Thermally Enhanced, Fully Integrated, Hall Effect-Based
High Precision Linear Current Sensor IC with 100 μ Current Conductor
ACS770xCB
22
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Definitions of Accuracy Characteristics
Characteristic Definitions
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 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
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 sensitivity (mV/A) provides the smallest current that the
device is able to resolve.
Nonlinearity (ELIN). The ACS770 is designed to provide a linear
output in response to a ramping current. Consider two current
levels, I1 and I2. Ideally, 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:
E
LINpos = 100 (%) × {1 – (SensIPOS2 / SensIPOS1
) }
E
LINneg = 100 (%) × {1 – (SensINEG2 / SensINEG1
)}
where:
SensIx = (VIOUT(Ix) – VIOUT(Q))/ Ix
and IPOSx and INEGx are positive and negative currents.
Then:
E
LIN = max( ELINpos , ELINneg )
Ratiometry. The device features a ratiometric output. This
means that the quiescent voltage output, VIOUTQ, and the mag-
netic 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(VCC)
V
IOUTQ(5V)
$V
IOUTQ($V)
=s%)
and the ratiometric change (%) in sensitivity is defined as:
VCC 5 V
=s%)
$Sens($V
Sens(VCCSens(V
Quiescent output voltage (VIOUT(Q)). The output of the device
when the primary current is zero. For bidirectional current flow,
it nominally remains at VCC ⁄ 2. Thus, VCC = 5 V translates into
VIOUT(QBI) = 2.5 V. For unidirectional devices, when VCC = 5 V,
VIOUT(QUNI) = 0.5 V. Variation in VIOUT(Q) can be attributed to
the resolution of the Allegro linear IC quiescent 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 for bidirectional
sensor ICs and 0.5 V for unidirectional sensor ICs, due to non-
magnetic 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 material used as a flux concentrator.
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, with-
out the effects of temperature.
0 A over Δ temperature. Accuracy at the zero current flow
including temperature effects.
Full-scale current at 25°C. Accuracy at the full-scale current at
25°C, without the effects of temperature.
Full-scale current over Δ temperature. Accuracy at the full-
scale current flow including temperature effects.
=s%)
ETOT(IP)
VIOUT(IP) – VIOUT_IDEAL(IP)
SensIDEAL sIP
where
VIOUT_IDEAL(IP) = VIOUT(Q) + (SensIDEAL × IP )