ACS715LLCTR-20A-T View Datasheet(PDF) - Allegro MicroSystems

Part Name

Description

MFG CO.

ACS715LLCTR-20A-T

Automotive Grade, Fully Integrated, Hall Effect-Based Linear Current Sensor with 2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor

Allegro MicroSystems 

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ACS715

Automotive Grade, Fully Integrated, Hall Effect-Based Linear Current Sensor

with 2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor

Improving Sensing System Accuracy Using the FILTER Pin

In low-frequency sensing applications, it is often advantageous to

add a simple RC filter to the output of the sensor. Such a low-

pass filter improves the signal-to-noise ratio, and therefore the

resolution, of the sensor output signal. However, the addition of

an RC filter to the output of a sensor IC can result in undesirable

sensor output attenuation — even for dc signals.

Signal attenuation, ∆VATT , is a result of the resistive divider

effect between the resistance of the external filter, RF (see Appli-

cation 5), and the input impedance and resistance of the customer

interface circuit, RINTFC. The transfer function of this resistive

divider is given by:

∆VATT

=

VIOUT

⎜⎜⎝⎛

RINTFC

RF + RINTFC

⎞

⎟⎠

.

Even if RF and RINTFC are designed to match, the two individual

resistance values will most likely drift by different amounts over

temperature. Therefore, signal attenuation will vary as a function

of temperature. Note that, in many cases, the input impedance,

RINTFC , of a typical analog-to-digital converter (ADC) can be as

low as 10 kΩ.

The ACS715 contains an internal resistor, a FILTER pin connec-

tion to the printed circuit board, and an internal buffer ampli-

fier. With this circuit architecture, users can implement a simple

RC filter via the addition of a capacitor, CF (see Application 6)

from the FILTER pin to ground. The buffer amplifier inside of

the ACS715 (located after the internal resistor and FILTER pin

connection) eliminates the attenuation caused by the resistive

divider effect described in the equation for ∆VATT. Therefore, the

ACS715 device is ideal for use in high-accuracy applications that

cannot afford the signal attenuation associated with the use of an

external RC low-pass filter.

Application 5. When a low pass filter is construct-

ed externally to a standard Hall effect device,

a resistive divider may exist between the filter

resistor, RF, and the resistance of the custom-

er interface circuit, RINTFC. This resistive divider

will cause excessive attenuation, as given by the

transfer function for ∆VATT.

+5 V

Pin 3 Pin 4

IP– IP–

0.1 MF

VCC

Pin 8

Allegro ACS706

Voltage

Regulator

To all subcircuits

Amp

Out

Gain

Temperature

Coefficient

Trim Control

Offset

VIOUT

Pin 7

N.C. RF

Pin 6

Resistive Divider

Input

Application

Interface

Circuit

Low Pass Filter

CF

RINTFC

Application 6. Using the FILTER pin

provided on the ACS715 eliminates

the attenuation effects of the resis-

tor divider between RF and RINTFC,

shown in Application 5.

+5 V

IP+ IP+

Pin 1 Pin 2

VCC

Pin 8

GND

Pin 5

IP+

Pin 1

IP+

Pin 2

Hall Current

Drive

IP–

Pin 3

IP–

Pin 4

Sense Temperature

Coefficient Trim

Sense

Trim

Signal

Recovery

0 Ampere

Offset Adjust

GND

Pin 5

Allegro ACS715

Buffer Amplifier

and Resistor

FILTER

Pin 6

CF

VIOUT

Pin 7

Input

Application

Interface

Circuit

RINTFC

Allegro MicroSystems, Inc.

12

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

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