High Accuracy, Hall-effect Based Current Sensor

IC in High Isolation SOIC16 Package

ACS723KMA

13

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

APPLICATION INFORMATION

Impact of External Magnetic Fields

The ACS723 works by sensing the magnetic field created by the

current flowing through the package. However, the sensor cannot

differentiate between fields created by the current flow and exter-

nal magnetic fields. This means that external magnetic fields can

cause errors in the output of the sensor. Magnetic fields which are

perpendicular to the surface of the package affect the output of

the sensor, as it only senses fields in that one plane. The error in

Amperes can be quantified as:

Error(B) =

B

C

F

where B is the strength of the external field perpendicular to the

G/A. Then, multiplying by the sensitivity of the part (Sens) gives

the error in mV.

For example, an external field of 1 Gauss will result in around

0.22 A of error. If the ACS723KMATR-10AB, which has a nomi-

nal sensitivity of 200 mV/A, is being used, that equates to 44 mV

of error on the output of the sensor.

Table 1: External Magnetic Field (Gauss) Impact

External Field

(Gauss)

Error (A)

Error (mV)

10AB

20AB

40AB

0.5

0.11

22

11

6

1

0.22

44

22

11

2

0.44

88

44

22

Estimating Total Error vs. Sensed Current

The Performance Characteristics tables give distribution (±3

wants to know what error to expect at a particular current. This

can be estimated by using the distribution data for the compo-

nents of Total Error, Sensitivity Error and Offset Voltage. The

E(I) =

TOTP

100 × V

OE

Sens × I

P

E+

SENS

2

()

2

terms. If there is an average sensitivity error or average offset

voltage, then the average Total Error is estimated as:

Sens × I

P

E(I) = E+

TOTP

SENS

AVGAVG

100 × V

OEAVG

Using these equations and the 3 sigma distributions for Sensitiv-

ity Error and Offset Voltage, the Total Error vs. sensed current

goes towards zero current, the error in percent goes towards infin-

ity due to division by zero (refer to Figure 3).

15.00

10.00

5.00

0.00

-5.00

-10.00

-15.00

0

510152025

30

35

40

-40C+3sig

-40C-3sig

25C+3sig

25C-3sig

125C+3sig

125C-3sig

Current (A)

Figure 3: Predicted Total Error as a Function of Sensed

Current for the ACS723KMATR-40AB