Newly Developed Compact GMR50 Current Detection Chip Resistor (Shunt Resistor) with High Rated Power : Industry-Highest 4W Rated Power from 5.0×2.5 mm Device

ROHM recently announced the development of the GMR50 current detection chip resistor (shunt resistor), which assures an industry-leading rated power of 4 W from a device with a diminutive 5.0×2.5 mm size.
*ROHM survey, November 28, 2019

About Current Detection Resistors (Shunt Resistors)

Current detection resistors (shunt resistors) are resistors that are used to detect current; current detection resistors and shunt resistors are basically used in the same way. Conventional shunt resistors have been called current-dividing resistors that are inserted in parallel in an ammeter, but resistors inserted in series into a current path and rely on Ohm’s laws to determine the current value from the voltage drop that occurs across the resistor are also called shunt resistors. They are used for current detection in various motors and power supply circuits, and are components that are also often used in the power supply circuits and power conversion circuits within the DC-DC converters, AC-DC converters, and power devices that are described on Tech Web.

When current values are large, in general current detection resistors with a low resistance value in the range of milliohms to hundreds of milliohms are used. This is because, due to the fact that a voltage drop is used, the voltage drop when for example a 5 A current is flowing through a 10 Ω resistor is 50 V, and this is difficult to handle for a circuit that runs on 5 V and 12 V voltages. If the resistor is 100 mΩ, the voltage drop for a 5 A current is 500 mV, which can easily be handled by a low-voltage circuit. The resistor value is selected according to the current to be detected and the voltage drop, but it is also necessary to consider that a voltage drop is effectively a loss of power.

Another matter for study is the rated power. These components are premised on the use of a voltage drop across the resistor, and so the power loss in the resistor is determined simply by the resistance value and the current flowing. The rated power is indicated in the specifications for the resistor, and so a device with a rated power compatible with the conditions of use should be selected. In general, when the rated power is higher, the size of the resistor tends to be larger. However, demands for reduced equipment sizes in recent years have led to requests for current detection resistors that are small in size but have a high rated power.

When using a current detection resistor, the resistance value, rated current, and size are all important parameters for study; in addition, precision (tolerance) and the temperature coefficient must also be considered.?

Features of the GMR50 Current Detection Resistor

• ・Industry-high rated power of 4 W (pin temperature TK=90°C) secured for a device of size 5.0×2.5 mm
• ・Enhanced heat dissipation to substrate through reexamination of electrode structure and optimization of device design
• ・Footprint reduced by 39% compared with other components rated at 4 W
• ・Highly durable with respect to overcurrent loads
• ・Stabilized current detection precision can be maintained even when a load exceeds the rated power
• ・Excellent temperature coefficient of resistance even for low resistance values

Dramatic Boost in Heat Dissipation Performance to Achieve Industry-High Rated Power

In order to raise the rated power of a current detection resistor and also reduce the physical size, long-term reliability with respect to temperature increases of the resistor must be ensured. The GMR50 achieves dramatically improved heat dissipation performance through a reexamination of the electrode structure and optimization of the device design. For example, when a 5 mΩ component is used at 2 W, the rise in surface temperature can be reduced by 57% compared with general 5025 size components.

Compact Space Savings Even at High Rated Power

The GMR50, even with its compact 5.0×2.5 mm size, ensures an industry-high 4 W rated power at a pin temperature of TK=90°C, and a rated power of 3 W when the pin temperature is TK=110°C. The device is a size smaller than conventional 4 W components, for space savings that include a 39% reduction in footprint.

Excellent Durability Makes Possible Stable Current Detection

Ideally, a current detection resistor should be capable of stable current detection even when large currents flow due for example to short-circuits to the power supply or to ground. The GMR50 affords excellent heat dissipation, and so the durability of the product with respect to overcurrent loads is high compared with other such devices, and even when an overcurrent exceeding the rated value flows there is little change in the resistance value, so that stable current detection precision can be maintained.

Excellent Temperature Coefficient of Resistance Achieved Even at Low Resistances

By adopting a highly functional alloy material as the resistive body metal, the GMR50 achieves an excellent temperature coefficient of resistance (TCR) of between 0 and +25 ppm/°C at the low resistance value of 5 mΩ. Thus the effect of ambient temperature changes is minimized, and stable and precise current detection is made possible.

Support for Thermal Simulations

ROHM is strengthening design support for thermal simulations and the like. Through advance estimation of the rise in temperature when substituting the GMR50 for a currently used component, design do-overs can be reduced, and development time can be shortened.

For example, it can be confirmed that, in a circuit in which two conventional components (size 5025) had to be used in parallel, a single GMR50 is sufficient to suppress rises in surface temperature more effectively. Thermal design can also be supported through simulations that include power supply ICs, SiC MOSFETs, IGBTs, and other peripheral components in addition to resistors. Thus ROHM, as a diversified semiconductor manufacturer, provides a comprehensive design solution.

Lineup

The following summarizes the GMR50, a new product 5.0×2.5 mm in size; the GMR100, another product in this lineup, 6.4×3.2 mm in size; and the GMR320, which is currently in development.

Part No.	Size Abbr. (mm) <inch>	Rated Power	Resistance Tolerance	Resistance Temp Coefficient TCR (ppm/℃)*1	Resistance Range （mΩ）	Operating Temp Range （℃）
GMR50	5025 <2010>	3W<110℃> 4W<90℃>	F （±1%）	0 to ＋25	5	－55 to ＋170 ★－65 to ＋170
				±25	10 to 220 （E24 series）*2
GMR100	6432 <2512>	3W<110℃> ★ 5W<110℃> ★ 7W<70℃>		0 to ＋25	5
				±20	10 to 220 （E24 series）*2
☆ GMR320	7142 <2817>	7W<110℃> 10W<70℃>		0 to ＋25	5
				±25	10 to 100 （E24 series）*2

☆ : Under development (Development schedule will vary somewhat depending on the resistance value; please inquire for details)?
★ : Under study
*1 : ＋20℃ to ＋60℃
*2 : Development schedule will vary somewhat depending on the resistance value; please inquire for details.

• Web page devoted to chip current detection resistors (shunt resistors)