Melexis Current Sensor for Ultracapacitor CMS

FROM IDEA TO INTEGRATION: Melexis Current Sensor for Ultracapacitor CMS

Dimac Red is much more than a simple distributor. Our engineers support customers in the design-in activity of Melexis products, bringing their ideas together in the product development. From the early stage of the design to prototyping and production, they are on your side!

Applying MLX91208 IMC-Hall in a battery or Supercapacitor Management System

Here’s an example of how we apply MLX91208 IMC-Hall in a Battery (or Supercapacitor) Management system implemented together with the Ultracapacitor Module C-BOX (54V, 166F). (Fig.1)

The CMS controls the charge and discharge of the ultracapacitor battery, with an RMS current of 200A which could reach a peak value of 2000A. The current measurement is galvanically separated from the ultracapacitor thanks to the Hall effect sensor. In this way, it measures the magnetic field produced by the current. Then, the current flows in five layers of superimposed copper inside a PCB (printed circuit board). In the meantime, the sensor, which is mounted on the top layer, measures the total magnetic field.

The magnetic field, (Fig.2) due to the current in the five layers, is parallel to the surface of the PCB and the MLX91208 sensor is particularly suitable for this measurement because it quantifies the magnetic field parallel to its surface. This characteristic is attributable to the Integrated Magneto-Concentrator (IMC-Hall) inserted into the sensor which, unlike conventional planar Hall technology, is sensitive to the flux of the magnetic field parallel to the surface.

More properties

Other embedded properties of this sensor are the 5V voltage and the analog ratiometric output:

  • when the current is 0 A and the magnetic field is 0mT, the output is 2.5V, the middle point between 0 and 5V. When the current and the relative magnetic field are positive, the output varies between 2.5V and 5V. Vice versa when the current is negative, the output varies between 0V and 2.5V.
  • the output voltage is a function of the sensor’s sensitivity and the value of the magnetic field (measured in mT).
  • the standard sensor sensitivity is 250mV/mT.

By using the MELEXIS PTC04 programmer and the related PTC04-DB Hall05 Daughter Board, you can calibrate the sensor. As a result, the sensitivity can be programmed from 100mV/mT to 700mV/mT. (Fig.3)

The calculation of the magnetic field due to a current flowing in a copper layer of width W can be approximated with the following formula:

In any case, this formula is inaccurate. When the width of the copper layer is much greater than the dimensions of the component. By using MELEXIS application software, you can achieve the best sensor programming.
The procedure consists on one hand in fixing a precise flux current value in the copper layers underlying the component. On another hand in programming the desired output voltage in correspondence with this current.

The width of the five layers is 30mm, therefore the fixed current is 100 A.
The sensor can provide 3.75 V with a fixed current of 100 A. In this way, the output voltage is 5V with a maximum current of 200A.

Dimac Red engineers’ work

Figure 4 shows the width of the copper layers under the sensor and the position of the sensor on the top layer. By mastering a wide knowledge and by staying up-to-date on new specific functions and applications, Dimac Red engineers work alongside customers to link their purposes with the products provided by exceptional suppliers such as Melexis, supporting professionals and designers to use High-Reliability electronic devices, programmers, and any type of tools and resources. Our effort toward a Design-In result is essential to make your Idea an Integration!
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Figure 1: C-mode Ultracapacitor module with BMS. MLX91208

Figure 2

Figure 3

Figure 4: MLX91208