ACS712 Allegro MicroSystems, Inc., ACS712 Datasheet - Page 13

• Manufacturer Part Number: ACS712
• Description: Fully Integrated, Hall Effect-based Linear Current Sensor With 2.1 Kvrms Voltage Isolation And A Low-resistance Current Conductor
• Manufacturer: Allegro MicroSystems, Inc.

ACS712
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, ∆V
effect between the resistance of the external filter, R
Application 6), and the input impedance and resistance of the
customer interface circuit, R
resistive divider is given by:
Even if R
resistance values will most likely drift by different amounts over
Application 6. When a low pass filter is constructed
externally to a standard Hall effect device, a resistive
divider may exist between the filter resistor, R
the resistance of the customer interface circuit, R
This resistive divider will cause excessive attenuation,
as given by the transfer function for ∆V
Application 7. Using the FILTER pin
provided on the ACS712 eliminates the
attenuation effects of the resistor divider
between R
cation 6.
F
F
and R
and R
∆V
INTFC
INTFC
ATT
, shown in Appli-
ATT
=
are designed to match, the two individual
V
IOUT
, is a result of the resistive divider
INTFC
⎛
⎜ ⎜
⎝
R
F
R
. The transfer function of this
+ R
ATT
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
INTFC
.
INTFC
F,
and
⎞
⎟
⎠
INTFC
+5 V
Fully Integrated, Hall Effect-Based Linear Current Sensor with
Pin 1
Pin 2
Pin 3
Pin 4
IP+
IP+
IP–
IP–
.
.
Pin 8
F
Hall Current
VCC
Drive
(see
0.1 F
+5 V
IP+
Pin 1 Pin 2
Pin 3 Pin 4
IP–
IP+
IP–
Sense Temperature
Coefficient Trim
Sense
Trim
temperature. Therefore, signal attenuation will vary as a function
of temperature. Note that, in many cases, the input impedance,
R
low as 10 kΩ.
The ACS712 contains an internal resistor, a FILTER pin connec-
tion to the printed circuit board, and an internal buffer amplifier.
With this circuit architecture, users can implement a simple
RC filter via the addition of a capacitor, C
from the FILTER pin to ground. The buffer amplifier inside of
the ACS712 (located after the internal resistor and FILTER pin
connection) eliminates the attenuation caused by the resistive
divider effect described in the equation for ∆V
ACS712 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.
INTFC
Gain
Pin 5
GND
Recovery
Regulator
Voltage
Amp
Signal
, of a typical analog-to-digital converter (ADC) can be as
VCC
Pin 8
Temperature
Coefficient
GND
Pin 5
Trim Control
To all subcircuits
Offset Adjust
0 Ampere
Allegro ACS706
Out
Offset
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
FILTER
VIOUT
Pin 7
Pin 6
N.C.
Pin 6
Low Pass Filter
R
F
C
1 nF
F
C
1 nF
F
Resistive Divider
Buffer Amplifier
and Resistor
F
Allegro ACS712
(see Application 7)
ATT
Application
Input
R
INTFC
Interface
Circuit
. Therefore, the
VIOUT
Pin 7
Input
Application
R
Interface
INTFC
Circuit
13