Not to scale
The ACS70331 is Allegro’s first integrated, high sensitivity,
current sensor IC for <5 A current sensing applications. It
incorporates giant magneto-resistive (GMR) technology that
is 25 times more sensitive than traditional Hall-effect sensors
to sense the magnetic field generated by the current flowing
through the low resistance, integrated primary conductor.
The analog output provides a low noise high-speed signal,
which is proportional to the current flowing through the
primary. The response time of the part is typically 535 ns. The
ACS70331 is offered in four factory-programmed sensitivity
and offset levels to optimize performance over the desired
current measurement range.
The differential configuration of the GMR elements, relative to
the integrated current conductor, provides significant rejection
of stray magnetic fields, resulting in stable operation even in
magnetically noisy environments.
The ACS70331 operates from a single 3.3 V power supply
and is qualified over the full commercial temperature range
of –40°C to 85°C. It is offered in a low-profile, space-saving
surface mount QFN-12 and SOIC-8 packages.
ACS70331-DS, Rev. 3
MCO-0000343
• High sensitivity current sensor IC for sensing
up to 5 A (DC or AC)
• 1 MHz bandwidth with response time <550 ns
• Low noise: 8 mA(rms) at 1 MHz
• Non-ratiometric, analog output proportional to AC and
DC current
• Single 3.3 V supply operation
• High DC PSRR enables use with low accuracy
power supplies or batteries (3 to 4.5 V operation)
• 1.1 mΩ primary conductor resistance results in
low power loss
• Small surface mount QFN-12 and SOIC-8 packages for
space-constrained applications
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
TYPICAL APPLICATION
CBYPASS
0.1 µF
ACS70331
CLOAD
1
2
3
4
10
9
8
5
IP+
IP+
IP–
IP–
VCC
VIOUT
GND
12
6
7
11
NC
NC
NC
NC
NC
IP
ACS70331
VCC
VIOUT
NC
GNDIP -
IP -
IP+
IP+
1
2
3
4
8
7
6
5
CBYPAS
S
0.1 µF
IP
SOIC-8QFN-12
The output, VIOUT, of the ACS70331 responds
proportionally to the current owing through IP.
FEATURES AND BENEFITS DESCRIPTION
PACKAGES
12-contact QFN
3 mm × 3 mm × 0.75 mm
(ES package)
ACS70331
May 17, 2019
8-contact SOIC
(OL package)
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
2
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
SELECTION GUIDE
Part Number Current Sensing
Range, IPR (A)
Sens (Typ)
(mV/A)
TA
(°C) Package Packing [1]
ACS70331EESATR-2P5U3 0 to 2.5 800
–40 to 85
12-contact
QFN with fused
current loop
1500 pieces per reel
ACS70331EESATR-2P5B3 ±2.5 400
ACS70331EESATR-005U3 0 to 5 400
ACS70331EESATR-005B3 ±5 200
ACS70331EOLCTR-2P5U3 0 to 2.5 800
–40 to 85 8-lead SOIC 3000 pieces per reel
ACS70331EOLCTR-2P5B3 ±2.5 400
ACS70331EOLCTR-005U3 0 to 5 400
ACS70331EOLCTR-005B3 ±5 200
[1] Contact Allegro for additional packing options.
ABSOLUTE MAXIMUM RATINGS
Characteristic Symbol Notes Rating Units
Supply Voltage VCC 7 V
Reverse Supply Voltage VRCC –0.1 V
Output Voltage VIOUT 6 V
Reverse Output Voltage VRIOUT –0.1 V
Working Voltage VWORKING
Voltage applied between pins 1 to 4 and pins 5 to 12 (QFN)
or pins 1 to 4 and pins 5 to 8 (SOIC) 100 V
Maximum Continuous Current [2] IP(max) ±10 A
Maximum Continuous External Field [3] B ±50 G
Nominal Operating Ambient Temperature TARange E –40 to 85 °C
Maximum Junction Temperature [2] TJ(max) 100 °C
Storage Temperature Tstg –65 to 125 °C
[2] Continuous currents above this may result in changes in performance. See lifetime drift section for sensor drift under di󰀨erent temperature and current conditions. Also,
see Thermal Performance and Overcurrent Capability section for allowable constant and transient currents.
[3] Continuous magnetic elds above this may result in changes in performance.
[4] The ACS70331 should be soldered using Allegro’s recommended soldering prole in (http://www.allegromicro.com/en/Design-Center/Technical-Documents/Semicon-
ductor-Packaging-Publications/Soldering-Methods-for-Allegro-Products.aspx). Standard soldering tips will over-stress the device, resulting in shifts in performance. For
rework, it is recommended to use hot plates and heat guns/pencils, keeping the temperature of the device below the Maximum Soldering Temperature.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
3
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Terminal List Table
Number Name Description
1, 2 IP+ Terminals for current being sensed; fused internally
3, 4 IP– Terminals for current being sensed; fused internally
5 GND Device ground terminal
6, 8, 9, 11 NC No connection, ground for the best ESD performance
7 NC This pin should be left unconnected during normal operation
10 VIOUT Analog output representing the current flowing through IP
12 VCC Device power supply terminal
Package ES, 12-Pin QFN
Pinout Diagram
PINOUT DIAGRAM AND TERMINAL LIST TABLE
10
9
8
7
1
2
3
4
5
6
12
11
VCC
NC
GND
NC
VIOUT
NC
NC
NC
IP+
IP+
IP–
IP–
Terminal List Table
Number Name Description
1, 2 IP+ Terminals for current being sensed; fused internally
3, 4 IP– Terminals for current being sensed; fused internally
5 GND Device fround terminal
6 NC This pin should be left unconnected during normal operation
7 VIOUT Analog output representing the current flowing through IP
8 VCC Device power supply terminal
Package OL, 8-Pin SOIC
Pinout Diagram
8
7
6
5
1
2
3
4
VCC
VIOUT
NC
GND
IP+
IP+
IP–
IP–
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
4
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
VCC
IP+
IP+
IP–
IP–
VIOUT
GND
Voltage
Regulator Coarse
Gain Trim
Offset
Trim & TC
Sensitivity TC
& Fine Trim
FUNCTIONAL BLOCK DIAGRAM
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
5
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Characteristic Symbol Test Conditions Min. Typ. Max. Unit
ELECTRICAL CHARACTERISTICS
Supply Voltage VCC 3.0 3.3 4.5 V
Supply Current
ICC
VCC(min) ≤ VCC ≤ VCC(max), no load on
VIOUT, fuses powered down – 4.5 6 mA
ICC_START_UP
VCC(min) ≤ VCC ≤ VCC(max), no load on
VIOUT, fuses powered (from time when
VCC rises above VCC(min) to tFPD)
– – 7.5 mA
Primary Conductor Resistance RIP
QFN-12 package, TA = 25°C – 1.1 – mΩ
SOIC-8 package, TA = 25°C – 1.7 – mΩ
Primary Conductor Inductance LIP
QFN-12 package – 1.7 – nH
SOIC-8 package – 4 – nH
Power On Time tPO TA = 25°C – 5 – µs
Fuse Power Down Time [2] tFPD TA = 25°C – 80 120 [3] µs
OUTPUT CHARACTERISTICS
Output Resistive Load RLVIOUT to GND or VIOUT to VCC 22 – – kΩ
Output Capacitive Load CL
VIOUT to GND, output is stable, slew
rate and bandwidth are reduced – – 100 pF
VIOUT to GND, maintains BW – – 50 pF
Source Current ISOURCE TA = 25°C – 0.4 – mA
Sink Current ISINK TA = 25°C – 0.5 – mA
Saturation Voltage [4]
VSAT_HIGH
VCC(min) < VCC < VCC(max);
RL = 22 kΩ to GND 2.8 VCC – 0.15 – V
VSAT_LOW
VCC(min) < VCC < VCC(max);
RL = 22 kΩ to VIOUT – 20 200 mV
Bandwidth BW –3 dB bandwidth – 1 – MHz
Response Time tRESPONSE 1 V swing on VIOUT, 80% to 80% – 535 – ns
Rise Time tr1 V swing on VIOUT, 10% to 90% – 460 – ns
Propagation Delay tpd 1 V swing on VIOUT, 20% to 20% – 220 – ns
Noise Density IND Input referred noise density – 8 – µARMS/
√(Hz)
Noise IN
Input reference noise; TA = 25°C,
Bandwidth = 1 MHz –8 – mARMS
Hysteresis IH
TA = 25°C; change in the output at zero
current after a ±10 A pulse of current
through the sensor
– 10 20 mA
TA = 25°C; change in the output at zero
current after a ±100 A pulse (~20 ms in
duration) of current through the sensor
– 20 – mA
COMMON ELECTRICAL CHARACTERISTICS [1]: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Continued on next page...
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
6
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
COMMON ELECTRICAL CHARACTERISTICS [1] (continued): Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. Max. Unit
Stray Field Sensitivity Error Ratio [5] STERSENS
Measured at 20 G, worst case field
orientation – 0.2 – %/G
Stray Field Offset Error Ratio [5] STEROFF
Measured at 20 G, worst case field
orientation – 3.8 – mA/G
Power Supply Rejection Ratio PSRR
DC to 100 Hz, 100 mV pk-pk on VCC – 40 – dB
100 Hz to 100 kHz, 100 mV pk-pk on
VCC – 30 – dB
Power Supply Offset Error VOE(PS)
Change in offset voltage over
3.0 V < VCC < 4.5 V – ±10 – mV
Power Supply Sensitivity Error ESENS(PS)
Change in sensitivity over
3.0 V < VCC < 4.5 V – ±0.5 – %
Nonlinearity ELIN – ±0.2 – %
[1] Device may be operated at higher ambient, TA, and internal leadframe temperatures, TA, provided that the Maximum Junction Temperature, TJ(max), is not exceeded.
[2] The internal fuses (non-volatile memory used for factory programming) will be powered for tFPD after VCC goes above VCC(min). After this time, the fuse states will have
been saved to volatile memory, and the fuses will be powered down to save power. This means that for tFPD after powering the device, ICC will be around 1 mA higher
than specied (ICC).
[3] This limit is based on simulation and is not tested in production.
[4] See Ideal Output Transfer Curve section.
[5] See Current Sensing Method using GMR and Stray Field Immunity section.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
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Allegro MicroSystems
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www.allegromicro.com
ACS70331EESA-2P5U3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR 0 – 2.5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 800 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 0.25 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±2 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±5 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.5 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±3 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±15 – mV
IP = 0 A, TA = –40°C to 85°C – ±55 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
ACS70331EESA-2P5B3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR –2.5 – 2.5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 400 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 1.5 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±2 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±3 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.5 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±3 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±10 – mV
IP = 0 A, TA = –40°C to 85°C – ±40 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
8
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
ACS70331EESA-005U3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR 0 – 5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 400 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 0.25 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±2 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±3 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.5 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±3 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±10 – mV
IP = 0 A, TA = –40°C to 85°C – ±45 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
ACS70331EESA-005B3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR –5 – 5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 200 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 1.5 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±2 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±3 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.5 – %
Measured at IP = IPR(max), TA = –40°C to 85°C – ±2.5 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±8 – mV
IP = 0 A, TA = –40°C to 85°C – ±45 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
9
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
ACS70331EOLC-2P5U3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR 0 – 2.5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 800 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 0.25 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±2 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±4 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±6.5 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.2 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±4 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±3 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±37 – mV
IP = 0 A, TA = 25°C to 85°C – ±44 – mV
IP = 0 A, TA = –40°C to 25°C – ±100 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
ACS70331EOLC-2P5B3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR –2.5 – 2.5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 400 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 1.5 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±3 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±4.5 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±9 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.1 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±3 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±5.5 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±30 – mV
IP = 0 A, TA = 25°C to 85°C – ±40 – mV
IP = 0 A, TA = –40°C to 25°C – ±70 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
10
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
ACS70331EOLC-005U3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR 0 – 5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 400 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 0.25 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±2.2 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±3.5 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±6.5 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.5 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±3 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±5 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±40 – mV
IP = 0 A, TA = 25°C to 85°C – ±45 – mV
IP = 0 A, TA = –40°C to 25°C – ±100 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
ACS70331EOLC-005B3 PERFORMANCE CHARACTERISTICS: Valid over full range of TA, and VCC = 3.3 V, unless otherwise specied
Characteristic Symbol Test Conditions Min. Typ. [1] Max. Unit
NOMINAL PERFORMANCE [2]
Current Sensing Range IPR –5 – 5 A
Sensitivity Sens IPR(min) < IP < IPR(max) – 200 – mV/A
Zero Current Output Voltage VIOUT(Q) IP = 0 mA, TA = 25°C – 1.5 – V
ACCURACY PERFORMANCE
Total Output Error
[3] ETOT
Measured at IP = IPR(max), TA = 25°C – ±3 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±3 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±6.5 – %
TOTAL OUTPUT ERROR COMPONENTS [4] ETOT = ESENS + 100 × VOE/(Sens × IP)
Sensitivity Error Esens
Measured at IP = IPR(max), TA = 25°C – ±1.3 – %
Measured at IP = IPR(max), TA = 25°C to 85°C – ±2.3 – %
Measured at IP = IPR(max), TA = –40°C to 25°C – ±5.5 – %
Offset Voltage VOE
IP = 0 A, TA = 25°C – ±23 – mV
IP = 0 A, TA = 25°C to 85°C – ±23 – mV
IP = 0 A, TA = –40°C to 25°C – ±50 – mV
[1] Typical values with +/- are 3 sigma values.
[2] See Ideal Output Transfer Curve section.
[3] Percentage of IP
, with IP = IPR(max).
[4] See Lifetime Drift section for accuracy drift under di󰀨erent application temperatures, currents, and elds.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
11
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
THEORY OF OPERATION
GMR Sensing Elements
The ACS70331 uses GMR (giant magneto-resistive) elements
to indirectly measure the current flowing through the package
by measuring the field produced by the current. These elements
operate differently than the Hall-effect sensors used in the major-
ity of Allegro’s current sensors. The main advantage of GMR is
that it is much more sensitive than the Hall-effect, making it ideal
for measuring small currents. This is what enables the ACS70331
to have over 25 times lower input-referred noise than Allegro’s
lowest noise Hall-effect based current sensors. GMR elements are
essentially resistors which change resistance with applied field. A
typical representative response curve for the GMR elements used
in the ACS70331 is shown in Figure 1. It is important to note that
the applied field is parallel to the surface of the sensor instead of
perpendicular to the sensor plane as with planar Hall sensors.
GMR
B
1040
1030
1020
1010
1000
990
980
970
960
-500 -400 -300 -200 -100 0 100 200 300 400 500
Field Applied (G)
R (Ω)
The equation describing this curve is:
() .sin tanRB B
1000 1004 100
1
=- -
b
bl
l
;E
This GMR element has a base resistance of around 1000 Ω that
increases and decreases with field. It is important to note that a
big difference between GMR and the Hall-effect is that GMR
sensors saturate at relatively low fields, limiting the linear operat-
ing region. The linear region of the GMR elements used in the
ACS70331 is around ±50 G.
Figure 1: Typical Response Curve for GMR Elements
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
12
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Current Sensing Method using GMR and
Stray Field Immunity
The internal construction of the ACS70331 QFN package is
shown in Figure 2, and the internal construction of the SOIC-8
package is similar. The die sits above the primary current path
such that magnetic field is produced in plane with the GMR ele-
ments on the die. GMR elements 1 and 2 sense field in the +X
direction for positive IP current flow, and GMR elements 3 and 4
sense field in the –X direction for positive IP current flow. This
enables differential measurement of the current and rejection of
external stray fields.
The four GMR elements are arranged in a Wheatstone bridge
configuration as shown in Figure 3 such that the output of the
bridge is proportional to the differential field sensed by the four
elements, rejecting common fields.
Figure 2: ACS70331 Internal Construction
Figure 3: Wheatstone Bridge Conguration
VCC
IP+
IP+
IP–
IP–
VIOUT
GND
Voltage
Regulator Coarse
Gain Trim
Offset
Trim & TC
Sensitivity TC
& Fine Trim
VREG
GMR3
GMR2
GMR4
GMR1
VBRIDGE
+
–
The output of the bridge will be:
VBRIDGE ∝ VREG × IP × Cf
Here, Cf is the coupling factor from the primary current path to
the GMR elements, which is around 4 G/A.
Theoretically, the bridge configuration will perfectly cancel out all
external common-mode fields that could interfere with the sensor;
however, the performance is limited by non-idealities, such as mis-
match. Typical stray field rejection performance is given in Table
1 for stray fields of 20 G, which is much higher than what will be
seen in most applications. Stray fields in the X direction result in
minimal sensitivity error but some offset error. Stray fields in the
Y direction result in more sensitivity error and less offset error.
Finally, stray fields in the Z direction result in essentially no error,
as the GMR are not sensitive to fields in this dimension.
Table 1: Typical Stray Field Rejection Performance
Field Level (G) Field
Orientation
Typical Sensitivity
Error (%)
Typical Offset
Error (mA)
20 ±X ±4.2 ±76
20 ±Y ±3 15
20 ±Z 0 0
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
13
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Gain and Offset Trim
The bridge configuration of the GMR elements in the ACS70331
make the gain and offset trim for the sensor relatively simple. As
the bridge output voltage is proportional to the voltage driving it,
that voltage is trimmed to compensate for all other nominal gain
errors, as well as errors over temperature. Then, offset is trimmed
out after the bridge voltage has been amplified. All trim codes are
stored using fuses that are programmed at final test before lock-
ing the part.
Ideal Output Transfer Curve
The ideal output of the ACS70331 is:
VIOUT = Sens × IP + VIOUT(Q)
Different versions of the ACS70331 have different sensitivity
(Sens) and zero current output voltage (VIOUT(Q)) values in order
to give different current measurement ranges. Unidirectional
sensors start at 0.25 V with zero current through the primary and
swing +2 V for full-scale current. Bidirectional sensors start at
1.5 V with zero current through the primary and swing ±1 V for
full-scale current. Figure 4 shows the ideal output transfer curves
for each version of the ACS70331. The output curves show the
typical saturation levels; however, the saturation could occur
anywhere beyond the min/max saturation limits shown by the
dashed lines. The stated accuracy of the sensor is only valid over
the given current sensing range (IPR).
3
2.5
2
1.5
1
0.5
0-6 -4 -2 0 2 4 6
IP (A)
VIOUT (V)
2.5 Unidirectional
2.5 Bidirectional
5 Unidirectional
5 Bidirectional
Vsat-high
Vsat-low
Figure 4: Ideal Output Tranfer Curves
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
14
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Power-On Behavior
The power-on behavior of the ACS70331 is shown in Figure 5.
Once VCC goes above VCC(min), it takes tPO for the internal cir-
cuitry to fully power on and bring the output to the correct value.
After tFPD, the ACS70331 has saved the fuse values containing
configuration and trim information to volatile registers and pow-
ered down the fuses to save power. During tFPD, the ACS70331
uses the direct outputs from the fuses, meaning there is no change
in configuration or trim when the fuses are powered down.
VCC
ICC
VIOUT
ICC(typ)
ICC_START_UP
tFPD
tPO
VCC(typ)
VCC(min)
90% VIOUT
Figure 5: Power-On Behavior
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
15
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Frequency and Step Response
The ACS70331 has a bandwidth of approximately 1 MHz.
However, there are a number of poles in the signal path of the
ACS70331, leading to 115 degrees of phase shift at the –3 dB
frequency. The measured frequency response with a 500 mA sine
wave input is shown below.
CHARACTERISTIC PERFORMANCE
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
16
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
The typical step response is shown in the scope capture below.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
17
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Isolation and Transient Voltage Performance
The ACS70331 uses a non-conductive die attach to isolate it from
the primary conductor. This does not provide any level of safety
isolation, as it only passes a hi-pot test of around 500 Vrms. It is
recommended to keep the voltage from the primary to the signal
leads below 100 V during operation.
The construction of the ACS70331 results in there being a
capacitance from the primary conductor to the substrate of the
die. When the voltage on the primary conductor changes rapidly,
this can lead to a perturbation on the output of the sensor. The
scope capture below shows the response of the ACS70331 to a
fast transient voltage on the primary conductor. While the sensor
does get disturbed significantly, it recovers within 0.5 µs due to
the high bandwidth of the sensor.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
18
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Power Supply Rejection Ratio
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
19
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
THERMAL PERFORMANCE AND OVERCURRENT CAPABILITY
The ACS70331 has a small primary conductor resistance of
1.1 mΩ (ES) and 1.7 mΩ (OL), resulting in low power dissipa-
tion and consequently low temperature rise due to current flow
through the sensor. Figure 6 shows the steady-state die temperature
rise versus current of the ACS70331 on the Allegro demo board
(ASEK70331), which has two layers of 1-oz. copper. At 5 A, the
die temperature only rises around 4°C. At 10 A, the die temperature
increases by around 16°C, meaning that at the maximum ambient
temperature of 85°C with the maximum rated continuous current of
10 A flowing, the die would be around its maximum rated junction
temperature of 100°C.
The ACS70331 can also survive higher levels of current that only
last for a short time. Figure 7 shows a curve of the time to fuse
(primary loop fuses open) versus current, which one needs to
operate below.
Figure 6: Change in die temperature versus current
of the ACS70331 on the ASEK70331 demo board (1-
oz. copper) with 22 gauge connectors to the power
supply
Figure 7: Time to fuse versus current of the
ACS70331 on the ASEK70331 demo board (1-oz. cop-
per) and 22 gauge connectors to the power supply
0
2
4
6
8
10
12
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012345678910 11
Change in Die Temperature (°C)
Current (A)
QFN (ES)
SOIC-8 (OL)
10
100
1000
10000
40 60 80 100 120 140 160 180 200
Time To Fuse (ms)
Current (A)
QFN (ES)
SOIC-8 (OL)
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
20
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
GMR elements are made up of thin layers of magnetic material,
and as such, high temperature and magnetic fields can cause
small shifts in the magnetization of those layers, resulting in drift
in the sensor performance. The GMR elements in the ACS70331
are made up of magnetic materials which are relatively immune
to the temperatures and fields seen in most commercial applica-
tions. However, extended times near the maximum rated junction
temperature with applied current or field can cause the gain and
offset of the sensor to shift. These shifts are dependent on the
application temperature, current, and stray field, and typical drift
under various application cases are given in the table below, as
well as a description of the physics behind each drift.
LIFETIME DRIFT
Test Condition Typical Drift (Average + 3 sigma)
Junction
Temperature Current Common Mode
Field Offset Sensitivity
125°C
(408 hours) 0 A 0 G ±140 mA ±0.9%
100°C
(408 hours) 1 A (DC) 0 G ±170 mA ±2.3%
100°C
(408 hours) 2.5 A (DC) 0 G ±210 mA ±1.5%
100°C
(500 hours) 5 A (DC) 0 G ±540 mA ±2.8%
100°C
(408 hours) 5 A (AC) 0 G ±150 mA ±1%
125°C
(48 hours) 0 A 50 G ±150 mA ±1%
C1 Qualification Highest Drift Stress
(Temperature Cycling –40°C to 150°C,
500 cycles)
0 A 0 G ±90 mA ±5%
CASE 1: CONTINUOUS CURRENT AT HIGH
TEMPERATURE
In general, this is the worst case configuration for drift. High
temperature and constant field will slightly rotate some of the
GMR layers. Here, the field seen by two of the GMR elements in
the bridge is in one direction, and the field seen by the other two
GMR elements in the bridge is in the other direction. This results
in two of the elements drifting in one direction and two of them
drifting in the other direction, which causes an offset shift on the
output of the sensor. Typically, at a given temperature and current
there is a maximum amount of shift, and the time constant for
the shift is around 24 hours. If one reverses the current, the shift
will be in the opposite direction. Essentially, at a given tempera-
ture and current level, there is a hysteresis curve for the shift.
The higher the temperature and current, the wider the hysteresis
curve.
CASE 2: AC CURRENT AT HIGH TEMPERATURE
As noted in Case 1, the time constant for the offset shift in
the sensor is around 24 hours, and the shift direction switches
with the current direction. Because of this, AC current tends to
cause little to no shift in the sensor, as the average torque on the
magnetic layers is zero. This is evident in the plot below, which
shows the drift when applying high DC and AC currents at
100°C.
CASE 3: STRAY FIELD AT HIGH TEMPERATURE
When stray field is applied to the sensor at high temperature, all
four resistors in the bridge shift in the same direction, theoreti-
cally cancelling any drift on the output. However, due to mis-
match in the elements, there is still some drift, but it is signifi-
cantly less than what is seen in Case 1 or even Case 2.
High Sensitivity, 1 MHz, GMR-Based Current Sensor IC
in Space-Saving, Low Resistance QFN and SOIC-8 Packages
ACS70331
21
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Hysteresis (IH). The change in the sensor IC zero current output
voltage after being subjected to a large current for a short dura-
tion. Hysteresis is due to slight magnetization of some of the
ferromagnetic layers in GMR. Pulses of current in opposite direc-