ACS724 datasheet(21/25 Pages) ALLEGRO

21 / 25 page

Automotive-Grade, Galvanically Isolated Current Sensor IC

With Common-Mode Field Rejection in a Small-Footprint SOIC8 Package

ACS724

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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

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

product of the magnetic circuit sensitivity (G/A) (1 G = 0.1 mT)

and the linear IC amplifier gain (mV/G). The linear IC ampli-

fier gain is programmed at the factory to optimize the sensitivity

(mV/A) for the full-scale current of the device.

Nonlinearity (ELIN). The nonlinearity is a measure of how linear

the output of the sensor IC is over the full current measurement

range. The nonlinearity is calculated as:

LIN

1–

V(I

)–V

IOUT

PR(max)

IOUT(Q)

2• V(I

/2) –V

IOUT

PR(max)

IOUT(Q)

• 100(%)

where VIOUT(IPR(max)) is the output of the sensor IC with the

maximum measurement current flowing through it and

VIOUT(IPR(max)/2) is the output of the sensor IC with half of the

maximum measurement current flowing through it.

Zero-Current Output Voltage (VIOUT(Q)). The output of the

sensor when the primary current is zero. For a unipolar supply

voltage, it nominally remains at 0.5 × VCC for a bidirectional

device and 0.1 × VCC for a unidirectional device. For example,

in the case of a bidirectional output device, VCC = 5 V translates

into VIOUT(Q) = 2.5 V. Variation in VIOUT(Q) can be attributed to

the resolution of the Allegro linear IC quiescent voltage trim and

thermal drift.

Offset Voltage (VOE). The deviation of the device output from

its ideal quiescent value of 0.5 × VCC (bidirectional) or 0.1 × VCC

(unidirectional) due to nonmagnetic causes. To convert this volt-

age to amperes, divide by the device sensitivity, Sens.

Total Output Error (ETOT). The difference between the cur-

rent measurement from the sensor IC and the actual current (IP),

relative to the actual current. This is equivalent to the difference

between the ideal output voltage and the actual output voltage,

divided by the ideal sensitivity, relative to the current flowing

through the primary conduction path:

E(I)

TOTP

V(I )–V

(I )

IOUT_idealP

IOUT

Sens

(I )• I

idealP

• 100 (%)

The Total Output Error incorporates all sources of error and is a

function of IP. At relatively high currents, ETOT will be mostly

due to sensitivity error, and at relatively low currents, ETOT will

be mostly due to Offset Voltage (VOE). In fact, at IP = 0, ETOT

approaches infinity due to the offset. This is illustrated in Figures

1 and 2. Figure 1 shows a distribution of output voltages versus IP

at 25°C and across temperature. Figure 2 shows the correspond-

ing ETOT versus IP.

DEFINITIONS OF ACCURACY CHARACTERISTICS

Figure 1: Output Voltage versus Sensed Current

Figure 2: Total Output Error versus Sensed Current

0 A

Decreasing

VIOUT (V)

Accuracy Across

Temperature

Accuracy Across

Temperature

Accuracy Across

Temperature

Accuracy at

25°C Only

Accuracy at

25°C Only

Accuracy at

25°C Only

Increasing

VIOUT (V)

Ideal VIOUT

IPR(min)

IPR(max)

+IP (A)

–IP (A)

VIOUT(Q)

Full Scale IP

+IP

–IP

+ETOT

–ETOT

Across Temperature

25°C Only

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