New Current-Sensor ICs Check the Pulse of Power Electronics

Oct. 13, 2023

Can current-sensor ICs win out against the shunt resistor and other venerable passive components? Check out some of the latest offerings on the market in this Products of the Week gallery.

James Morra

Related To: Electronic Design

Isolated Current-Sensor ICs Rise to Challenge of High Currents

As current levels increase in industrial- and automotive-grade power systems—typically to more than 200 A and often up to 2,000 A—it’s becoming even more of a challenge to monitor them accurately.

Crocus Technology claims that its CT45x family of isolated current-sensor ICs can solve the challenges of high currents without what it calls the complexities of current-sense resistors or the compromises of Hall-based current sensors.

Like AMR current sensors, the CT45x can sense slight changes in electrical resistance under the influence of external magnetic fields (due to so-called “magnetoresistance"). The variations in resistance are then used to accurately sense the amount of current traveling through it, with lesser amounts of resistance signaling the presence of large currents, and vice versa. Crocus said TMR-based current sensors are unique in that they use the peculiarities of quantum physics to enable higher sensitivity, less noise, and more stable performance over a temperature range.

TMR current sensors also have common-mode field rejection to cancel out stray magnetic fields without bulky shielding that’s sometimes required with existing Hall-based current sensors. But unlike these current sensors, Crocus said its TMR technology can also remove the need for costly concentrators—also called magnetic cores that magnify voltage signals in cases where high currents are present—and even cores.

The contactless current sensor ICs support a sampling frequency of up to 1 MHz to capture rapid fluctuations in AC or DC current with high precision, enabling real-time monitoring and fast response.

Many systems require very accurate current sensing in the milliamp range up to 1,000 A or more, with several current sensors placed in front of the load to cover the full range. Along with its high bandwidth, the CT45x offers 300 ns response times and high signal-to-noise ratio (SNR), so that a single chip can sense small to large current levels (500 mA up to 1,800 A) with 0.7% accuracy over voltage and temperature.

Crocus said the current sensor ICs translate magnetic fields into a linear analog output voltage. According to the company, the CT45x is housed in eight-lead SOIC or thin eight-lead TSSOP packages.

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For any electronic control system, current sensing is one of the most important forms of performance feedback. Whether the current measurements are used for real-time protection (against short circuits and other surges of current), control loops (e.g., peak-current mode or average-current mode control in power electronics), or power management (e.g., charging and discharging high-voltage battery packs), understanding the ins and outs of the current traveling to loads is vital.

A wide range of current-sensing technologies exist, each one with a long list of pros and cons that must be considered in the context of the overall system and the environmental conditions it is operating in.

But the most common method for measuring current is to put a shunt resistor—also called a current-sense resistor—in the path of the load. Depending on the resistance value, the device outputs a voltage signal that’s proportional to the current traveling through it. Using Ohm's Law, where the relationship of voltage equals current times the resistance (V = I × R), and assuming a stable resistance, the voltage signal can be used—once it’s sufficiently gained and conditioned—to interpret the current.

Shunt-based current sensors are so widespread thanks to their ease-of-use and ability to accurately measure AC and DC currents from milliamps to several hundred amps. While they come with a wide range of form factors and resistance values, shunts can struggle to handle large amounts of power and aren’t galvanically isolated. Thus, they’re not the best fit for every situation. But current transformers and other passive components can fill in for them in many cases.

As power levels continue to rise in everything from electric vehicles (EVs) to solar and other renewable-energy systems to new power-hungry AI processors inside vast data centers, semiconductor companies think they can do better. Allegro Microsystems, ROHM Semiconductor, Texas Instruments, and many others are rolling out current-sensor ICs that they say bring more to the table than traditional passives. In this product roundup, we will review some of the latest offerings to hit the market.

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