Accurate, high-isolation, differential current sensor ICs

April 07, 2016 // By Graham Prophet
Allegro MicroSystems Europe has added current sensor ICs that it positions as economical and precise solutions for AC or DC current sensing, in industrial, commercial, and communication systems that require very high voltage isolation.

Both the ACS724KMA (5V) and the ACS725KMA (3.3V) are available in a very small package for space-constrained applications. They are packaged in a high-isolation SOIC16 wide body surface mount package that provides reinforced isolation. The differential sensing technology provides immunity to interfering common mode magnetic fields from adjacent current traces or motors. Typical applications include motor control, load detection and management, switched-mode power supplies, and overcurrent fault protection.

Both devices consist of a precise, low-offset, linear Hall sensor circuit with a copper conduction path located near the surface of the die. Applied current flowing through this copper conduction path generates a magnetic field which is sensed by the integrated Hall IC and converted into a proportional voltage. The current is sensed differentially in order to reject common-mode fields, improving accuracy in magnetically noisy environments.

The inherent device accuracy is optimised through the close proximity of the magnetic field to the Hall transducer. A precise, proportional voltage is provided by the low-offset, chopper-stabilised BiCMOS Hall IC, which includes Allegro’s digital temperature compensation, resulting in extremely accurate performance over temperature.

The output of the device has a positive slope when an increasing current flows through the primary copper conduction path, which is the path used for current sensing. The internal resistance of this conductive path is 0.85 mΩ typical, for low power loss.

The terminals of the conductive path are electrically isolated from the sensor leads. This allows the current sensor IC to be used in high-side current sense applications without the use of high-side differential amplifiers or other costly isolation techniques.

The ACS724KMA and ACS725KMA are provided in a low-profile surface-mount SOIC16 package. These devices are not intended for use in automotive applications.

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