Fully Integrated, Hall Effect-Based Linear Current Sensor with

2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor

ACS712

8

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

Sensitivity (Sens). The change in sensor output in response to a

1A change through the primary conductor. The sensitivity is the

product of the magnetic circuit sensitivity (G/A) and the linear

IC amplifier gain (mV/G). The linear IC amplifier gain is pro-

grammed at the factory to optimize the sensitivity (mV/A) for the

full-scale current of the device.

(mV/G) and the noise floor for the Allegro Hall effect linear IC

(≈1 G). The noise floor is derived from the thermal and shot

noise observed in Hall elements. Dividing the noise (mV) by the

sensitivity (mV/A) provides the smallest current that the device is

able to resolve.

the sensor varies in direct proportion to the primary current

through its full-scale amplitude. Nonlinearity in the output can be

attributed to the saturation of the flux concentrator approaching

the full-scale current. The following equation is used to derive the

linearity:

output from the sensor varies in proportion to either a positive

or negative full-scale primary current. The following formula is

used to derive symmetry:

when the primary current is zero. For a unipolar supply voltage,

resolution of the Allegro linear IC quiescent voltage trim and

thermal drift.

causes. To convert this voltage to amperes, divide by the device

sensitivity, Sens.

tion of the actual output from its ideal value. This is also known

as the total ouput error. The accuracy is illustrated graphically in

the output voltage versus current chart at right.

Accuracy is divided into four areas:

•

0 A at 25°C. Accuracy of sensing zero current flow at 25°C,

without the effects of temperature.

•

0 A over Δ temperature. Accuracy of sensing zero current

flow including temperature effects.

•

Full-scale current at 25°C. Accuracy of sensing the full-scale

current at 25°C, without the effects of temperature.

•

Full-scale current over Δ temperature. Accuracy of sensing full-

scale current flow including temperature effects.

Ratiometry. The ratiometric feature means that its 0 A output,

used to derive the ratiometric change in 0 A output voltage,

Δ

Definitions of Accuracy Characteristics

100 1–

[{

[ {

∆ gain × % sat (

)

100





100





100

‰



Output Voltage versus Sensed Current

Accuracy at 0 A and at Full-Scale Current

Accuracy

Accuracy

Accuracy

25°C Only

Accuracy

25°C Only

Accuracy

25°C Only

Accuracy

0 A

v r

O e Temp erature

Average

v r

O e Temp erature

v r

O e Temp erature

Full Scale