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© eskymaks dreamstime.com Business | October 24, 2012

VPG's foil resistors successful in Precision Analog applications

An increasing number of semiconductor companies are recommending its VPG's Vishay Foil Resistors (VFR) brand resistors as part of their reference designs for precision analog applications.
In the latest example, Intersil Corporation is using VFR's (Vishay Precision Group, Inc.) ultra-high-precision FRSM Z1-Foil wrap-around chip resistors to maintain exceptional gain accuracy under extraordinary thermal and environmental stresses in its new precision, low-noise signal chain solution.

Included in Intersil's signal chain solution are the 40 V ISL28617 low-noise instrumentation amplifier, the ISL21090 low-noise voltage reference, and the ISL26134 low-noise 24-bit delta-sigma analog-to-digital converter (ADC). The ISL28617 offers excellent gain accuracy and gain temperature coefficient over a temperature range of -40°C to +125°C, with the industry's highest common mode rejection ratio (CMRR) in all gain configurations. The ISL28617 can provide both high gain and attenuation, and is ideal for instrumentation, industrial, motor control, and medical systems.

The gain of the ISL28617 can be programmed from 0.1 to 10,000 via two external resistors. Since gain accuracy is determined by the matching of the resistors, resistor temperature drift and instability create gain errors and ultimately limit system accuracy. For high gains where the resistors are subject to different voltages, resistor voltage coefficients and unequal self-heating can add additional errors. To maintain gain accuracy, resistors with low temperature coefficient of resistance (TCR) and power coefficient of resistance (PCR) are required.

To reduce gain error due to thermal gradients in Intersil's signal chain solution, the FRSM series offers low typical TCR of ±0.05 ppm/°C from 0°C to +60°C and ±0.2 ppm/°C from -55°C to +125°C, +25°C ref, and low PCR of 5 ppm at rated power. For increased reliability, the devices provide exceptional load-life stability of ±0.0025% (25 ppm) at 70°C and rated power for 2,000 hours and ±0.005% for 10,000 hours, and tight tolerances to ±0.01%. The resistors feature 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/V of applied voltage (<-40 dB), and a voltage coefficient of <0.1 ppm/V.

Additionally, Xilinx is using VFR ultra-precision CSM current-sensing resistors in its FPGA circuit to measure the amount of current handled by the design.

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