ACS712
Fully Integrated, Hall Effect-Based Linear Current Sensor
with 2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
Features and Benefits
Description
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The Allegro® ACS712 provides economical and precise
solutions for AC or DC current sensing in industrial, automotive,
commercial, and communications systems. The device
package allows for easy implementation by the customer.
Typical applications include motor control, load detection and
management, switched-mode power supplies, and overcurrent
fault protection.
Low-noise analog signal path
Device bandwidth is set via the new FILTER pin
5 μs output rise time in response to step input current
50 kHz bandwidth
Total output error 1.5% at TA = 25°C, and 4% at –40°C to 85°C
Small footprint, low-profile SOIC8 package
1.2 mΩ internal conductor resistance
2.1 kVRMS minimum isolation voltage from pins 1-4 to pins 5-8
5.0 V, single supply operation
66 to 185 mV/A output sensitivity
Output voltage proportional to AC or DC currents
Factory-trimmed for accuracy
Extremely stable output offset voltage
Nearly zero magnetic hysteresis
Ratiometric output from supply voltage
The device consists of a precise, low-offset, linear Hall
sensor circuit with a copper conduction path located near the
surface of the die. Applied current flowing through this copper
conduction path generates a magnetic field which is sensed
by the integrated Hall IC and converted into a proportional
voltage. Device accuracy is optimized through the close
proximity of the magnetic signal to the Hall transducer. A
precise, proportional voltage is provided by the low-offset,
chopper-stabilized BiCMOS Hall IC, which is programmed
for accuracy after packaging.
Package: 8 pin SOIC (suffix LC)
The output of the device has a positive slope (>VIOUT(Q))
when an increasing current flows through the primary copper
conduction path (from pins 1 and 2, to pins 3 and 4), which
is the path used for current sensing. The internal resistance of
this conductive path is 1.2 mΩ typical, providing low power
Continued on the next page…
Approximate Scale 1:1
Typical Application
+5 V
1
IP+
VCC
2
IP+ VIOUT
3
IP– FILTER
IP
8
7
VOUT
CBYP
0.1 μF
ACS712
4
IP–
GND
6
5
CF
1 nF
Application 1. The ACS712 outputs an analog signal, VOUT .
that varies linearly with the uni- or bi-directional AC or DC
primary sensed current, IP , within the range specified. CF
is recommended for noise management, with values that
depend on the application.
ACS712-DS, Rev.1
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
Description (continued)
loss. The thickness of the copper conductor allows survival of
the device at up to 5× overcurrent conditions. The terminals of
the conductive path are electrically isolated from the sensor leads
(pins 5 through 8). This allows the ACS712 current sensor to be
used in applications requiring electrical isolation without the use
of opto-isolators or other costly isolation techniques.
The ACS712 is provided in a small, surface mount SOIC8 package.
The leadframe is plated with 100% matte tin, which is compatible
with standard lead (Pb) free printed circuit board assembly processes.
Internally, the device is Pb-free, except for flip-chip high-temperature
Pb-based solder balls, currently exempt from RoHS. The device is
fully calibrated prior to shipment from the factory.
Selection Guide
Part Number
Packing*
TOP
(°C)
Optimized Range, IP
(A)
Sensitivity, Sens
(Typ) (mV/A)
ACS712ELCTR-05B-T
Tape and reel, 3000 pieces/reel
–40 to 85
±5
185
ACS712ELCTR-20A-T
Tape and reel, 3000 pieces/reel
–40 to 85
±20
100
ACS712ELCTR-30A-T
Tape and reel, 3000 pieces/reel
–40 to 85
±30
66
*Contact Allegro for additional packing options.
Absolute Maximum Ratings
Characteristic
Symbol
Notes
Rating
Units
Supply Voltage
VCC
8
V
Reverse Supply Voltage
VRCC
–0.1
V
Output Voltage
VIOUT
8
V
Reverse Output Voltage
VRIOUT
–0.1
V
Output Current Source
IIOUT(Source)
3
mA
IIOUT(Sink)
10
mA
60
A
Output Current Sink
Overcurrent Transient Tolerance
Maximum Transient Sensed Current
Nominal Operating Ambient Temperature
Maximum Junction
Storage Temperature
TÜV America
Certificate Number:
U8V 06 05 54214 010
100 total pulses, 250 ms duration each, applied
at a rate of 1 pulse every 100 seconds.
IP
IR(max)
60
A
–40 to 85
ºC
TJ(max)
165
ºC
Tstg
–65 to 170
ºC
TA
Junction Temperature, TJ < TJ(max)
Range E
Parameter
Specification
Fire and Electric Shock
CAN/CSA-C22.2 No. 60950-1-03
UL 60950-1:2003
EN 60950-1:2001
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
Functional Block Diagram
+5 V
VCC
(Pin 8)
Hall Current
Drive
IP+
(Pin 1)
Sense Temperature
Coefficient Trim
Dynamic Offset
Cancellation
IP+
(Pin 2)
IP−
(Pin 3)
Signal
Recovery
VIOUT
(Pin 7)
RF(INT)
Sense
Trim
IP−
(Pin 4)
0 Ampere
Offset Adjust
GND
(Pin 5)
FILTER
(Pin 6)
Pin-out Diagram
IP+
1
8
VCC
IP+
2
7
VIOUT
IP–
3
6
FILTER
IP–
4
5
GND
Terminal List Table
Number
Name
1 and 2
IP+
Terminals for current being sensed; fused internally
Description
3 and 4
IP–
Terminals for current being sensed; fused internally
5
GND
6
FILTER
7
VIOUT
8
VCC
Signal ground terminal
Terminal for external capacitor that sets bandwidth
Analog output signal
Device power supply terminal
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
COMMON OPERATING CHARACTERISTICS1 over full range of TOP , CF = 1 nF, and VCC = 5 V, unless otherwise specified
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
4.5
5.0
5.5
V
6
8
11
mA
ELECTRICAL CHARACTERISTICS
Supply Voltage
VCC
Supply Current
ICC
VCC = 5.0 V, output open
VZ
ICC = 11 mA, TA = 25°C
6
8.3
–
V
Output Resistance
Output Zener Clamp Voltage
RIOUT
IIOUT = 1.2 mA, TA=25°C
–
1
2
Ω
Output Capacitance Load
CLOAD
VIOUT to GND
–
–
10
nF
Output Resistive Load
RLOAD
VIOUT to GND
4.7
–
–
kΩ
mΩ
Primary Conductor Resistance
RPRIMARY
TA = 25°C
RMS Isolation Voltage
VISORMS
Pins 1-4 and 5-8; 60 Hz, 1 minute, TA=25°C
DC Isolation Voltage
VISODC
tPROP
Propagation Time
Response Time
–
1.2
–
2100
–
–
V
Pins 1-4 and 5-8; 1 minute, TA=25°C
–
5000
–
V
IP = IP(max), TA = 25°C, COUT = open
–
3
–
μs
tRESPONSE IP = IP(max), TA = 25°C, COUT = open
μs
–
7
–
Rise Time
tr
IP = IP(max), TA = 25°C, COUT = open
–
5
–
μs
Frequency Bandwidth
f
–3 dB, TA = 25°C; IP is 10 A peak-to-peak
50
–
–
kHz
Nonlinearity
ELIN
Over full range of IP
–
±1
±1.5
%
Symmetry
ESYM
Over full range of IP
98
100
102
%
Zero Current Output Voltage
VIOUT(Q)
Bidirectional; IP = 0 A, TA = 25°C
–
VCC ×
0.5
–
V
Magnetic Offset Error
VERROM
IP = 0 A, after excursion of 5 A
–
0
–
mV
VCH
Typ. –110
VCC ×
Typ. +110
0.9375
mV
VCL
Typ. –110
VCC ×
Typ. +110
0.0625
mV
Clamping Voltage
Power-On Time
Magnetic
tPO
Output reaches 90% of steady-state level, TJ = 25°C, 20 A present
on leadframe
Coupling2
Internal Filter Resistance3
–
–
RF(INT)
35
–
μs
12
–
G/A
1.7
kΩ
1Device
may be operated at higher primary current levels, IP, and ambient, TA , and internal leadframe temperatures, TOP , provided that the Maximum
Junction Temperature, TJ(max), is not exceeded.
21G = 0.1 mT.
3R
F(INT) forms an RC circuit via the FILTER pin.
COMMON THERMAL CHARACTERISTICS1
Operating Internal Leadframe Temperature
TOP
E range
Min.
Typ.
Max.
–40
–
85
Units
°C
Value
Units
Junction-to-Lead Thermal Resistance2
RθJL
Mounted on the Allegro ASEK 712 evaluation board
5
°C/W
Junction-to-Ambient Thermal Resistance
RθJA
Mounted on the Allegro 85-0322 evaluation board, includes the power consumed by the board
23
°C/W
1Additional
thermal information is available on the Allegro website.
evaluation board has 1500 mm2 of 2 oz. copper on each side, connected to pins 1 and 2, and to pins 3 and 4, with thermal vias connecting the layers. Performance values include the power consumed by the PCB. Further details on the board are available from the Frequently Asked
Questions document on our website. Further information about board design and thermal performance also can be found in the Applications Information section of this datasheet.
2The Allegro
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
ACS712
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
x05A PERFORMANCE CHARACTERISTICS TOP = –40°C to 85°C1, CF = 1 nF, and VCC = 5 V, unless otherwise specified
Characteristic
Optimized Accuracy Range
Sensitivity2
Noise
Symbol
Test Conditions
IP
SensTA
SensTOP
VNOISE(PP)
Over full range of IP, TA = 25°C
Over full range of IP
Min.
Typ.
Max.
–5
–
5
Units
A
–
185
–
mV/A
178
–
193
mV/A
Peak-to-peak, TA= 25°C, 185 mV/A programmed Sensitivity,
CF = 4.7 nF, COUT = open, 20 kHz bandwidth
–
45
–
mV
Peak-to-peak, TA = 25°C, 185 mV/A programmed Sensitivity,
CF = 47 nF, COUT = open, 2 kHz bandwidth
–
20
–
mV
Peak-to-peak, TA = 25°C, 185 mV/A programmed Sensitivity,
CF = 1 nF, COUT = open, 50 kHz bandwidth
–
75
–
mV
–40
–
40
mV
–
±1.5
–
%
Electrical Offset Voltage
VOE
IP = 0 A
Total Output Error3
ETOT
IP =±5 A, TA = 25°C
1Device
may be operated at higher primary current levels, IP, and ambient temperatures, TOP, provided that the Maximum Junction Temperature,
TJ(max), is not exceeded.
2At –40°C Sensitivity may shift as much 9% outside of the datasheet limits.
3Percentage of I , with I = 5 A. Output filtered.
P
P
x20A PERFORMANCE CHARACTERISTICS TOP = –40°C to 85°C1, CF = 1 nF, and VCC = 5 V, unless otherwise specified
Characteristic
Optimized Accuracy Range
Sensitivity2
Noise
Symbol
Test Conditions
Min.
Typ.
Max.
–20
–
20
A
Over full range of IP, TA = 25°C
–
100
–
mV/A
Over full range of IP
97
–
103
mV/A
Peak-to-peak, TA= 25°C, 100 mV/A programmed Sensitivity,
CF = 4.7 nF, COUT = open, 20 kHz bandwidth
–
24
–
mV
Peak-to-peak, TA = 25°C, 100 mV/A programmed Sensitivity,
CF = 47 nF, COUT = open, 2 kHz bandwidth
–
10
–
mV
Peak-to-peak, TA = 25°C, 100 mV/A programmed Sensitivity,
CF = 1 nF, COUT = open, 50 kHz bandwidth
–
40
–
mV
–30
–
30
mV
–
±1.5
–
%
IP
SensTA
SensTOP
VNOISE(PP)
Electrical Offset Voltage
VOE
IP = 0 A
Total Output Error3
ETOT
IP =±20 A, TA = 25°C
Units
1Device
may be operated at higher primary current levels, IP, and ambient temperatures, TOP, provided that the Maximum Junction Temperature,
TJ(max), is not exceeded.
2At –40°C Sensitivity may shift as much 9% outside of the datasheet limits.
3Percentage of I , with I = 20 A. Output filtered.
P
P
x30A PERFORMANCE CHARACTERISTICS TOP = –40°C to 85°C1, CF = 1 nF, and VCC = 5 V, unless otherwise specified
Characteristic
Optimized Accuracy Range
Sensitivity2
Noise
Symbol
Test Conditions
IP
SensTA
SensTOP
VNOISE(PP)
Min.
Typ.
Max.
Units
–30
–
30
A
Over full range of IP , TA = 25°C
–
66
–
mV/A
Over full range of IP
64
–
68
mV/A
Peak-to-peak, TA= 25°C, 66 mV/A programmed Sensitivity,
CF = 4.7 nF, COUT = open, 20 kHz bandwidth
–
20
–
mV
Peak-to-peak, TA = 25°C, 66 mV/A programmed Sensitivity,
CF = 47 nF, COUT = open, 2 kHz bandwidth
–
7
–
mV
Peak-to-peak, TA = 25°C, 66 mV/A programmed Sensitivity,
CF = 1 nF, COUT = open, 50 kHz bandwidth
–
35
–
mV
–30
–
30
mV
–
±1.5
–
%
Electrical Offset Voltage
VOE
IP = 0 A
Total Output Error3
ETOT
IP = ±30 A , TA = 25°C
1Device
may be operated at higher primary current levels, IP, and ambient temperatures, TOP, provided that the Maximum Junction Temperature,
TJ(max), is not exceeded.
2At –40°C Sensitivity may shift as much 9% outside of the datasheet limits.
3Percentage of I , with I = 30 A. Output filtered.
P
P
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
Characteristic Performance
IP = 5 A, Sens = 185 mV/A unless otherwise specified
Mean Supply Current versus Ambient Temperature
Supply Current versus Supply Voltage
VCC = 5 V
10.0
9.0
8.5
ICC (mA)
Mean ICC (mA)
9.5
8.0
7.5
7.0
6.5
6.0
-50
0
50
100
TA (°C)
150
200
10.5
10.3
10.1
9.9
9.7
9.5
9.3
9.1
8.9
8.7
8.5
4.5
Magnetic Offset versus Ambient Temperature
1.25
ELIN (%)
VERROM (mV)
1.50
1.00
0.75
0.50
0.25
0
50
100
TA (°C)
150
4.8
4.9
5
5.1
VCC (V)
5.2
5.3
5.4
5.5
IP = 10 A
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-50
1.75
-50
4.7
Nonlinearity versus Ambient Temperature
2.00
0
4.6
200
0
50
100
TA (°C)
150
200
Mean Total Output Error versus Ambient Temperature
IP = 10 A
Mean ETOT (%)
15.0
10.0
5.0
0.0
-5.0
-10.0
-15.0
-50
0
50
100
TA (°C)
150
Output Voltage versus Sensed Current
Sensitivity versus Sensed Current
4.5
188.0
4.0
VIOUT (V)
TA (°C)
150
85
25
-40
3.0
2.5
2.0
1.5
184.0
TA (°C)
182.0
85
25
-40
180.0
1.0
178.0
0.5
-10
Sens (mV/A)
186.0
3.5
0
200
-8
-6
-4
-2
0
2
Ip (A)
4
6
8
10
176.0
-10
-8
-6
-4
-2
0
2
Ip (A)
4
6
8
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
6
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
Characteristic Performance
IP = 30 A, Sens = 66 mV/A unless otherwise specified
Mean Supply Current versus Ambient Temperature
Supply Current versus Supply Voltage
VCC = 5 V
10.0
9.0
8.5
ICC (mA)
Mean ICC (mA)
9.5
8.0
7.5
7.0
6.5
6.0
-50
0
50
100
TA (°C)
150
200
Magnetic Offset Current versus Ambient Temperature
0.60
ELIN (%)
VERROM (mV)
0.80
0.40
0.20
-50
0
50
100
TA (°C)
150
4.6
4.7
4.8
4.9
5
5.1
VCC (V)
5.2
5.3
5.4
5.5
Nonlinearity versus Ambient Temperature
1.00
0
10.5
10.3
10.1
9.9
9.7
9.5
9.3
9.1
8.9
8.7
8.5
4.5
200
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-50
0
50
100
TA (°C)
150
200
Mean ETOT (%)
Mean Total Output Error versus Ambient Temperature
5.0
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
-50
0
50
100
TA (°C)
150
200
Output Voltage versus Sensed Current
Sensitivity versus Sensed Current
4.5
75.0
VIOUT (V)
3.5
TA (°C)
150
85
25
-40
3.0
2.5
2.0
1.5
1.0
Sens (mV/A)
4.0
70.0
TA (°C)
65.0
85
25
-40
60.0
55.0
0.5
0
-30
-20
-10
0
Ip (A)
10
20
30
50.0
-30
-20
-10
0
Ip (A)
10
20
30
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
7
ACS712
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
Definitions of Accuracy Characteristics
Sensitivity (Sens). The change in sensor 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 programmed at the factory to optimize the sensitivity (mV/A) for the
full-scale current of the device.
Noise (VNOISE). The product of the linear IC amplifier gain
(mV/G) and the noise floor for the Allegro Hall effect linear IC
(≈1 G). 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.
Linearity (ELIN). The degree to which the voltage output from
the sensor varies in direct proportion to the primary current
through its full-scale amplitude. Nonlinearity in the output can be
attributed to the saturation of the flux concentrator approaching
the full-scale current. The following equation is used to derive the
linearity:
{ [
100 1–
Δ gain × % sat ( VIOUT_full-scale amperes – VIOUT(Q) )
2 (VIOUT_half-scale amperes – VIOUT(Q) )
[{
Accuracy is divided into four areas:
• 0 A at 25°C. Accuracy of sensing zero current flow at 25°C,
without the effects of temperature.
• 0 A over Δ temperature. Accuracy of sensing zero current
flow including temperature effects.
• Full-scale current at 25°C. Accuracy of sensing the full-scale
current at 25°C, without the effects of temperature.
• Full-scale current over Δ temperature. Accuracy of sensing fullscale current flow including temperature effects.
Ratiometry. The ratiometric feature means that its 0 A output,
VIOUT(Q), (nominally equal to VCC/2) and sensitivity, Sens, are
proportional to its supply voltage, VCC . The following formula is
used to derive the ratiometric change in 0 A output voltage,
ΔVIOUT(Q)RAT (%).
100
VCC / 5 V
The ratiometric change in sensitivity, ΔSensRAT (%), is defined as:
where VIOUT_full-scale amperes = the output voltage (V) when the
sensed current approximates full-scale ±IP .
100
Symmetry (ESYM). The degree to which the absolute voltage
output from the sensor varies in proportion to either a positive
or negative full-scale primary current. The following formula is
used to derive symmetry:
100
VIOUT(Q)VCC / VIOUT(Q)5V
SensVCC / Sens5V
‰
VCC / 5 V
Output Voltage versus Sensed Current
Accuracy at 0 A and at Full-Scale Current
Increasing VIOUT(V)
Accuracy
Over $Temp erature
VIOUT_+ full-scale amperes – VIOUT(Q)
VIOUT(Q) – VIOUT_–full-scale amperes
Accuracy
25°C Only
Quiescent output voltage (VIOUT(Q)). The output of the sensor
when the primary current is zero. For a unipolar supply voltage,
it nominally remains at VCC ⁄ 2. Thus, VCC = 5 V translates into
VIOUT(Q) = 2.5 V. Variation in VIOUT(Q) can be attributed to the
resolution of the Allegro linear IC quiescent voltage trim and
thermal drift.
Electrical offset voltage (VOE). The deviation of the device output from its ideal quiescent value of VCC / 2 due to nonmagnetic
causes. To convert this voltage to amperes, divide by the device
sensitivity, Sens.
Accuracy (ETOT). The accuracy represents the maximum deviation of the actual output from its ideal value. This is also known
as the total ouput error. The accuracy is illustrated graphically in
the output voltage versus current chart at right.
Average
VIOUT
Accuracy
Over $Temp erature
Accuracy
25°C Only
IP(min)
–IP (A)
+IP (A)
Full Scale
IP(max)
0A
Accuracy
25°C Only
Accuracy
Over $Temp erature
Decreasing VIOUT(V)
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
8
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
Definitions of Dynamic Response Characteristics
Primary Current
I (%)
Propagation delay (tPROP). The time required for the sensor
output to reflect a change in the primary current signal. Propagation delay is attributed to inductive loading within the linear IC
package, as well as in the inductive loop formed by the primary
conductor geometry. Propagation delay can be considered as a
fixed time offset and may be compensated.
90
Transducer Output
0
t
Propagation Time, tPROP
Primary Current
I (%)
Response time (tRESPONSE). The time interval between
a) when the primary current signal reaches 90% of its final
value, and b) when the sensor reaches 90% of its output
corresponding to the applied current.
90
Transducer Output
0
Response Time, tRESPONSE
tPO (μs)
Rise time (tr). The time interval between a) when the sensor
reaches 10% of its full scale value, and b) when it reaches 90%
of its full scale value. The rise time to a step response is used to
derive the bandwidth of the current sensor, in which ƒ(–3 dB) =
0.35 / tr. Both tr and tRESPONSE are detrimentally affected by eddy
current losses observed in the conductive IC ground plane.
Primary Current
I (%)
90
Transducer Output
10
0
t
Rise Time, tr
Step Response
Power on Time versus External Filter Capacitance
200
180
160
140
120
100
80
60
40
20
0
t
TA=25°C
IP =5 A
IP =0 A
0
10
20
CF (nF)
30
40
Output (mV)
50
Noise vs. Filter Cap
15 A
Noise versus External Filter Capacitance
10000
Excitation Signal
100
10
1
0.01
0.1
1
CF (nF)
10
100
1000
tr(μs)
Rise Time versus External Filter Capacitance
1200
CF (nF)
1000
0
1
4.7
10
22
47
100
220
470
800
600
400
}
Expanded in chart at right
200
0
0
100
200
300
CF (nF)
400
500
tr (μs)
6.6
7.7
17.4
32.1
68.2
88.2
291.3
623.0
1120.0
Rise Time versus External Filter Capacitance
400
350
tr(μs)
Noise(p-p) (mA)
1000
300
250
200
150
0
0
50
75
100
125
150
CF (nF)
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
9
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
Chopper Stabilization Technique
This technique is made possible through the use of a BiCMOS
process that allows the use of low-offset and low-noise amplifiers
in combination with high-density logic integration and sample
and hold circuits.
Regulator
Clock/Logic
Low-Pass
Filter
Hall Element
Sample and
Hold
Chopper Stabilization is an innovative circuit technique that is
used to minimize the offset voltage of a Hall element and an associated on-chip amplifier. Allegro patented a Chopper Stabilization technique that nearly eliminates Hall IC output drift induced
by temperature or package stress effects. This offset reduction
technique is based on a signal modulation-demodulation process.
Modulation is used to separate the undesired dc offset signal from
the magnetically induced signal in the frequency domain. Then,
using a low-pass filter, the modulated dc offset is suppressed
while the magnetically induced signal passes through the filter.
As a result of this chopper stabilization approach, the output
voltage from the Hall IC is desensitized to the effects of temperature and mechanical stress. This technique produces devices that
have an extremely stable Electrical Offset Voltage, are immune to
thermal stress, and have precise recoverability after temperature
cycling.
Amp
Concept of Chopper Stabilization Technique
Typical Applications
+5 V
+5 V
VPEAK
CBYP
0.1 μF
1
2
IP
IP+
VCC
IP+ VIOUT
4
7
RF
10 kΩ
IP– FILTER
IP–
COUT
0.1 μF
VOUT
8
ACS712
3
CBYP
0.1 μF
C2
0.1 μF
GND
6
5
R4
10 kΩ
Q1
2N7002
1
+
2
–
D1
U1
LT1178 1N914
R1
1 MΩ
CF
1 nF
IP
4
R2
33 kΩ
C1
0.1 μF
VCC
IP+
IP+ VIOUT
R2
100 kΩ
8
7
IP– FILTER
IP–
1
+
3
–
GND
VOUT
4
2
C1
1000 pF
R3
3.3 kΩ
6
CF
0.01 μF
5
LM321
5
RF
1 kΩ
ACS712
3
R3
330 kΩ
R1
100 kΩ
VRESET
Application 3. This configuration increases gain to 610 mV/A
(tested using the ACS712ELC-05A).
Application 2. Peak Detecting Circuit
+5 V
+5 V
CBYP
0.1 μF
R1
33 kΩ
CBYP
0.1 μF
1
2
IP+
VCC
IP+ VIOUT
8
7
RF
2 kΩ
ACS712
IP
3
4
IP– FILTER
IP–
GND
VOUT
6
5
R1
10 kΩ
CF
1 nF
D1
1N4448W
1
2
A-to-D
Converter
IP
C1
Application 4. Rectified Output. 3.3 V scaling and rectification application
for A-to-D converters. Replaces current transformer solutions with simpler
ACS circuit. C1 is a function of the load resistance and filtering desired.
R1 can be omitted if the full range is desired.
IP+
VCC
IP+ VIOUT
8
7
VOUT
4
IP– FILTER
IP–
GND
4
3
ACS712
3
RPU
100 kΩ
R2
100 kΩ
6
5
CF
1 nF
–
+
5
1
Fault
2 U1
LMV7235
D1
1N914
Application 5. 10 A Overcurrent Fault Latch. Fault threshold set by R1 and
R2. This circuit latches an overcurrent fault and holds it until the 5 V rail is
powered down.
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
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 lowpass 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
Application 6), and the input impedance and resistance of the
customer interface circuit, RINTFC. The transfer function of this
resistive divider is given by:
⎛
RINTFC
⎝
RF + RINTFC
∆VATT = VIOUT ⎜
⎜
⎞
⎟
⎠
.
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 ACS712 contains an internal resistor, a FILTER pin connection 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, CF (see Application 7)
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 ∆VATT. Therefore, the
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.
+5 V
Pin 3 Pin 4
IP–
IP–
VCC
Pin 8
Allegro ACS706
Voltage
Regulator
To all subcircuits
Filter
0.1 MF
Resistive Divider
VIOUT
Pin 7
Dynamic Offset
Cancellation
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, RF, and
the resistance of the customer interface circuit, RINTFC.
This resistive divider will cause excessive attenuation,
as given by the transfer function for ∆VATT.
Amp
Out
N.C.
Pin 6
Input
RF
Application
Interface
Circuit
Low Pass Filter
Temperature
Coefficient
Gain
Offset
CF
1 nF
RINTFC
Trim Control
GND
Pin 5
IP+
IP+
Pin 1 Pin 2
+5 V
VCC
Pin 8
Allegro ACS712
Hall Current
Drive
IP+
Pin 1
IP+
Pin 2
IP–
Pin 3
IP–
Pin 4
Sense Temperature
Coefficient Trim
Buffer Amplifier
and Resistor
Dynamic Offset
Cancellation
Application 7. Using the FILTER pin
provided on the ACS712 eliminates the
attenuation effects of the resistor divider
between RF and RINTFC, shown in Application 6.
Signal
Recovery
VIOUT
Pin 7
Input
Application
Interface
Circuit
Sense
Trim
0 Ampere
Offset Adjust
RINTFC
GND
Pin 5
FILTER
Pin 6
CF
1 nF
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Fully Integrated, Hall Effect-Based Linear Current Sensor with
2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor
ACS712
Package LC, 8-pin SOIC
6.20 .244
5.80 .228
0.25 [.010] M B M
5.00 .197
4.80 .189
8º
0º
A
B
8
0.25 .010
0.17 .007
Preliminary dimensions, for reference only
Dimensions in millimeters
U.S. Customary dimensions (in.) in brackets, for reference only
(reference JEDEC MS-012 AA)
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
A Terminal #1 mark area
4.00 .157
3.80 .150
1.27 .050
0.40 .016
A
1
2
0.25 .010
8X
8X
0.51 .020
0.31 .012
0.25 .010
0.10 .004
1.27 .050
ACS712T
RLCPPP
YYWWA
ACS
712
T
R
LC
PPP
YY
WW
A
2
Text 1
Text 2
Text 3
Two alternative patterns are used
1
SEATING PLANE
GAUGE PLANE
1.75 .069
1.35 .053
0.25 [.010] M C A B
Package Branding
C
SEATING
PLANE
0.10 [.004] C
8
7
3
6
4
5
Allegro Current Sensor
Device family number
Indicator of 100% matte tin leadframe plating
Operating ambient temperature range code
Package type designator
Primary sensed current
Date code: Calendar year (last two digits)
Date code: Calendar week
Date code: Shift code
The products described herein are manufactured under one or more
of the following U.S. patents: 5,045,920; 5,264,783; 5,442,283;
5,389,889; 5,581,179; 5,517,112; 5,619,137; 5,621,319; 5,650,719;
5,686,894; 5,694,038; 5,729,130; 5,917,320; and other patents
pending.
Allegro MicroSystems, Inc. reserves the right to make, from time
to time, such departures from the detail specifications as may be
required to permit improvements in the performance, reliability,
ACS712T
RLCPPP
L...L
YYWW
ACS
712
T
R
LC
PPP
L...L
YY
WW
Allegro Current Sensor
Device family number
Indicator of 100% matte tin leadframe plating
Operating ambient temperature range code
Package type designator
Primary sensed current
Lot code
Date code: Calendar year (last two digits)
Date code: Calendar week
or manufacturability of its products. Before placing an order,
the user is cautioned to verify that the information being relied
upon is current. The information included herein is believed to
be accurate and reliable. However, Allegro MicroSystems, Inc.
assumes no responsibility for its use; nor for any infringement of
patents or other rights of third parties which may result from its
use.
Copyright ©2006, Allegro MicroSystems, Inc.
For the latest version of this document, go to our website at:
www.allegromicro.com
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com