ROHM’s New Thick Film Shunt Resistors

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ROHM has developed thick-film shunt resistors, LTR100L, optimized for industrial and consumer applications. Often used to detect current in battery protection and motor drive circuits, shunt resistors require higher accuracy to improve reliability and ensure high efficiency operation.

Recent years have seen an emphasis on energy savings in the industrial and consumer fields, with efforts being made to reduce power consumption during drive operation by using motor inverters. At the same time, protection circuits are becoming more important in these fields as applications continue to increase in power.

ROHM has been working on expanding its considerable lineup, most recently with the GMR320 series of metal plate shunt resistors – released in February 2021. The devices feature a higher guaranteed rated power of up to 10W. Since April 2018, ROHM has been producing the LTR50 series of low ohmic thick film shunt resistors rated at 2W. With these latest products, ROHM has expanded its lineup of thick-film shunt resistors to support an even higher power area.

The LTR100L series achieves the industry’s highest rated power of 4W in the 3264 size (3.2mm × 6.4mm) / 1225 size (0.12inch × 0.25inch) by revising resistor materials and applying terminal temperature derating. This makes them ideal for current detection in motor control and overcurrent protection circuits for industrial and consumer applications, which are progressing towards higher power. In addition, optimization of the element structure delivers best-in-class TCR (temperature coefficient of resistance) characteristics among thick-film shunt resistors. As a result, they are not easily affected by temperature – enabling high accuracy, high reliability current detection.

Samples can be purchased from one piece from online distributors Digi-Key, Mouser, and Farnell (starting with samples that have the following resistances: 10mΩ, 47mΩ, and 91mΩ).  Furthermore, a variety of content and tools useful for design, such as application notes, are available on ROHM’s website. Simulation Models will also be released.

Going forward, ROHM will continue to expand its resistor (a founding product) lineup from low to high power. The core aims:  achieving greater energy savings and reliability, while contributing to the evolution of industrial and consumer equipment by leveraging its strengths as a comprehensive semiconductor manufacturer – to provide solution proposals utilizing ICs and discrete products.

Key Features

  1. Achieves the industry’s highest 4W rated power for thick-film shunt resistors in the 3264 size (1225 size in inches)

ROHM’s new products adopt a high heat dissipation wide terminal package. In addition, optimizing resistor materials and applying terminal temperature derating allows ROHM to achieve thick film shunt resistors with the industry’s highest rated power of 4W in the 3264 size (3.2mm × 6.4mm) / 1225 size (0.12inch × 0.25inch). This is about twice that of conventional products in the same size – making them ideal for current detection in motor control and overcurrent protection circuits for industrial and consumer applications where higher power is required.

  1. Superior temperature coefficient of resistance contributes to greater application reliability

The LTR100L series achieves excellent TCR characteristics of less than 300ppm/℃ (at 10mΩ resistance value products) within the operating temperature range through an optimized element structure. This reduces the change in resistance value due to temperature changes compared with standard products by 50% to 65%, – enabling high accuracy current detection that improves application reliability.

Tools that significantly reduce design load

In November 2021, ROHM launched a web-based simulation environment that enables thermal simulation of shunt resistors in combination with power devices and ICs on its website (starting with the PSR series). These simulations allow thermal design – an issue during application design – to be simulated in advance, reducing design load. ROHM also offers current detection solutions utilizing ICs along with discrete components that contribute to greater circuit efficiency and miniaturization. As an example, for motor drive circuits that require current detection for overcurrent protection and control, adopting ROHM’s class-leading low noise operational amplifiers together with shunt resistors results in high accuracy current detection.

Thick-Film Shunt Resistors: LTR Series Lineup

The LTR100L series utilizes a thick-film structure that makes it relatively easy to expand the resistance value range.


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