High power current sense resistor

07 December 2010

Chip resistor delivers 3W power rating and 0.003O resistance values in 1225 size
Chip resistor delivers 3W power rating and 0.003O resistance values in 1225 size

Chip resistor delivers 3W power rating and 0.003O resistance values in 1225 size.

Providing aerospace and military electronics design engineers with a compact high power current sense resistor capable of precision current measurements at ultralow resistance values, TT Electronics’ IRC has developed a series of high-reliability thick film chip resistors tested to MIL-PRF-55342-level specifications.

Designated the LRF3W-MIL Series, the resistors are terminated on the long sides of the 1225-size chip package to provide the maximum thermal transport path, which gives the resistors their high current-handling capability, and improves their overall reliability.

“We’ve seen an increasing demand for our current sense resistors, especially in high-reliability applications in military and space-based electronics systems,” said Gary Bleasdell, Director of TT electronics’ IRC’s thick film business unit. “By developing our LRF3W Series resistors to meet the demanding requirements of MIL-PRF-55342, we’ve been able to provide our customers with a robust thick film current sense resistor capable of handling up to 3 watts at 70°C in a chip size that is normally limited to 1 watt. This provides a significant reduction in board footprint and overall weight, both of which are critical for space applications.”

According to Bleasdell, a key feature of the resistor’s design is the long-side termination, which provides a shorter signal path as well as a wider termination contact with the traces on the PC board layout pads. Increasing the PC board copper land pad area to (900mm2) on each side of the chip gives the resistor the ability to handle 3 watts of power at 70°C.

The LRF3W-MIL Series resistors employ a high-reliability thick film resistive element on a high purity alumina substrate with nickel barrier layers on copper-plated wraparound terminations and a protective overcoat to ensure stability in harsh environments. Standard Sn/Pb terminations, as well as lead-free (matte Sn) terminations are available.

Resistance values for the LRF3W-MIL Series range from 0.003Ω to 1.0Ω, with tolerances available down to ±1% and TCRs to ±100ppm/°C. Operating temperature range is from -55°C to +150°C.

The resistors can be screened to MIL-PRF-55342, NASA EE-INST-002, or customer source control drawing to meet special application requirements.

Typical lead-time for the LRF3W-MIL Series resistors is 14 weeks if stock is not available.

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