Common mode field rejection in coreless hall-effect current sensor ICs

Allegro current sensor ICs use the Hall-effect to measure the magnetic field produced by an integrated, current carrying loop, translating the magnetic field to a voltage which is proportional to the current flow. This technology has many advantages, including galvanic isolation, low power loss, and high accuracy over temperature. This technology also has near zero magnetic hysteresis, as there is no core used for concentrating the field.
However, the disadvantage of not using a core is that the sensor IC is susceptible to stray magnetic fields. With a core, stray magnetic fields are shunted around the sensor IC, as the core provides a low reluctance path around the sensor IC. Without the core, stray fields from high current carrying traces or solenoids, for example, will be seen by the Hall plate and may result in error in the current measurement. Proper board and system design can avoid these sources of error in the current measurement; however, optimized trace layout can undesirably constrain the PCB and system design. The solution to this issue is integrated differential current sensing.