Avionic & military applications need -55°C operation

Overview
The commercial-off-the-shelf (COTS) initiative of 1994 significantly shook up the military IC industry. In conjunction with improvements in semiconductor vendor IC reliability, no longer were /883 or JAN qualified ICs required. The military was allowed to integrate commercial and industrial grade ICs into their weapons systems. This trend freed designers of military and avionics (electronics for aircraft) systems to newly scour the portfolios of various semiconductor IC companies who did not necessarily specialize in military grade parts, or look into other portions of the IC portfolios of those companies that previously did. The benefits of COTS have included reduced system development & maintenance time and costs.

However, the requirements for many of these systems are still very stringent. For example, commercial aircraft and unmanned aerial vehicles (UAV) that soar at altitudes in excess of 30,000 feet encounter temperatures approaching -50°C or worse. Therefore, industrial (down to -40°C) and commercial (down to 0°C) temperature-rated ICs would not suffice. Some key applications include outside cabin-mounted environmental sensors (air speed, temperature, humidity, etc.), flight control computers, infrared image sensors and cockpit voice recorders.

With ongoing assault against terrorism and the desire to continually protect armed forces on the ground, in the sea and in the air, there has been an increase in safer first-strike capability technology as well as predictive and defense counter-measures technology.

Important applications in this area include:
•   Integrated defensive electronic countermeasures (IDECM)
•   Sophisticated fighter aircraft such as the joint strike fighter (JSF)
•   Joint-air-to-ground missiles (JGAM)
•   Joint direct attack munitions (JDAM) smart bombs with their GPS-embedded modular (GEMS) inertial guidance systems
•   Various radar jamming systems.

Once again, a military temperature range IC is required in these applications due to the wide temperature variation of their deployment environment.

Many ground-based military applications (some battery-powered) such as soldier man-packs, radar systems, joint tactical radio systems (JTRS), armored vehicles and night vision apparatus also require ICs that operate across hot-to-cold temperature extremes from a high of 125°C down to -55°C since they can be placed almost anywhere, and further in humid or arid environmental conditions.

Challenges for ICs at harsh cold temperatures
Ambient temperature extremes may cause parametric, and, in some cases, catastrophic problems for ICs. Hot temperature issues including electromigration, parametric drift, parasitic leakage, hot spots and high power dissipation traditionally have been identified and dealt with through improved design and layout techniques by designers.

On the other hand, cold temperature issues for ICs are coming more to the forefront thanks to adoption in applications for the military and avionics market segments. For example, at altitudes above 30,000 feet - where most commercial aircraft fly - temperatures approach a frigid -55°C. Furthermore, in addition to IC parametric drift, designers must deal with board leakage/condensation potentially causing trace shorting, thermal shock if rapid changes from cold to hot occur, low temperature oscillations, instability, overshoot and poor filter performance. IC designs at cold temperature must carefully compensate for these factors.

The use of low dropout (LDO) linear regulators is commonplace in both non-portable and handheld electronic systems. Improved specifications, reliability and protection features are enticing system designers to consider them in harsh environments too. For example, lower dropout voltages enable higher efficiency conversion, paralleling regulators spreads heat and reduces hot spots on PCBs, while lower input-to-output voltage differentials open up the types of system rails to be powered. Further, low quiescent currents increase battery run time, higher input voltage specifications protect against system voltage transients, reverse input/output and reverse current protection shield the IC and the surrounding electronics thereby increasing robustness, low output voltage noise minimizes system EMI concerns, and compact thermally-enhanced packaging drives heat out of systems more effectively. These features, in addition to their design simplicity, have allowed LDOs to occupy 1A-5A application spaces that were previously solely serviced by switching regulators.