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