High Accuracy, Hall-Effect-Based, 200 kHz Bandwidth,
Galvanically Isolated Current Sensor IC with 100 µΩ Current Conductor
ACS773
17
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Definitions of Accuracy Characteristics
CHARACTERISTIC DEFINITIONS
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 amplifier gain is
programmed at the factory to optimize the sensitivity (mV/A) for
the full-scale current of the device.
SENSITIVITY ERROR (ESens)
The sensitivity error is the percent difference between the mea-
sured sensitivity and the ideal sensitivity. For example, in the case
of VCC = 3.3 V:
=× 100 (%)
ESens
SensMeas(3.3V) – SensIdeal(3.3V)
SensIDEAL(3.3V)
NOISE (VN)
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 ACS773 is designed to provide a linear output in response
to a ramping current. Consider two current levels: I1 and I2. Ide-
ally, the sensitivity of a device is the same for both currents, for
a given supply voltage and temperature. Nonlinearity is present
when there is a difference between the sensitivities measured at
I1 and I2. Nonlinearity is calculated separately for the positive
(ELINpos ) and negative (ELINneg ) applied currents as follows:
ELINpos = 100 (%) × {1 – (SensIPOS2 / SensIPOS1
) }
ELINneg = 100 (%) × {1 – (SensINEG2 / SensINEG1
)}
where:
SensIx = (VIOUT(Ix) – VIOUT(Q))/ Ix
and IPOSx and INEGx are positive and negative currents.
Then:
ELIN = max( ELINpos , ELINneg )
SYMMETRY (ESYM)
The degree to which the absolute voltage output from the IC var-
ies in proportion to either a positive or negative half-scale primary
current. The following equation is used to derive symmetry:
100 ×
VIOUT_+half-scale amperes – VIOUT(Q)
V
– V
RATIOMETRY ERROR
The device features a ratiometric output. This means that the
quiescent 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:
RatErrQVO = (VIOUTQ(VCC) / VIOUTQ(3.3V))
VCC / 3.3 V × 100%
[ ]
1 –
and the ratiometric change (%) in sensitivity is defined as:
RatErrSens = 1 – (Sens(VCC) / Sense(3.3V))
VCC / 3.3 V × 100%
ZERO CURRENT OUTPUT VOLTAGE (VIOUT(Q))
The output of the sensor when the primary current is zero. It
nominally remains 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.
ELECTRICAL 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 voltage to amperes, divide by
the device sensitivity, Sens.
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.