ACS709
Description
The Allegro® ACS709 current sensor IC provides economical
and precise means for current sensing applications in industrial,
automotive, commercial, and communications systems. The
device is offered in a small footprint surface mount package
that allows easy implementation in customer applications.
The ACS709 consists of a precision linear Hall sensor integrated
circuit with a copper conduction path located near the surface
of the silicon die. Applied current flows through the copper
conduction path, and the analog output voltage from the Hall
sensor IC linearly tracks the magnetic field generated by the
applied current. The accuracy of the ACS709 is maximized
with this patented packaging configuration because the Hall
element is situated in extremely close proximity to the current
to be measured.
High level immunity to current conductor dV/dt and stray
electric fields, offered by Allegro proprietary integrated shield
technology, guarantees low output ripple and low offset drift
in high-side applications.
The voltage on the Overcurrent Input (VOC pin) allows
customers to define an overcurrent fault threshold for the
device. When the current flowing through the copper conduction
path (between the IP+ and IP– pins) exceeds this threshold,
ACS709-DS, Rev. 2
Features and Benefits
Industry-leading noise performance with 120 kHz
bandwidth through proprietary amplifier and filter
design techniques
Integrated shield greatly reduces capacitive coupling
from current conductor to die due to high dV/dt, and
prevents offset drift in high-side applications
Small footprint surface mount QSOP24 package
2100 VRMS isolation voltage between primary current
path and sensor IC electronics
1.1 m primary conductor resistance for low power loss
User-settable Overcurrent Fault level
Overcurrent Fault signal typically responds to an
overcurrent condition in < 2 s
Filter pin capacitor sets analog signal bandwidth
±2% typical output error
3 to 5.5 V, single supply operation
Factory trimmed sensitivity, quiescent output voltage,
and associated temperature coefficients
Chopper stabilization results in extremely stable
quiescent output voltage
Ratiometric output from supply voltage
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
Continued on the next page…
Typical Application
RH, RLSets resistor divider reference for VOC
CFNoise and bandwidth limiting filter capacitor
COC Fault delay setting capacitor, 22 nF maximum
AUse of capacitor required
BUse of resistor optional
Package: 24 pin QSOP (suffix LF)
Approximate Scale
1
2
3
4
5
6
7
8
9
10
11
12
IP+
IP+
IP+
IP+
IP+
IP+
IP–
IP–
IP–
IP–
IP–
IP–
22
21
20
19
18
17
16
15
NC
NC
FAULT_EN
VOC
VCC
FAULT
VIOUT
FILTER
VZCR
GND
NC
NC
ACS709
0.1 F
COC
CF
330 k
1 nF
VIOUT
Fault_EN
VCC
RH
RL
IPB
A
24
23
14
13
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Selection Guide
Part Number IP(LIN)
(A)
Sens
(Typ at VCC = 5 V)
(mV/A)
TA
(°C) Packing*
ACS709LLFTR-35BB-T 75 28 –40 to 150 Tape and Reel, 2500 pieces per reel
ACS709LLFTR-20BB-T 37.5 56
*Contact Allegro for packing options.
the open drain Overcurrent Fault pin will transition to a logic low
state. Factory programming of the linear Hall sensor IC inside of
the ACS709 results in exceptional accuracy in both analog and
digital output signals.
The internal resistance of the copper path used for current sensing is
typically 1.1 m, for low power loss. Also, the current conduction
path is electrically isolated from the low voltage device inputs and
outputs. This allows the ACS709 family of sensor ICs to be used
in applications requiring electrical isolation, without the use of
opto-isolators or other costly isolation techniques.
Applications include:
• Motor control and protection
• Load management and overcurrent detection
• Power conversion and battery monitoring / UPS systems
Description (continued)
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Units
Supply Voltage VCC 8V
Filter Pin VFILTER 8V
Analog Output Pin VIOUT 32 V
Overcurrent Input Pin VOC 8V
Overcurrent ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯
Pin V ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯ 8V
Fault Enable (FAULT_EN) Pin VFAULTEN 8V
Voltage Reference Output Pin VZCR 8V
DC Reverse Voltage: Supply Voltage, Filter, Analog
Output, Overcurrent Input, Overcurrent Fault, Fault
Enable, and Voltage Reference Output Pins
VRdcx –0.5 V
Rated Dielectric Insulation Voltage VISO 60 Hz AC, 1 minute at TA = 25°C 2100 VAC
Rated Continuous Voltage on Primary Leads
(IP+ and IP–) VWORKING
For single protection according to UL 1577 standard; for
higher continuous voltage ratings, please contact Allegro 277 VAC
Output Current Source IIOUT(Source) 3mA
Output Current Sink IIOUT(Sink) 1mA
Operating Ambient Temperature TARange L –40 to 150 °C
Junction Temperature TJ(max) 165 °C
Storage Temperature Tstg –65 to 170 °C
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
IP–
VZCR
FILTERGND
VIOUT
Drain
IP+
FAULT
Signal
Recovery
V
OUT(Q)
Trim
Sensitivity
Trim
R
Q
CLK
D
VOC
VCC
POR
FAULT Reset
3 mA
2V
REF
POR
Hall
Bias
Control
Logic
FAULT_EN
+
–
+
–
Fault
Comparator
Hall
Amplifier
R
F(INT)
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
IP+
IP+
IP+
IP+
IP+
IP+
IP–
IP–
IP–
IP–
IP–
IP–
NC
NC
FAULT_EN
VOC
VCC
FAULT
VIOUT
FILTER
VZCR
GND
NC
NC
Terminal List Table
Number Name Description
1 through 6 IP+ Sensed current copper conduction path pins. Terminals for current being sensed;
fused internally, loop to IP– pins; unidirectional or bidirectional current flow.
7 through 12 IP– Sensed current copper conduction path pins. Terminals for current being sensed;
fused internally, loop to IP+ pins; unidirectional or bidirectional current flow.
13, 14, 23, 24 NC No connection
15 GND Device ground connection.
16 VZCR Voltage Reference Output pin. Zero current (0 A) reference; output voltage on this
pin scales with VCC
.
17 FILTER Filter pin. Terminal for an external capacitor connected from this pin to GND to set
the device bandwidth.
18 VIOUT Analog Output pin. Output voltage on this pin is proportional to current flowing
through the loop between the IP+ pins and IP– pins.
19 ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯ Overcurrent Fault pin. When current flowing between IP+ pins and IP– pins
exceeds the overcurrent fault threshold, this pin transitions to a logic low state.
20 VCC Supply voltage.
21 VOC Overcurrent Input pin. Analog input voltage on this pin sets the overcurrent fault
threshold.
22 FAULT_EN Enables overcurrent faulting when high. Resets ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯
when low.
Functional Block Diagram
Pin-out Diagram
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
COMMON OPERATING CHARACTERISTICS Valid at TA = –40°C to 150°C, VCC
= 5 V, unless otherwise specified
Characteristic Symbol Test Conditions Min. Typ. Max. Units
ELECTRICAL CHARACTERISTICS
Supply Voltage1VCC 3 – 5.5 V
Nominal Supply Voltage VCCN –5–V
Supply Current ICC VIOUT open, ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯
pin high – 11 14.5 mA
Output Capacitance Load CLOAD VIOUT pin to GND – – 10 nF
Output Resistive Load RLOAD VIOUT pin to GND 10 – – k
Magnetic Coupling from Device Conductor
to Hall Element MCHALL Current flowing from IP+ to IP– pins – 9.5 – G/A
Internal Filter Resistance2RF(INT) – 1.7 – k
Primary Conductor Resistance RPRIMARY TA = 25°C – 1.1 – m
ANALOG OUTPUT SIGNAL CHARACTERISTICS
Full Range Linearity3ELIN IP = ±IP0A –0.75 ±0.25 0.75 %
Symmetry4ESYM IP = ±IP0A 99.1 100 100.9 %
Bidirectional Quiescent Output VOUT(QBI) IP = 0 A, TA = 25°C – VCC×0.5 – V
TIMING PERFORMANCE CHARACTERISTICS
VIOUT Signal Rise Time tr
TA = 25°C, Swing IP from 0 A to IP0A,
no capacitor on FILTER pin, 100 pF from
VIOUT to GND
–3–s
VIOUT Signal Propagation Time tPROP
TA = 25°C, no capacitor on FILTER pin,
100 pF from VIOUT to GND –1–s
VIOUT Signal Response Time tRESPONSE
TA = 25°C, Swing IP from 0 A to IP0A,
no capacitor on FILTER pin, 100 pF from
VIOUT to GND
–4–s
VIOUT Large Signal Bandwidth5f3dB
–3 dB, TA = 25°C, no capacitor on FILTER
pin, 100 pF from VIOUT to GND – 120 – kHz
Power-On Time tPO
Output reaches 90% of steady-state level,
no capacitor on FILTER pin, TA = 25°C –35–s
OVERCURRENT CHARACTERISTICS
Setting Voltage for Overcurrent Switchpoint6VOC VCC×0.25 – VCC×0.4 V
Signal Noise at Overcurrent
Comparator Input INCOMP –±1–A
Overcurrent Fault Switchpoint Error7,8 EOC
Switchpoint in VOC safe operating area;
assumes INCOMP = 0 A –±5–%
Overcurrent ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯
Pin Output Voltage V ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯ 1 mA sink current at ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯
pin – – 0.4 V
Fault Enable (FAULT_EN Pin) Input Low
Voltage Threshold VIL – – 0.1 × VCC V
Fault Enable (FAULT_EN Pin) Input High
Voltage Threshold VIH 0.8 × VCC ––V
Fault Enable (FAULT_EN Pin) Input
Resistance RFEI –1–M
Continued on the next page…
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OVERCURRENT CHARACTERISTICS (continued)
Fault Enable (FAULT_EN Pin) Delay9tFED
Set FAULT_EN to low, VOC = 0.25 × VCC
,
COC = 0 F; then run a DC IP exceeding the
corresponding overcurrent threshold; then
reset FAULT_EN from low to high and
measure the delay from the rising edge of
FAULT_EN to the falling edge of ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯
–15–s
Overcurrent Fault Response Time tOC
FAULT_EN set to high for a minimum
of 20 s before the overcurrent event;
switchpoint set at VOC = 0.25 × VCC
;
delay from IP exceeding overcurrent
fault threshold to V ¯
F
¯
¯
A
¯
U ¯¯
L
¯
¯
T
¯
< 0.4 V, without
external COC capacitor
– 1.9 – s
Overcurrent Fault Reset Delay tOCR
Time from VFAULTEN < VIL to
VFAULT > 0.8 × VCC , RPU = 330 k– 500 – ns
Overcurrent Fault Reset Hold Time tOCH
Time from VFAULTEN pin < VIL to reset of
fault latch; see Functional Block Diagram – 250 – ns
Overcurrent Input Pin Resistance ROC TA = 25°C, VOC pin to GND 2 – – M
VOLTAGE REFERENCE CHARACTERISTICS
Voltage Reference Output VZCR TA = 25 °C – 0.5 × VCC –V
Voltage Reference Output Load Current IZCR
Source current 3 – – mA
Sink current 50 – – A
Voltage Reference Output Drift VZCR – ±10 – mV
1Devices are trimmed for maximum accuracy at VCC = 5 V. The ratiometry feature of the device allows operation over the full VCC range; however, accuracy
may be slightly degraded for VCC values other than 5 V. Contact the Allegro factory for applications that require maximum accuracy for VCC = 3.3 V.
2RF(INT) forms an RC circuit via the FILTER pin.
3This parameter can drift by as much as 0.25% over the lifetime of this product.
4This parameter can drift by as much as 0.3% over the lifetime of this product.
5Calculated using the formula f3dB = 0.35 / tr
.
6See page 8 on how to set overcurrent fault switchpoint.
7Switchpoint can be lower at the expense of switchpoint accuracy.
8This error specification does not include the effect of noise. See the INCOMP specification in order to factor in the additional influence of noise on the
fault switchpoint.
9Fault Enable Delay is designed to avoid false tripping of an Overcurrent (OC) fault at power-up. A 15 s (typical) delay will always be needed, every
time FAULT_EN is raised from low to high, before the device is ready for responding to any overcurrent event.
COMMON OPERATING CHARACTERISTICS (continued) Valid at TA = –40°C to 150°C, VCC
= 5 V, unless otherwise specified
Characteristic Symbol Test Conditions Min. Typ. Max. Units
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
X35B PERFORMANCE CHARACTERISTICS, TA Range L, valid at TA = – 40°C to 150°C, VCC = 5 V, unless otherwise specified
Characteristic Symbol Test Conditions Min. Typ. Max. Units
Optimized Accuracy Range IP(OA) –37.5 – 37.5 A
Linear Sensing Range IP(LIN) –75 – 75 A
Performance Characteristics at VCC = 5 V
Noise1VNOISE(rms) TA = 25°C, Sens = 28 mV/A, Cf = 0, CLOAD = 4.7 nF, RLOAD open – 1 – mV
Sensitivity2,3 Sens
IP = 25 A, TA = 25°C – 28 – mV/A
IP = 25 A, TA = 25°C to 150°C 27 – 29.5 mV/A
IP = 25 A, TA = – 40°C to 25°C 27 – 29.5 mV/A
Electrical Offset Voltage2VOE
IP = 0 A, TA = 25°C – ±5 – mV
IP = 0 A, TA = 25°C to 150°C –25 – 25 mV
IP = 0 A, TA = – 40°C to 25°C –40 – 40 mV
Total Output Error2,4 ETOT
Tested at IP = 25 A , IP applied for 5 ms, TA = 25°C to 150°C – ±3 – %
Tested at IP = 25 A , IP applied for 5 ms, TA = – 40°C to 25°C – ±3 – %
1Vpk-pk noise (6 sigma noise) is equal to 6 × VNOISE(rms). Lower noise levels than this can be achieved by using Cf for applications requiring narrower
bandwidth. See Characteristic Performance page for graphs of noise versus Cf and bandwidth versus Cf.
2See Characteristic Performance Data graphs for parameter distribution over ambient temperature range.
3This parameter can drift by as much as 1.75% over lifetime of the product.
4This parameter can drift by as much as 2.5% over lifetime of the product.
X20B PERFORMANCE CHARACTERISTICS, TA Range L, valid at TA = – 40°C to 150°C, VCC = 5 V, unless otherwise specified
Characteristic Symbol Test Conditions Min. Typ. Max. Units
Optimized Accuracy Range IP(OA) –20 – 20 A
Linear Sensing Range IP(LIN) –37.5 – 37.5 A
Performance Characteristics at VCC = 5 V
Noise1VNOISE(rms) TA = 25°C, Sens = 56 mV/A, Cf = 0, CLOAD = 4.7 nF, RLOAD open – 1.50 – mV
Sensitivity2,3 Sens
IP = 12.5 A, TA = 25°C – 56 – mV/A
IP = 12.5 A, TA = 25°C to 150°C 54.5 – 58 mV/A
IP = 12.5 A, TA = – 40°C to 25°C 54.5 – 58.5 mV/A
Electrical Offset Voltage2VOE
IP = 0 A, TA = 25°C – ±5 – mV
IP = 0 A, TA = 25°C to 150°C –25 – 25 mV
IP = 0 A, TA = – 40°C to 25°C –40 – 40 mV
Total Output Error2,4 ETOT
Tested at IP =12.5 A , IP applied for 5 ms, TA = 25°C to 150°C – ±2 – %
Tested at IP =12.5 A , IP applied for 5 ms, TA = – 40°C to 25°C – ±3 – %
1Vpk-pk noise (6 sigma noise) is equal to 6 × VNOISE(rms). Lower noise levels than this can be achieved by using Cf for applications requiring narrower
bandwidth. See Characteristic Performance page for graphs of noise versus Cf and bandwidth versus Cf.
2See Characteristic Performance Data graphs for parameter distribution over ambient temperature range.
3This parameter can drift by as much as 1.75% over lifetime of the product.
4This parameter can drift by as much as 2.5% over lifetime of the product.
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Thermal Characteristics
Characteristic Symbol Test Conditions Value Units
Steady State Package Thermal Resistance RJA
Tested with 30 A DC current and based on ACS709 demo
board in 1 cu. ft. of still air. Please refer to product FAQs
page on Allegro web site for detailed information on
ACS709 demo board.
21 ºC/W
Transient Package Thermal Resistance RTJA
Tested with 30 A DC current and based on ACS709 demo
board in 1 cu. ft. of still air. Please refer to product FAQs
page on Allegro web site for detailed information on
ACS709 demo board.
See graph ºC/W
0
2
4
6
8
10
12
14
16
18
20
22
0.01 0.1 1 10 100 1000
Thermal Resistance (°C/W)
Time (Sec)
ACS709 Transient Package Thermal Resistance
On 85--0444 Demo Board (No Al Plate)
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ACS709 Bandwidth versus External Capacitor Value, CF
Capacitor connected between FILTER pin and GND
1000
100
10
1
0.1
0.01 0.1 1 10 100 1000
Bandwidth (kHz)
Capacitance (nF)
Characteristic Performance
ACS709x-35B
V
CC
= 5 V
ACS709x-35B
V
CC
= 3.3 V
ACS709x-20B
V
CC
= 5 V
ACS709x-20B
V
CC
= 3.3 V
Capacitance (nF)
Capacitance (nF)
Capacitance (nF)
Capacitance (nF)
RM S Nois e (V)
RM S Nois e (V)
RM S Nois e (V)
RM S Nois e (V)
400
500
600
700
800
900
10 0 0
01020304050
300
400
500
600
700
800
900
0 1020304050
0
200
400
600
800
10 0 0
12 0 0
14 0 0
16 0 0
0 10 2030 4050
0
200
400
600
800
10 0 0
12 0 0
14 0 0
16 0 0
01020304050
ACS709 Noise versus External Capacitor Value, CF
Capacitor connected between FILTER pin and GND
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristic Performance Data
Data taken using the ACS709-20BB, VCC = 5 V
Accuracy Data
Mean
Typical Maximum Limit Typical Minimum Limit
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
0.20
0.15
0.10
0.05
0
-0.05
-0.10
-0.15
-0.20
-0.25
-0.30
58.0
57.5
57.0
56.5
56.0
55.5
55.0
100.8
100.6
100.4
100.2
100.0
99.8
99.6
99.4
4
3
2
1
0
-1
-2
-3
-4
VOE (mV)ELIN (%)
Sens (mV/A)ESYM (%)
ETOT (%)
T
A
(°C)T
A
(°C)
T
A
(°C)T
A
(°C)
T
A
(°C)
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
Electrical Offset Voltage versus Ambient Temperature
Nonlinearity versus Ambient Temperature
Sensitivity versus Ambient Temperature
Total Output Error versus Ambient Temperature
Symmetry versus Ambient Temperature
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristic Performance Data
Data taken using the ACS709-35BB, VCC = 5 V
Accuracy Data
Mean
Typical Maximum Limit Typical Minimum Limit
20
15
10
5
0
-5
-10
-15
-20
-25
0.30
0.20
0.10
0
-0.10
-0.20
-0.30
29.0
28.8
28.6
28.4
28.2
28.0
27.8
27.6
27.4
101.0
100.8
100.6
100.4
100.2
100.0
99.8
99.6
99.4
99.2
99.0
4
3
2
1
0
-1
-2
-3
-4
VOE (mV)ELIN (%)
Sens (mV/A)ESYM (%)
ETOT (%)
T
A
(°C)T
A
(°C)
T
A
(°C)T
A
(°C)
T
A
(°C)
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
–50 100 125 150500-25 25 75
Electrical Offset Voltage versus Ambient Temperature
Nonlinearity versus Ambient Temperature
Sensitivity versus Ambient Temperature
Total Output Error versus Ambient Temperature
Symmetry versus Ambient Temperature
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
The VOC needed for setting the overcurrent fault
switchpoint can be calculated as follows:
VOC = Sens × | IOC | ,
where VOC is in mV, Sens in mV/A, and IOC (overcur-
rent fault switchpoint) in A.
| Ioc | is the overcurrent fault switchpoint for a bi-
directional (AC) current, which means a bi-directional
device will have two symmetrical overcurrent fault
switchpoints, +IOC and –IOC
.
See the following graph for IOC and VOC ranges.
Setting Overcurrent Fault Switchpoint
IOC
VOC
0.
4 VCC
–
0.25 VCC / Sens
–
0.4 VCC / Sens
0
0.25 VCC / Sens
0.4 VCC / Sens Not in Valid Range
In Valid Range
0.
25
VCC
IOC versus VOC
Example: For ACS709LLFTR-35BB-T, if required overcurrent fault switchpoint is 50 A, and VCC = 5 V, then the
required VOC can be calculated as follows:
VOC = Sens × IOC = 28 × 50 = 1400 (mV)
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Overcurrent Fault Operation
The primary concern with high-speed fault detection is that noise
may cause false tripping. Various applications have or need to
be able to ignore certain faults that are due to switching noise
or other parasitic phenomena, which are application dependant.
The problem with simply trying to filter out this noise up front is
that in high-speed applications, with asymmetric noise, the act of
filtering introduces an error into the measurement. To get around
this issue, and allow the user to prevent the fault signal from
being latched by noise, a circuit was designed to slew the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin voltage based on the value of the capacitor from that pin to
ground. Once the voltage on the pin falls below 2 V, as estab-
lished by an internal reference, the fault output is latched and
pulled to ground quickly with an internal N-channel MOSFET.
Fault Walk-through
The following walk-through references various sections and
attributes in the figure below. This figure shows different
fault set/reset scenarios and how they relate to the voltages on
the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin, FAULT_EN pin, and the internal Overcurrent
(OC) Fault node, which is invisible to the customer.
1. Because the device is enabled (FAULT_EN is high for a mini-
mum period of time, the Fault Enable Delay, tFED
, 15 s typical)
and there is an OC fault condition, the device ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin starts
discharging.
2. When the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin voltage reaches approximately 2 V, the
fault is latched, and an internal NMOS device pulls the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin voltage to approximately 0 V. The rate at which the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin slews downward (see [4] in the figure) is dependent on the
external capacitor, COC, on the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin.
3. When the FAULT_EN pin is brought low, the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin starts
resetting if no OC Fault condition exists. The internal NMOS
pull-down turns off and an internal PMOS pull-up turns on (see
[7] if the OC Fault condition still exists).
4. The slope, and thus the delay, on the fault is controlled by the
capacitor, COC, placed on the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin to ground. During this
portion of the fault (when the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin is between VCC and
2 V), there is a 3 mA constant current sink, which discharges
COC. The length of the fault delay, t, is equal to:
COC ( VCC – 2 V )
3 mA
t= (1)
where VCC is the device power supply voltage.
5. The ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin did not reach the 2 V latch point before the
OC fault condition cleared. Because of this, the fixed 3 mA
current sink turns off, and the internal PMOS pull-up turns on to
recharge COC through the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin.
Functional Description
VCC
2 V
0 V
Time
tFED
FAULT
(Output)
FAULT_EN
(Input)
OC Fault
Condition
(Active High)
2
3
6
6
6
8
1 1 1
4
2
7
4
2
4
4
5
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
13
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6. This curve shows VCC charging external capacitor COC
through the internal PMOS pull-up. The slope is determined
by COC.
7. When the FAULT_EN pin is brought low, if the fault condi-
tion still exists, the latched ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin will stay low until
the fault condition is removed, then it will start resetting.
8. At this point there is a fault condition, and the part is enabled
before the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin can charge to VCC. This shortens the
user-set delay, so the fault is latched earlier. The new delay
time can be calculated by equation 1, after substituting the
voltage seen on the ¯
F
¯
¯
A
¯
¯
U
¯
¯
L
¯
¯
T
¯
pin for VCC.
Chopper Stabilization Technique
Chopper Stabilization is an innovative circuit technique that is
used to minimize the offset voltage of a Hall element and an asso-
ciated on-chip amplifier. Allegro patented a Chopper Stabiliza-
tion 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 tempera-
ture 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.
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.
Amp
Regulator
Clock/Logic
Hall Element
Sample and
Hold
Low-Pass
Filter
Concept of Chopper Stabilization Technique
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
14
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Sensitivity (Sens). The change in device 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 pro-
grammed 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 device 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:
where VIOUT_full-scale amperes = the output voltage (V) when the
sensed current approximates full-scale ±IP .
Symmetry (ESYM). The degree to which the absolute voltage
output from the device varies in proportion to either a positive
or negative full-scale primary current. The following formula is
used to derive symmetry:
Quiescent output voltage (VIOUT(Q)). The output of the device
when the primary current is zero. For a unipolar supply voltage,
it nominally remains at 0.5×VCC. For example, in the case of a
bidirectional output device, 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 out-
put from its ideal quiescent voltage due to nonmagnetic causes. To
convert this voltage to amperes, divide by the device sensitivity,
Sens.
Accuracy (ETOT). The accuracy represents the maximum devia-
tion 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. Note that error is
directly measured during final test at Allegro.
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 full-
scale 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,
VIOUT(Q)RAT (%).
The ratiometric change in sensitivity, SensRAT (%), is defined as:
Definitions of Accuracy Characteristics
100 1–
[{
[{
VIOUT_full-scale amperes – VIOUT(Q)
2 (VIOUT_1/2 full-scale amperes – VIOUT(Q) )
100
VIOUT_+ full-scale amperes – VIOUT(Q)
VIOUT(Q) – VIOUT_–full-scale amperes
100
VIOUT(Q)VCC /VIOUT(Q)5V
VCC /5 V
100
SensVCC /Sens5V
VCC /5 V
Output Voltage versus Sensed Current
Accuracy at 0 A and at Full-Scale Current
Increasing VIOUT
(V)
+IP (A)
Accuracy
Accuracy
Accuracy
25°C Only
Accuracy
25°C Only
Accuracy
25°C Only
Accuracy
0 A
vrOe $Temperature
Average
VIOUT
–IP (A)
vrOe $Temperature
vrOe $Temperature
Decreasing VIOUT
(V)
IP(min)
IP(max)
Full Scale
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
15
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Definitions of Dynamic Response Characteristics
Propagation delay (tPROP). The time required for the device
output to reflect a change in the primary current signal. Propaga-
tion 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.
Primary Current
Transducer Output
90
0
I (%)
Propagation Time, tPROP
t
Primary Current
Transducer Output
90
0
I (%)
Response Time, tRESPONSE
t
Primary Current
Transducer Output
90
10
0
I (%)
Rise Time, tr
t
Rise time (tr). The time interval between a) when the device
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 IC, 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.
Response time (tRESPONSE). The time interval between a) when
the primary current signal reaches 90% of its final value, and b)
when the device reaches 90% of its output corresponding to the
applied current.
High Bandwidth, Fast Fault Response Current Sensor IC
In Thermally Enhanced Package
ACS709
16
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
For the latest version of this document, visit our website:
www.allegromicro.com
Copyright ©2008-2011, Allegro MicroSystems, Inc.
The products described herein are protected by U.S. patents: 7,166,807; 7,425,821; 7,573,393; and 7,598,601.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-
mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;
nor for any in fringe ment of patents or other rights of third parties which may result from its use.
Package LF, 24-pin QSOP
0.635 BSC
0.25
0.15
0.25 MAX
1.75 MAX
8º
0º
1.27
0.41
0.25 BSC
1.04 REF
8.66 ±0.10
3.91 ±0.10
0.30
0.20
5.99 ±0.20
C0.20
24X SEATING
PLANE C
0.635
2.30
5.00
0.40
21
24
GAUGE PLANE
SEATING PLANE
A
C
C
B
A
For Reference Only, not for tooling use (reference JEDEC MO-137 AE)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
B
Reference pad layout (reference IPC7351 SOP63P600X175-24M)
All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances
Terminal #1 mark area
PCB Layout Reference View
Standard Branding Reference View
N = Device part number
T = Temperature code
LF = (Literal) Package type
A = Amperage
TLF-AAA
LLLLLLLLLLL
NNNNNNNNNNNNN
Branded Face
Branding scale and appearance at supplier discretion
