Currentier

Technical Description

For the reasons outlined in that article, Asahi Kasei Microdevices (AKM) developed the unique coreless current sensor IC, titled “Currentier”. Currentier is the outcome of long experience and unique technology AKM has with compound semiconductor magnetic sensors (Hall elements), package design, and analog circuit design. 

Currentier is used in industrial and residential equipment around the world and contributes to meeting the following requirements:

Benefit

  • Reducing system size (i.e. equipment size)
  • Reducing design man-hours
  • Creating a safer system
  • Improving system efficiency and providing more precise control

Creating a Safer System

In part 3, it will be explained here how Currentier can contribute to creating a safer system.

Need for Isolation

Many control devices, such as general-purpose inverters for controlling motors, AC servo motor drives for precise position control, and controllers for robots to automate operations, mainly operate at 200V or 400V systems. Therefore, it is necessary to firmly isolate between a high voltage primary side and a low voltage secondary side where the controller is placed.

Standards of Isolation

There are standards established by certification bodies such as UL and IEC as criteria for isolation. For example, industrial equipment in North America, systems must achieve isolation that complies with UL61800-5-1. As an index to cope with that, it is necessary to keep creepage/clearance distance of isolation elements such as current sensors and photocouplers above a certain value. For instance, in order to support a 400V system under certain conditions, it is necessary to maintain a creepage/clearance of 8mm or more.

Issues of Isolation

  • The current sensor that can secure creepage/clearances of 8mm or more has only existed in cored current sensors and current transducers, which increases size and cost.
    (Refer to Part 1, “Reducing system size” for details)
  • When using a photocoupler, the number of peripheral parts may increase, which increases the size of substrates and cost.
    (Refer to Part 1, “Reducing system size” for details)
  • When using a photocoupler, heat dissipation due to heat generation of the shunt resistor is increased and thus design man-hours are increased.
    (Refer to Part 2, “Reducing design man-hours” for details)

Creepage/Clearance Distance of 8mm or more

Currentier is the first-class coreless current sensor in the world to achieve creepage and clearances distance of 8mm or more (Figure 1). It is used in industrial equipment worldwide because it can solve all the above-mentioned problems of size, cost, and design man-hours while achieving high insolation.

Figure 1. Isolation standard of Currentier

Needs for Overcurrent Detection

In addition to isolation, overcurrent detection is important for realizing a safe system. Insulated Gate Bipolar Transistor (IGBT) for inverter control are currently being developed from the 6th generation to the 7th and 8th generations, and higher efficiency is progressing. Generally, a trade-off with this efficiency is the so-called “short-circuit tolerance.” Therefore, in order to achieve a high efficiency in a system, it is necessary to shut down the system firmly in a shorter time when an overcurrent flows.

Fast Response Time

Currentier applies AKM's ultra-high sensitivity compound Hall element technology to achieve a response time: 1usec (typ.) 

(Figure 2. Measurement data at N=1 is 0.6usec)

Figure 2. Currentier CZ37xx response time

Circuit Design

The CZ3Axx series is built in dual overcurrent detection with adjustable thresholds. It can achieve a safe system while reducing the number of peripheral components. 
(Figure 3).

Figure 3. Currentier CZ3Axx block diagram

'Currentier' series are open-type current sensor ICs which have the world's smallest package, high accuracy, high S/N ratio, and the world's fastest response time.
With these advantages, we will offer the best current sensing solution to wide-ranging applications, such as inverter control, overcurrent detection, and electrical power detection.

* Currentier is a trademark of Asahi Kasei Microdevices Corporation.