features that translate into ultra-high accuracy. These include long-term load-life stability down to ±0.0025% at 70°C for 2,000 hours; TCR down to ±0.05 ppm/°C (from 0 °C to +60 °C) and ±0.2 ppm/°C (from -55°C to +125°C, +25°C ref.); power TCR (ΔR due to self-heating) of 5 ppm at rated power; and tight tolerances to ±0.01 %. Featuring a non-inductive (< 0.08 μH), non-capacitive design, the devices offer a rise time of 1.0 ns, with effectively no ringing, a thermal stabilization time of < 1 s (nominal value achieved within 10 ppm of steady state value), current noise of 0.010 µVrms per volt of applied voltage (< -40 dB), and voltage coefficient of < 0.1 ppm/V. Bulk Metal Foil resistors are immune to damage from radiation and withstand ESD spikes at least to 25 kV. The devices provide a wide range of resistance values, with any resistance value within their given range available at any tolerance with no additional cost or lead time effect.

Typical applications for the resistors include DC/DC converters, feedback circuits, and precision amplifiers in a wide range of medical devices, such as cardiac mapping systems, furnace control units, 3D imaging, X-ray generators for CT systems, motor-driven equipment, intravascular cooling systems, ultra-sonic microscopes, and much more.

Samples and production quantities of the foil resistors are available now, with lead times of five days for prototype samples and from two days to five weeks for standard orders from VFR’s stocking distributors.

Further information about Vishay Foil Resistors products is available at http://www.vishayfoilresistors.com. Follow Vishay Foil Resistors at http://twitter.com/VPGFoil.


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