VPG's New Foil and Z-Foil 2-, 3-, and 4-Resistor Voltage Dividers and Resistor Networks Feature TCR Tracking to ±0.1 ppm/°C and Matching Tolerance to ±0.005%

The resistor arrays come in standard configurations, but with custom values and tolerances for all thirteen possible schematic variations of 2, 3, and 4 resistors. For applications requiring maximum precision, the Z-Foil devices feature low absolute 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., TCR tracking to ±0.1 ppm/°C, matching tolerance to 0.005 % (50 ppm), and PCR (ΔR due to self heating) of 5 ppm at rated power.



The unitized resistor networks announced today are comprised of 2, 3, or 4 VPG resistor elements combined and molded into single units to provide several advantages in applications demanding maximized performance. These resistor arrays featuring Z-Foil technology provide a significant reduction of the resistive components' sensitivity to ambient temperature variation (TCR) and applied power changes (PCR). The devices' low TCR minimizes errors due to temperature gradients, allowing designers to guarantee a high degree of stability and accuracy in fixed-resistor applications.



The Z-Foil arrays are designed and manufactured to eliminate the inter-parameter compromise inherent in all other types of precision resistors. All important characteristics — tolerance, long-term shelf life and load stability, temperature coefficient, noise, capacitance, and inductance — are optimum, approaching the theoretical ideal in total performance.



For a low thermal EMF of 0.05 μV/°C, the leads that emerge from the arrays' packages connect directly to the resistance elements, or an internal PC board. In addition, each element offers a wide resistance range from 1 Ω to 100 kΩ, and can be combined for even higher values. Finally, the elements retain all the advantages of discrete Bulk Metal Z-Foil resistors, plus the ability to be further sorted for TCR track and absolute matching before encapsulation.



The Z-Foil resistor arrays feature power ratings of 0.3 W per element at +125°C and resistance ratio stability to 0.001% at 0.05 W. The resistor networks 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/V of applied voltage (<-40 dB), a voltage coefficient of <0.1 ppm/V, and a non-inductive (<0.08 μH), non-capacitive design.



The networks are optimized as voltage dividers, bridges, and attenuators in a wide range of military and aerospace, medical, and high-temperature down-hole applications where performance and stability are important, including differential amplifiers, gain-defining resistors in digital voltmeters, ratio arms in bridge circuits, fuel metering and fire control instrumentation, binary ladders, and linear and linear-summing networks.



For applications that require only near-maximum stability, the standard foil resistor arrays feature a TCR of ±2 ppm/°C from -55°C to +125°C, +25°C ref., TCR tracking to ±0.5 ppm/°C, and matching tolerance to 0.005 % (50 ppm). The devices offer a low thermal EMF of 0.05 μV/°C and a wide resistance range from 1 Ω to 150 kΩ. The standard foil resistor arrays feature power ratings of 0.3 W at +125°C for resistance values to 100 kΩ, and 0.2 W for resistance values >100 kΩ.



Four fundamental factors determine how ideal a precision divider resistor will be: initial individual resistor tolerance; initial ratio tolerances among resistors of different values as well as like values; the degree to which the array holds all absolute and ratio tolerances through all encountered operating conditions; and fast frequency response and thermal stabilization time for high-speed circuits. Until the development of foil resistors, precise control of all four factors in the same resistor technology was virtually impossible.



The stability of Vishay Foil resistors allows designers to eliminate other passive components and costly corrective circuitry that are needed primarily just to compensate for the inadequacies of other resistor technologies. With user-specified values in standard configurations, only a minimal shift in resistance value will occur during the devices' entire lifetime. Most of this shift takes place during the first few hundred hours of operation, and virtually no change is noted thereafter.



The superiority of Bulk Metal Foil technology over other resistor technologies — such as thin film and thick film technologies — when subjected to ESD (electrostatic discharge) is attributed mainly to alloy uniformity and/or the much higher thickness and therefore greater energy capacity of the foil resistive element. Vishay Foil resistors can withstand ESD of at least 25,000 V, while thin film chip resistors can undergo catastrophic failures from electrostatic discharges as low as 3,000 V.



Offered with terminations plated with lead (Pb)-free or tin/lead alloys, samples and production quantities of the 2-, 3-, or 4-resistor arrays are available now, with lead times of six weeks for standard orders.