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High Bandwidth, Fast Fault Response Current Sensor IC In Thermally Enhanced Package ACS709 14 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Sensitivity (Sens). The change in device 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. Noise (VNOISE). The product of the linear IC amplifier gain (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. Linearity (ELIN). The degree to which the voltage output from the device 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: where VIOUT_full-scale amperes = the output voltage (V) when the sensed current approximates full-scale ±IP . Symmetry (ESYM). The degree to which the absolute voltage output from the device varies in proportion to either a positive or negative full-scale primary current. The following formula is used to derive symmetry: Quiescent output voltage (VIOUT(Q)). The output of the device when the primary current is zero. For a unipolar supply voltage, it nominally remains at 0.5×VCC. 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. Electrical offset voltage (VOE). The deviation of the device out- put from its ideal quiescent voltage due to nonmagnetic causes. To convert this voltage to amperes, divide by the device sensitivity, Sens. Accuracy (ETOT). The accuracy represents the maximum devia- 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. Note that error is directly measured during final test at Allegro. 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, VIOUT(Q), (nominally equal to VCC/2) and sensitivity, Sens, are proportional to its supply voltage, VCC.The following formula is used to derive the ratiometric change in 0 A output voltage, VIOUT(Q)RAT (%). The ratiometric change in sensitivity, SensRAT (%), is defined as: Definitions of Accuracy Characteristics 100 1– [{ [ { VIOUT_full-scale amperes – VIOUT(Q) 2 (VIOUT_1/2 full-scale amperes – VIOUT(Q)) 100 VIOUT_+ full-scale amperes – VIOUT(Q) VIOUT(Q) – VIOUT_–full-scale amperes 100 VIOUT(Q)VCC / VIOUT(Q)5V VCC / 5 V 100 SensVCC / Sens5V VCC / 5 V Output Voltage versus Sensed Current Accuracy at 0 A and at Full-Scale Current Increasing V IOUT(V) +I P (A) Accuracy Accuracy Accuracy 25°C Only Accuracy 25°C Only Accuracy 25°C Only Accuracy 0 A vr Oe Temp erature Average V IOUT –I P (A) vr Oe Temp erature vr Oe Temp erature Decreasing V IOUT(V) IP(min) IP(max) Full Scale |
