Four Reasons for Current Sensing Integrated Current Sensors
Current sensing is critical in a variety of electronic devices, including power supplies, battery management systems, motor drives, and renewable energy networks. Accurate and reliable current sensing is critical to the protection and efficient operation of these devices.
However, current measurement faces challenges as device power density increases, and the goal is always to do more with less, including minimizing circuit board footprint. In this space-constrained and high-power-density environment, integrated current sensors (ICS) play a vital role.
ICS are Hall effect-based current sensors ideally suited for a variety of automotive, industrial or residential applications that integrate a current conductor, sensing element, signal processing chip and some specialized functions such as fault detection and isolation in a single package.
Hall effect sensing is a method to achieve non-contact measurement of current-induced magnetic fields. Hall elements are sensing elements that convert magnetic field changes into changes in their resistance. When a constant current passes through the Hall cell, the voltage output changes proportionally to the magnetic field.
Four main advantages illustrate why integrated current sensors may be a sound investment.
Traditional Hall effect current sensors use a ferrite core around the current conductor and sensing element to concentrate the magnetic field. The core also protects against unwanted external magnetic fields and noise. Differential measurement makes it possible to remove the ferrite core using two sensing elements (Hall cells), both of which receive the magnetic field to be measured - one with a positive factor and the other with a negative factor. The difference between the two magnetic fields eliminates any additional unwanted magnetic fields.
Integrated current sensors use differential measurements to avoid the use of ferrite cores. Removing the core brings several advantages to embedded applications. For example, device cost is reduced, power density on the sensing side is mechanically increased (LEM ICS products are up to 75A in 800V applications), and measurements are not affected by hysteresis (when an external magnetic field is applied to a ferromagnet and the atomic dipoles are aligned with it). , frequency and bandwidth are not limited by the inherent saturation of the core's magnetic components.
Some systems require specific isolation to protect end users, which means the user interface must be physically isolated from the high voltage (HV) network and cannot share the same voltage reference level. ICS integrates isolation functions both inside the device (galvanic isolation) and outside (creepage and clearance distances), which means there is no physical connection between the primary conductor, where high-voltage current flows, and the secondary circuit with an application-specific integrated circuit (ASIC) chip and auxiliary pins. These two sides communicate only through the magnetic field created by the flowing electric current.
The ASICs in ICS are produced using CMOS semiconductor manufacturing processes, allowing specific functionality to be integrated into the component without the need for additional hardware. For example, all analog and digital components required to sense, amplify and process proportional voltage signals are fabricated on a single chip using semiconductor materials, which also ensures low power and power consumption.
Overcurrent detection (OCD) is also an important factor. With the internal OCD, when the current exceeds a threshold, it internally triggers a signal output to a dedicated fault pin. This allows the application's microcontroller to receive alert information with minimal latency. Otherwise, this would have to be done internally based on the current level sent by the sensor, which would take much longer.
Figure 1. OCD enables the microcontroller to react to overcurrent with a minimum delay.Image courtesy of Hakata Electric Power Systems
Compensation and additional integration features
As for stress and temperature compensation, sensitivity drift may occur if the ASIC chip is subjected to mechanical stress from the package (the same thing will happen with a temperature change of -40°C to +125°C). Internal sensors in the ASIC chip compensate for this drift to ensure linear and accurate sensitivity over a wide range of conditions. In discrete-based designs, the temperature of the shunt varies greatly with resistive losses, requiring additional design steps in the microcontroller to accurately compensate for this. In contrast, ICS solutions are plug-and-play.
Figure 2. ICS embeds the primary conductor, two sensing elements, etc. on the chip.Images used courtesy of Bodo's Power Systems
Traditionally, the voltage output is always proportional to the measured current, but there are two possible reference voltages. In ratio mode, Vout is expressed as a percentage of the supply voltage Vcc, which requires a stable supply voltage. In fixed (non-ratio) mode, Vout is compared to an external reference voltage, Vref. The proportional signal is Vout minus Vref, but when the current to be measured is 0A, Vout = Vref - in other words, the reference voltage sets the static output voltage (zero current mode).
LEM has developed two ICS series: HMSR series and GO series. LEM HMSR and GO-SMS ICS feature internal and external OCD for optimal system protection. Depending on the system characteristics, they can also provide proportional and fixed voltage outputs as required. While the LEM HMSR series offers additional immunity through its integrated core, the LEM GO series takes full advantage of differential measurements in a compact surface mount small outline integrated circuit (SOIC)
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