Product Insight: Allegro’s ACS712 Hall-Effect Current Sensor IC

8 feb 2018

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Arrow Electronics

Miguel Gudino is an electrical engineer that specializes in electronic passive components and computer organization. He b... Continua a leggere

The ACS712 IC from Allegro is a Hall Effect Sensor that has been popular for the last few years. This is because of its compactness, cost effectiveness, and precise solution for AC or DC current sensing in industrial, commercial, and communication systems, being able to measure current that ranges from 5A, 20A, and 30A.

How does a Hall Effect Sensor Work?

The AC712 uses a precise, low-offset, linear Hall sensor circuit in order to measure the current passing through the IC. It’s called a Hall sensor because it uses the theory of the “Hall Effect”, where an electric current goes through an electrical conductor and a magnetic field is applied perpendicular to the electrical conductor. This then produces a voltage difference across the electrical conductor.

When there is no magnetic field, the current flows in a “straight line” across the electrical conductor. When you apply a magnetic field perpendicular to the electrical conductor, the current does not flow straight any more. It causes the current to “curve”, thus moving positive charges on one end and moving negative charges to the other end, which causes this to have a voltage difference on the electrical conductor. Figure 1 shows an illustration on how the Hall Effect works.

Figure 1: A magnetic field causing current to curve, a Hall Effect (Source: Digilent/James Colvin)

The Allegro ACS712 IC

The ACS712 senses the current by having current flow in and out of the package. The current flow generates a magnetic field around a loop inside the IC that is proportional to the magnitude of the current flowing in the electric conductor. The Hall-Effect sensor senses the magnetic field generated by the current flowing in the conductor, turning the magnetic field into a voltage. The power loss is very low, making the ACS712 highly efficient in sensing current.

With its flip-chip technology, the sensor allows the Hall transducer to be placed right over the portion of the loop where the magnetic field is the strongest. This also allows for the connections between the signal leads of the IC, to the package leads on the other side of the package. While the Hall sensor is close to the current loop, there is an insulating layer of plastic in between the two, providing high-voltage isolation and allowing it to be used in AC tight applications. Figure 2 shows the current going in and out of the package and producing a voltage signal.

Figure 2: Current flowing in and out of the package producing a magnetic field. Magnetic field is then converted into a voltage (Source: Allegro Micro)

Features for the Allegro ACS712 (from Allegro Micro’s site) include:

• Low-noise analog signal path
• Device bandwidth is set via the new FILTER pin
• 5 µs output rise time in response to step input current
• 80 kHz bandwidth
• Total output error 1.5% at TA = 25°C
• Small footprint, low-profile SOIC8 package
• 1.2 mΩ internal conductor resistance
• 2.1 kVRMS minimum isolation voltage from pins 1-4 to pins 5-8
• 5.0 V, single supply operation
• 66 to 185 mV/A output sensitivity
• Output voltage proportional to AC or DC currents
• Factory-trimmed for accuracy
• Extremely stable output offset voltage
• Nearly zero magnetic hysteresis
• Ratiometric output from supply voltage