Optimizing System Performance with Precision Current Sensing

June 11, 2019 Khagendra Thapa, ACEINNA

Because of its vital nature, power is ubiquitous in electronics, as nothing happens until energy moves through a circuit. Power density, energy efficiency, and reliable operation are all critical factors to consider in modern electronics. These issues, as well as the important related aspects like the solution footprint and the system’s thermal management, drive developers to improve power systems performance in many areas.

A lot of attention is being paid to improving core technologies, next generation power topologies, advanced software-defined electronics, and developing advanced materials like wide-bandgap semiconductors. From using Artificial Intelligence to power conversions and management, to drive power switches in various application more accurately designers are creating power systems that are pushing the boundaries of what is theoretically possible.  

No Precision Without Feedback

One of the beautiful things about engineering is that there are multiple solutions to any given problem, and sometimes it may not be the newest shiniest technology. In the area of power system performance, an often overlooked means to improve operation is better performance monitoring. There is no precision without feedback, and the more you know about the way the circuit is performing, the more you can do to optimize it.

One of the biggest advantages to improved system oversight is that it leverages everything in the system, as it is technology agnostic. You can have the best semiconductors, in the latest circuit designs, driven by the most advanced software, and improved performance measurement will give you even better performance. There is no downside to knowing more about how any given circuit performs. The more accurate the information you have, the more precise your system can be.

In high-performance computing systems, power is a critical part of the infrastructure. How you monitor power can optimize performance, manage processor workloads, and in general make the system more cost-effective. Measuring the current flow into a system tells you if it's running at an optimal level, and if you can load more computations, or workload, onto the processor. In addition, precise current sensing increases profitability as you can more accurately bill clients based on the actual computational power used.

Current Sensing

Current sensing is an important way to get precise performance feedback, providing insights into how the system is operating, by measuring the power flow within the system. Enabling dynamic control of switching frequencies to minimize losses, accurate and fast current measurement is also key to reducing loss in zero-current and zero-voltage switching systems.

Current sensors are used in a wide range of control, protection, and measurement circuits to measure the power flow within the system.

AMR Technology
Offering high accuracy and bandwidth in a small package, Anisotropic Magnetoresistive (AMR) isolated current sensors, like the ones from ACIENNA, are drop-in devices. Made from an NiFe thin film that exhibits a very high-sensitivity and high-bandwidth response to magnetic fields, an AMR-based current sensor outperforms sense resistors, Hall-effect devices, and current transformers.

Compared to sense resistors, Hall-effect devices, and current transformers, AMR-based current sensors exhibit a very high sensitivity and high-bandwidth response to magnetic fields.

Compared to legacy methods, an AMR based sensor’s construction lends itself well in applications where isolation is needed. A shunt resistor, for example, can measure the voltage dropped across it, but is inherently not isolated. Adding isolation requires additional components, increasing cost, solution size and associated development problems. Isolation is important in electronic systems, especially in applications requiring a high level of accuracy and precision, as the amount of noise and interference in a circuit directly impacts performance.

Using a current transformer can result in a bulky solution footprint, and a transformer’s weight can be an issue in a compact design. In addition, transformers only work in AC circuits, and have a saturation effect, where the linearity of the transformer is disturbed, leading to clipping and increased temperatures in the core. You can put a Hall-effect sensor in and use it to measure the current through the wire, but it is susceptible to external magnetic fields and can be affected by temperature and stress, which can change the output. The sensor type used in a power design impacts the cost, size, and effectiveness of its final configuration.

A compact, single-chip solution, ACEINNA’s AMR technology uses an insulating substrate, with 4.8KV isolation, and as compared to a shunt resistor, does not require additional components other than a decoupling capacitor. Compared to a transformer, beyond the size advantages, AMR tech can respond to both DC and AC bi-directional current. Compared to Hall-effect-based solutions, AMR tech offers a bandwidth of 1.5 megahertz, lower offset, and noise, leading to better accuracy and a lower phase shift.

How it Works
The ACIENNA sensor has four pins that take the current in, and on the same side another four pins provide the output. As the current flows through the lead frame, it flows through a U-shaped bend. As the current flows through the bend in the lead frame, it generates a field to be measured. When the current reverses, it has a reverse field. Two separate AMR current sensors in the device measure the field from both current directions, which also cancels out any external magnetic fields and offsets.

 To ensure high accuracy, the two (GREEN) AMR current sensors measure the field from both current directions, essentially canceling out external magnetic fields

Enabling the ability to ignore external fields perpendicular to the current flow, the dual-sensor configuration of an AMR sensor makes it only sensitive to horizontal fields in the silicon. In the case of a Hall-effect sensor, they also sense fields perpendicular to the silicon. An AMR-based sensor’s resistance to stray magnetic fields gives developers much more flexibility in system design and component placement.

In addition to high accuracy and bandwidth, the dual-sensor construction of an ACIENNA AMR sensor, its materials, and its high level of integration, also provides fast output step response, which is the ability of the sensor to rapidly react to changes in the magnetic fields. This combination of speed and precision successfully reduces phase differences in the signal and errors that can be created by slow and inaccurate measurements.

AMR Sensor Features
Power is also a critical part of our data infrastructure, especially in applications like power supplies in servers and telecom. In these and any other system where you have a front-end AC-DC PFC converter feeding DC-DC bus and Point-of-Load converters, an AMR sensor is the best choice for system performance feedback. There can be no accuracy without feedback and knowing exactly how a systems is performing enables you to properly manage it.

ACIENNA’s recently-released MCx1101 family of ±5A, ±20A, and ±50A current sensors for industrial and power supply applications, for example, are integrated bi-directional current sensors with (at ±20A) a typical accuracy of ±0.6 perent, and an offset of ±60mA, or ±0.3 percent of FSR (max) over temperature. This level of accuracy enables precise adjustments in any given system to maximize performance wherever possible.

An AMR-based integrated single-chip solution also has a reduced offset voltage, the difference between the actual output and the specified value, which affects the accuracy of the measurement. The sensor’s AMR technology and high level of integration results in less noise, which impacts the accuracy of any device. A high level of accuracy can better optimize how a given processor is used, especially in AI- and Cloud-based applications, providing power tracking for performance monitoring.

Application Advantages
Awareness of the energy each server is using in a system can help determine whether there's still room for more number-crunching in the system, or if it's already at limit. Knowing how your power is consumed also lets you charge your customer based on how much processor time or processing power is being used.

Many other applications can benefit from AMR current sensing, especially those using motor drives and inverters. Operationally similar, inverters and motor drives differ in the nature of the load served, so they can also similarly benefit from better current monitoring. Uninterruptible power supplies (UPS) can also benefit, in every subsystem from the front AC-DC converter to the final stage DC-AC inverter, as well as the battery management circuit and where the UPS connects to the grid.

An AMR current sensor on the output side enables the inverter or UPS systems to synthesize the sine waves to connect to the grid. When it comes to power factor correction (PFC), in a totem-pole PFC topology, an AMR sensor can measure the current, for both better control and protection.

In battery management, it's about charge and discharge current management. In addition, home appliances, especially those with motors, like refrigerators and dishwashers, can also benefit.

Proper Power Management

In applications like power, motor control, inverters, UPS, and electric vehicles, AMR sensors are often the best choice for a monitoring solution to improve performance. These dynamic applications require fast, rugged, and accurate power measurement, and an AMR sensor’s construction and materials provide an inherently high sensitivity, fast response, and wide bandwidth. These attributes, isolation, accuracy, and performance makes an AMR-based current sensing solution the best choice to serve advanced power management in next-generation systems.

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AUTHOR BIO

Khagendra Thapa, VP of Business Development of ACEINNA’s Current Sensing business, has over 21 years of business management and leadership experience in the electronics equipment and semiconductor industry.

Mr. Thapa holds a Bachelor’s degree in Electronics and Communication, a Master degree in Power Electronics from University of Birmingham in the U.K. and MBA from Manchester Business School in the U.K. He started his career in graduate management training program in the U.K. 

With a strong engineering background, he excelled as a Senior Design Engineer and Principle System Engineer, then moved on to take various senior roles as a WW Strategic Marketing Manager, Business Unit Director and Senior Director of Business Development in the past both in the U.K. and USA.

ABOUT ACEINNA

ACEINNA Inc., headquartered in Andover, Massachusetts, provides leading edge MEMS-based sensing solutions that help our customers improve the reliability, cost, features, and performance of their end products and equipment. In 2017, ACEINNA was spun off from MEMSIC, which is now a part of a public company. ACEINNA has been developing MR based sensor and magnetic thin film manufacturing for 15 years. ACEINNA provides a proven technology platform with over 300M MR based electronic compass units that have been integrated into mobile devices, automotive and industrial applications. The company has manufacturing facilities in Wuxi, China, and R&D facilities in San Jose, CA, Andover, MA, and Chicago, IL.

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