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ACS717

High Isolation, Linear Current Sensor IC with 850 µΩ Current Conductor

Allegro MicroSystems 

ACS717

High Isolation Linear Current Sensor IC with

850 µΩ Current Conductor

DEFINITIONS OF ACCURACY CHARACTERISTICS

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

a 1 A 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:

{ [ ELIN =

1–

VIOUT (IPR(max)) – VIOUT(Q)

2 × VIOUT (IPR(max)/2) – VIOUT(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 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 = 3.3 V translates

into VIOUT(Q) = 1.65 V. Variation in VIOUT(Q) can be attributed to

the resolution of the Allegro linear IC quiescent voltage trim and

thermal drift.

Increasing

VIOUT (V)

Accuracy Across

Temperature

Accuracy at

25°C Only

Accuracy Across

Temperature

Ideal VIOUT

Accuracy at

25°C Only

IPR(min)

–IP (A)

VIOUT(Q)

+IP (A)

Full Scale IP

IPR(max)

0A

Accuracy at

25°C Only

Accuracy Across

Temperature

Decreasing

VIOUT (V)

Figure 1: Output Voltage versus Sensed Current

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.

+ETOT

Total Output Error (ETOT). The 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:

Across Temperature

25°C Only

ETOT(IP) =

VIOUT_ideal(IP) – VIOUT(IP)

Sensideal(IP) × IP

×

100

(%)

–IP

+IP

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 .

–ETOT

Figure 2: Total Output Error versus Sensed Current

Allegro MicroSystems, LLC

9

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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