Allegro Microsystems discusses the advances of a new integrated linear current sensor IC that can be used for more effective AC or DC current sensing in audio and communications systems
Replacing sense resistor op-amp current sensing configurations is no easy task and requires a certain sophistication of technology that has the capability to handle this, such as linear current sensor IC technology.
In response, there are companies developing chip technology that is ideally suited, For instance there are new current sensor linear ICs available from Allegro Microsystems in the form of the ACS711. These devices are designed for low-side or <100V sensing applications and can sense up to 30A continuous current.
Key performance characteristics
To enable performance capabilities for demanding applications such as AC or DC current sensing in <100V audio, communications systems, and white goods applications, the sensors are enhanced with the company’s latest flip-chip technology.
This enables better magnetic coupling and assists with the small design of the sensing solution. Current flows in and out of the package through the primary conductor loop. This current generates a magnetic signal that is sensed by the Hall transducer, and is converted to a voltage. The voltage is dependent on the direction of the current flow and so bi-directional current flow of both AC and DC currents is possible using this Hall Effect current sensor.
The transducer is placed in the area of highest flux density to optimise the magnetic coupling. The flip-chip technology also allows the active area of the transducer to be in closer proximity to the conductor, which improves the signal coupling because the active area of the Hall transducer is on the surface of the silicon closest to the primary conductor.
The QFN configuration conductor resistance is only 0.6m2, which is an order of magnitude smaller than most sense resistors employed in low-side sensing configurations.
This saves power consumption in customer applications and allows for a higher efficiency and more eco-friendly current sensing solution. A small footprint also saves PCB area, thereby reducing overall system cost.
To optimise the advantage of the small primary current path resistance and maximise the amount of continuous current that can flow through the package, conducting heat away from the device must be considered.
The graph (Figure 2) shows that at an ambient temperature of 85°C the sensor package can withstand 45A continuous current before reaching the maximum recommended thermal junction (die) temperature of 165°C.
With proper PCB design, the device can be safely used in 30A continuous current applications up to 85°C ambient temperature, with greater than 40°C of safety margin before reaching a die temperature of 165°C.
Sense resistor op-amp solutions suffer accuracy error as the sense resistor changes with temperature. Since the magnetic field generated by current flowing in a conductor is not temperature dependent, Hall sensors are not subject to this error term.
In addition, the fully integrated architecture of the sensor allows for the major error terms, both gain and offset, to be programmed at end of line production to produce a more accurate Hall-effect current sensing solution that is easy for designers to employ in the application.
The sensor IC also integrates a factory programmed fast response digital fault output that has a 1.3µs response time. This fast fault can be used to prevent the destruction of IGBT’s or other switching devices during short circuit or over-current conditions, or as a redundant fault feature in motor control applications.
The company’s flip-chip packaging for linear Hall ICs creates a micro sized 3mm by 3mm fully integrated current sensor device, with only a 0.6m2 internal resistance producing a package that can really take the heat.
With proper PCB design the device can be used for applications with over 30A continuous current while reducing power consumption by an order of magnitude over existing sense resistor op-amp solutions. Factory programming provides for high accuracy in this IC with an integrated fast response fault output.
These techniques all work to deliver a small current sensing footprint for application without compromising accuracy.
Allegro Microsystems
