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
Dramatic Boost in Heat Dissipation Performance to Achieve Industry-High Rated Power
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
Excellent Temperature Coefficient of Resistance Achieved Even at Low Resistances
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.
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.
|0 to ＋25||5||－55
|±25||10 to 220
|0 to ＋25||5|
|±20||10 to 220
|0 to ＋25||5|
|±25||10 to 100
☆ : 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.