Resistors keep cool onboard

Low-value resistors feature a novel open-air "flow-through" design that keeps the resistor's "hot spot" safely off the PC board and allows air to circulate around it.

New from TT Electronics Welwyn Components is the OARS Series of open-air current sense resistors.

The unique design of these low-value resistors solves a number thermal issues common in automotive and industrial electronics.

The series features a resistive element with a novel open-air "flow-through" design that keeps the resistor's "hot spot" safely off the PC board and allows air to circulate around it, contributing to cooler operations through increased heat dissipation.

As a surface mount device, the OARS Series resistors have compliant terminations that allow them to expand and contract with the PC board's thermal cycling, enabling them to meet or exceed the 1000 to 2000 cycles required by most automotive manufacturers.

This thermal cycling stresses the solder joints of conventional flat chip resistors, which can often cause failure.

The unique lead form of the OARS resistors provides an inherent advantage in compliance to the mechanical stress caused by thermal cycling.

The welded copper terminals in the OARS Series also provide a low-resistance terminal to enhance reliable performance for demanding applications.

The OARS Series resistors are rated for 1W at 85C (2W at 25C) with resistance values from 2 to 50mohm with tolerances down to +1%.

They feature TCRs as low as +20ppm/C and inductance values in the single-digit nanohenry range.

Operating range is -40 to +125C.

The company has also developed a wider version with a higher power rating than conventional metal element resistive devices.

Designated the OARS-XP Series, the resistor features a wider metal alloy resistive element that offers exceptional TCR ratings and superior thermal compliance.

The resistors unique form factor provides designers with several advantages.

The wider resistive element enables higher current to pass through the device and the open-air design provides a far cooler operation by allowing more air flow under the resistive element to keep heat from being transmitted to the PC board.

In addition, the distinctive form of the product provides the inherent ability to flex slightly and provide stress relief during extreme temperature cycling on FR4 or metal substrates.

Resistance values for the OARS-XP Series range from 2mohm to 50mohm, with standard tolerances of +1% and +5%.

Inductance values are less than 10nH, with operating temperature ranges from -40 to +125C.

All OARS series parts are RoHS compliant and zero ohm jumper versions are also available.

The OARS Series also features bimetallic construction with welded copper terminals that aid solderability and resistance measurement reliability.

Applications include automotive motor control, power supply and process monitoring.

John Graham, Marketing and Sales Director, said: "TT electronics' investment in the OARS Series provides design engineers with a power current sense resistor in surface mount format with enhanced thermal characteristics".

"The OARS devices are extremely rugged, with the ability to handle surge currents far higher than conventional resistors and because there are no organic materials used in their construction, the OARS resistors are inherently flameproof - an important consideration in many applications".

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