Datasheet ACS724 (Allegro) - 29

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Automotive-Grade, Galvanically Isolated Current Sensor IC ACS724 with Common-Mode Field Rejection in a Small-Footprint SOIC8 Package DEFINITIONS OF ACCURACY CHARACTERISTICS Sensitivity (Sens).
The change in sensor IC output in response to Accuracy Across a 1 A change through the primary conductor. The sensitivity is the Temperature Increasing product of the magnetic circuit sensitivity (G / A) (1 G = 0.1 mT) VIOUT (V) and the linear IC amplifier gain (mV/G). The linear IC ampli- Accuracy at 25°C Only fier gain is programmed at the factory to optimize the sensitivity (mV/A) for the full-scale current of the device. Accuracy Across Ideal VIOUT Temperature
Nonlinearity (ELIN).
The nonlinearity is a measure of how linear the output of the sensor IC is over the full current measurement Accuracy at range. The nonlinearity is calculated as: 25°C Only V (I ) – V I +I E = 1– IOUT PR(max) IOUT(Q) • 100(%) PR(min) V P (A) IOUT(Q) LIN 2 • V (I /2) – V IOUT PR(max) IOUT(Q) –IP (A) where VIOUT(IPR(max)) is the output of the sensor IC with the maximum measurement current flowing through it and V Full Scale I IOUT(IPR(max)/2) is the output of the sensor IC with half of the P IPR(max) maximum measurement current flowing through it. 0 A
Zero-Current Output Voltage (VIOUT(Q)).
The output of the sensor when the primary current is zero. For a unipolar supply voltage, it Accuracy at nominally remains at 0.5 × VCC for a bidirectional 25°C Only device and 0.1 × V Decreasing CC for a unidirectional device. For example, Accuracy Across VIOUT (V) in the case of a bidirectional output device, V Temperature CC = 5 V translates into VIOUT(Q) = 2.5 V. Variation in VIOUT(Q) can be attributed to
Figure 4: Output Voltage versus Sensed Current
the resolution of the Allegro linear IC quiescent voltage trim and thermal drift. +ETOT
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 (I Across Temperature P), relative to the actual current. This is equivalent to the difference 25°C Only 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: –IP +IP V (I ) – V (I ) IOUT_ideal P IOUT P E (I ) TOT P = • 100 (%) Sens (I ) • I ideal P P 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 Figure –ETOT 4 and Figure 5. Figure 4 shows a distribution of output voltages versus IP at 25°C and across temperature. Figure 5 shows the cor- responding E
Figure 5: Total Output Error versus Sensed Current
TOT versus IP . 29 Allegro MicroSystems 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com