Fully Integrated, Hall Effect-Based Linear Current Sensor IC
with 3 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS756
Definitions of Accuracy Characteristics
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
half-scale current of the device.
The ratiometric change (%) in the quiescent voltage output is
defined as:
VIOUTQ(V
VIOUTQ(5V)
)
CC
$VIOUTQ($V)
s ꢀꢁꢁ%
=
VCC
5 V
and the ratiometric change (%) in sensitivity is defined as:
Sens(V
Sens(ꢃVꢂ
ꢂ
CC
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.
$Sens($Vꢂ
s ꢀꢁꢁ%
=
VCC
5 V
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
IOUT(Q) = 2.5 V. Variation in VOUT(Q) can be attributed to the res-
olution of the Allegro linear IC quiescent voltage trim, magnetic
hysteresis, and thermal drift.
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 current. The following equation is used to derive
the linearity:
V
Electrical offset voltage (VOE). The deviation of the device out-
put from its ideal quiescent value of VCC ⁄ 2 due to nonmagnetic
causes.
V
–VIOUT(Q)
Δ gain × % sat (
IOUT_half-scale amperes
2 (VIOUT_quarter-scale amperes –VIOUT(Q)
100
1–
{
[
) [ {
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.
The larger magnetic offsets are observed at the lower operating
temperatures.
)
where
∆ gain = the gain variation as a function of temperature
changes from 25ºC,
% sat = the percentage of saturation of the flux concentra-
tor, which becomes significant as the current being sampled
approaches half-scale ±IP , and
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.
V
IOUT_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 primary current. The following equation is
used to derive symmetry:
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.
VIOUT_+ half-scale amperes –VIOUT(Q)
0 A over Δ temperature. Accuracy at the zero current flow
100
VIOUT(Q) – VIOUT_–half-scale amperes
including temperature effects.
Half-scale current at 25°C. Accuracy at the the half-scale current
at 25°C, without the effects of temperature.
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
Half-scale current over Δ temperature. Accuracy at the half-
.
scale current flow including temperature effects.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
7
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
