What you’ll learn:

Options for high-voltage current sensing.
Historical challenges with in-package Hall-effect current sensors.
In-package Hall-effect current sensor working principles.

For those systems incorporating high-voltage domains, signal and power isolation can help protect people and critical circuits from high-voltage ac or dc power sources and loads. Adding more electrical functionality makes it increasingly important to shrink these systems to make them easier to scale while also reducing bill of materials, simplifying design, and maintaining high performance.

In high-voltage systems, current sensing handles overcurrent protection, monitoring and diagnostics, and closed-loop control. Furthermore, high-voltage systems often require high accuracy for monitoring and controlling loads to maximize efficiency. Power-factor-correction (PFC) circuits, for example, require the accurate sensing of ac currents to improve system efficiency and monitor energy consumption. High-voltage motors require precise in-line motor-current sensing for accurate torque control of the motor.

With so many requirements and variables, it can be difficult to know which current-sensing approach is best for your design. This article explores the tradeoffs and considerations between three different current sensors.

Options for High-Voltage Current Sensing

You have three main options for measuring current in high-voltage applications: isolated shunt-based current sensors, closed-loop Hall-effect current sensors, or in-package Hall-effect current sensors.

Isolated shunt-based and closed-loop Hall-effect current sensors provide the highest levels of accuracy and isolation (Table 1). However, they’re more expensive and larger than in-package Hall-effect current sensors and have more complex designs since they require external components.

Historical Challenges with In-Package Hall-Effect Current Sensors

If size and cost are equally critical to your design, in-package Hall-effect current sensors may be your best option. They can enable high-voltage isolated measurements in a simple, small form factor that requires no external components. However, they’ve historically drifted over time and temperature, which limits their accuracy.

Designers have attempted to reduce this drift and nonlinearity through linear correction efforts, but even these approaches can’t achieve sensitivity below 2%-3% across temperature. Moreover, they only calibrate to temperature at time zero, or a single point in time. To further improve accuracy and lower the sensitivity specification, you could try conducting system-level multipoint calibration to account for temperature drifts. This effort is limited by the testing capabilities, though, plus it adds more cost and takes longer to get a product to market.

The TMCS1100 family of zero-drift in-package Hall-effect current sensors developed by Texas Instruments eliminates this tradeoff.

In-Package Hall-Effect Current-Sensor Working Principles

These zero-drift in-package Hall-effect current sensors enable current flow through the leadframe, which is electrically isolated from the die. The leadframe loop then generates a magnetic field proportional to the current, and a precision Hall-effect sensor converts that magnetic field to a voltage signal

The TMCS1100 provides <1% total error current measurement, and its zero-drift precision signal-chain-architecture improves drift over temperature and eliminates the need for multipoint calibration. In addition, the accuracy helps boost efficiency in systems for better control, while minimizing complexity for any application that needs high-precision isolated current measurements.

Both the TMCS1100 and TMCS1101 provide sufficient lifetime isolation margin and 600 V of working voltage in an 8-pin small-outline IC (SOIC) package with higher lifetime margins than what’s required by industry standard

Hall-effect sensors are commonly used in automotive and industrial systems for applications including proximity detection, linear displacement measurement and rotary encoding. Currently, the high system performance requirements of modern applications have led to IC manufacturers increasing sensitivity accuracy, integrating more functionality, expanding available sensing directionalities and lowering power consumption in their devices – helping extend the use of Hall-effect sensors for decades to come.

This article introduces Allegro’s ACS71x current sensor integrated circuits (ICs) without concentrator that can control and minimize external magnetic field interference. These devices can boost performance of small-current differentiation with an easy layout steps.

The ACS71x families of Hall effect-based electrical current sensor ICs measure current by sensing the magnetic field it generates as it passes adjacent to the Hall element (see figure 1). They measure this field directly, without the use of a magnetic concentrator, which is a common feature in other magnetic devices (for example, in the Allegro® MicroSystems CA and CB packages, used for the ACS75x families of current sensor ICs).

The lack of a concentrator has the advantage of nearly eliminating magnetic hysteresis as a source of error in the IC. However, this also leaves the ACS71x devices less shielded from external magnetic fields that could distort the current measurement. In applications where large magnetic fields may be present, care must be taken in the alignment and spacing of the Hall element relative to those fields. Shielding the device may also be desirable in some circumstances.

High-current conductors in the vicinity of the device should be, if possible, oriented perpendicular to the plane on the board on which the device package is mounted

Managing External Magnetic Field Interference When Using ACS71x Current Sensor ICs
http://www.allegromicro.com/en/Design-Center/Technical-Documents/Hall-Effect-Sensor-IC-Publications/Managing-External-Magnetic-Field-Interference-ACS71x-Current-Sensor-ICs.aspx?sc_camp=64EB2DD6B3FE4C088C07DB87D5D9B6EF

Please note than in them there is quite small insulation distance between the measured side and output side, so I would not use many of them them to measure mains voltages.