The HTH series is based on VFR's next-generation Z1-Foil technology, which provides an order of magnitude reduction in the Bulk Metal Foil element's sensitivity to temperature changes — both external and internal — while providing long-term stability in high-temperature environments. HTH devices offer TCR of ±1 ppm/°C from -55°C to +125°C and ±2.5 ppm/°C from -55°C to +220°C, +25°C ref. The resistors feature exceptional load-life stability to ±0.05% at +220°C for 2,000 hours at working power, long-term stability to ±0.05% at +240°C for 2,000 hours (no power), and tight tolerances to ±0.02%. The devices are capable of withstanding electrostatic discharges at least to 25 kV without degradation.
The HTH series is offered in 5x5, 15x5, and 15x10 chip sizes, in addition to six case sizes ranging from 0603 to 2512. The devices feature two different chip design layouts according to their size. The HTH series devices provide a wide resistance range from 10 Ω to 125 kΩ, with any resistance value within this range available at any tolerance with no additional cost or lead time effect. 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 per volt of applied voltage (<-40 dB), and a voltage coefficient of <0.1 ppm/V.
Relatively few of today's passive components are rated for such high-temperature operation, and even when they are, their useful operating life may only be a matter of hours or days. The HTH series is optimized for a wide variety of demanding high-temperature applications, including geothermal measuring equipment, turbine engine control, and environmental test chambers in military, industrial, automotive, and down-hole drilling systems. The Z1-Foil technology allows VFR to produce customer-oriented products designed to satisfy unique and specific technical requirements. In addition to the special chip stabilization under extreme environment conditions in the production line, additional specially oriented post-manufacturing operations (PMO) are offered for high-temperature applications that require an even higher degree of reliability and stability.
In high-temperature applications, the most important factors are the end-of-life tolerance, which is part of the stability, and, to a lesser extent, the initial tolerance, said Yuval Hernik, senior director of application engineering for Vishay Foil Resistors. Changes in the ambient temperature, heat from adjacent components, destabilizing thermal shocks from suddenly applied power, long-term exposure to applied power, and the repetitive stresses from being switched on and off in environments with temperatures above +175°C all can affect stability. For high-temperature applications where stability and the total error budget are the main concerns, this new generation of Vishay Foil resistors addresses all of these parameters and offers the best resilience over time and temperature.
The key to stability and reliability is to keep circuits cool, and unfortunately, in extreme-temperature applications such as down-hole electronics, that is not always an option. Vishay Foil resistors are known to exhibit very low aging and thus can achieve reasonable end-of-life tolerance (or total error budget) even at high temperatures. In applications that require stability under extreme environments, the short-term cost savings of using a thick or thin film resistor may easily be lost due to field failures and time spent on calibration. That's why the marginally higher cost of Vishay Foil resistors often represents the best investment a designer can make.
Samples and production quantities of the HTH series are available now, with lead times of five weeks for samples and eight weeks for standard orders.