Datasheet ACS756xCB (Allegro) - 7

Fully Integrated, Hall-Effect-Based Linear Current Sensor IC ACS756xCB with 3 kVRMS Voltage Isolation and a Low-Resistance Current Conductor DEFINITIONS OF ACCURACY CHARACTERISTICS Sensitivity (Sens)
The ratiometric change (%) in the quiescent voltage output is defined as: The change in device output in response to a 1 A change through V the primary conductor. The sensitivity is the product of the mag- IOUTQ(VCC) VIOUTQ(5V) ∆VIOUTQ(∆V) = × 100% netic circuit sensitivity (G / A) and the linear IC amplifier gain VCC 5 V (mV/G). The linear IC amplifier gain is programmed at the factory to optimize the sensitivity (mV/A) for the half-scale current of the and the ratiometric change (%) in sensitivity is defined as: device. Sens ∆Sens (VCC) Sens(5V) (∆V) = × 100%
Noise (V
VCC 5 V
NOISE)
The noise floor is derived from the thermal and shot noise
Quiescent Output Voltage (VIOUT(Q))
observed in Hall elements. Dividing the noise (mV) by the sensi- tivity (mV/A) provides the smallest current that the device is able The output of the device when the primary current is zero. For to resolve. a unipolar supply voltage, it nominally remains at VCC ⁄ 2. Thus, VCC = 5 V translates into VIOUT(Q) = 2.5 V. Variation in VOUT(Q)
Nonlinearity (ELIN)
can be attributed to the resolution of the Allegro linear IC quies- cent voltage trim, magnetic hysteresis, and thermal drift. The degree to which the voltage output from the IC varies in direct proportion to the primary current through its half-scale
Electrical Offset Voltage (VOE)
amplitude. Nonlinearity in the output can be attributed to the saturation of the flux concentrator approaching the half-scale cur- The deviation of the device output from its ideal quiescent value rent. The following equation is used to derive the linearity: of VCC ⁄ 2 due to nonmagnetic causes. ∆ gain × % sat ( V )
Magnetic Offset Error (I
100 1– { [ IOUT_half-scale amperes – VIOUT(Q)
ERROM)
2 (VIOUT_quarter-scale amperes – VIOUT(Q) [ { The magnetic offset is due to the residual magnetism (remnant where field) of the core material. The magnetic offset error is highest when the magnetic circuit has been saturated, usually when the ∆ gain = the gain variation as a function of temperature device has been subjected to a full-scale or high-current overload changes from 25°C, condition. The magnetic offset is largely dependent on the mate- % sat = the percentage of saturation of the flux concentra- rial used as a flux concentrator. The larger magnetic offsets are tor, which becomes significant as the current being sampled observed at the lower operating temperatures. approaches half-scale ±IP , and VIOUT_half-scale amperes = the output voltage (V) when the
Total Output Error (ETOT)
sampled current approximates half-scale ±IP . The maximum deviation of the actual output from its ideal value,
Symmetry (E
also referred to as accuracy, illustrated graphically in the output
SYM)
voltage versus current chart on the following page. The degree to which the absolute voltage output from the IC varies in proportion to either a positive or negative half-scale pri- ETOT is divided into four areas: mary current. The following equation is used to derive symmetry: • 0 A at 25°C. Accuracy at the zero current flow at 25°C, V without the effects of temperature. 100 IOUT_+ half-scale amperes – VIOUT(Q) V  IOUT(Q) –VIOUT_–half-scale amperes  • 0 A over Δ temperature. Accuracy at the zero current flow including temperature effects.
Ratiometry
• Half-scale current at 25°C. Accuracy at the the half-scale current The device features a ratiometric output. This means that the qui- at 25°C, without the effects of temperature. escent voltage output, VIOUTQ, and the magnetic sensitivity, Sens, • Half-scale current over Δ temperature. Accuracy at the half-scale are proportional to the supply voltage, VCC. current flow including temperature effects. 7 Allegro MicroSystems 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com