ACS770 datasheet(21/29 Pages) ALLEGRO

21 / 29 page

Thermally Enhanced, Fully Integrated, Hall Effect-Based

High Precision Linear Current Sensor IC with 100 µΩ Current Conductor

ACS770xCB

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 1A 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 ACS770 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 )

RATIOMETRY

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:

VCC 5 V

VIOUTQ(VCC) VIOUTQ(5V)

∆

VIOUTQ(∆V) =

× 100 (%)

and the ratiometric change (%) in sensitivity is defined as:

VCC 5 V

× 100 (%)

∆Sens(∆V)

Sens(VCC)

Sens(5V)

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 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.

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.

• 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.

× 100 (%)

ETOT(IP)

VIOUT(IP) – VIOUT_IDEAL(IP)

SensIDEAL × IP

where

VIOUT_IDEAL(IP) = VIOUT(Q) + (SensIDEAL × IP )

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