NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan
for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The
information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no respon-
sibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
Recommended Substitutions:
Dual Channel Hall Effect Direction Detection Sensor IC
A3423
For existing customer transition, and for new customers or new appli-
cations, refer to the A1230.
Date of status change: August 16, 2010
These parts are in production but have been determined to be
NOT FOR NEW DESIGN. This classification indicates that sale of
this device is currently restricted to existing customer applications.
The device should not be purchased for new design applications
because obsolescence in the near future is probable. Samples are no
longer available.
Not for New Design
Description
The A3423 is a dual-channel Hall-effect sensor IC ideal for
use in speed and direction sensing applications incorporating
encoder ring-magnet targets. The A3423 provides various output
signals that indicate speed and direction of target rotation. The
Hall elements are both photolithographically aligned to better
than 1 m. Maintaining accurate displacement between the two
active Hall elements eliminates the major manufacturing hurdle
encountered in fine-pitch detection applications. The A3423 is
a highly sensitive, temperature-stable magnetic device ideal for
use in harsh automotive and industrial environments.
The Hall elements of the A3423 are spaced 1.63 mm apart,
which provides excellent speed and direction information
for small-geometry targets. Extremely low-drift amplifiers
guarantee symmetry between the switches to maintain signal
quadrature. An on-chip regulator allows the use of this device
over a wide operating voltage range of 3.8 to 24 V.
End-of-line trimming of the Hall element switchpoints provides
tight matching capability. The continuous-time nature of the
Hall elements delivers a fast start-up of the device and low
noise.
The A3423 has integrated protection against transients on
the supply and output pins and short-circuit protection on all
outputs.
The A3423 is available in a 4-pin SIP and a plastic 8-pin
SOIC surface mount package (the SOIC version is currently
in development). Both packages are lead (Pb) free, with 100%
matte tin leadframe plating.
A3423-DS, Rev. 5
Features and Benefits
Precisely aligned dual Hall elements
Tightly matched magnetic switchpoints
Speed and direction outputs
Individual Hall element outputs (L package)
Fast power-on time
Output short circuit protection
Operation from an unregulated power supply
Wide operating temperature range
Wide operating voltage range
Integrated EMC-ESD protection
Functional Block Diagram
Not to scale
A3423
Packages
8-pin SOIC (suffix L) 4-pin SIP (suffix K)
Dual Channel Hall Ef fect Direction Detection Sensor IC
Trim
Output
Current
Limit
Output
Current
Limit
Output
Current
Limit
Direction
Logic
Output
Current
Limit
Regulator Power-on
Logic
E1
GND
VCC
E2
L package only
L package only
OUTA
OUTB
SPD
DIR
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
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 Package Packing1TA
(°C)
A3423EK-T 4-pin through hole SIP Bulk bag, 500 pieces/bag –40 to 85
A3423ELTR-T 8-pin surface mount SOIC2Tape and reel, 3000 pieces/reel
A3423LK-T 4-pin through hole SIP Bulk bag, 500 pieces/bag –40 to 150
A3423LLTR-T 8-pin surface mount SOIC2Tape and reel, 3000 pieces/reel
1Contact Allegro for additional packing options.
2SOIC package currently in development.
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Units
Supply Voltage VCC –40°C to 150°C 30 V
Reverse Battery Voltage VRB –30 V
Output Off Voltage VOUT VCC V
Output Sink Current IOUT(SINK) 30 mA
Magnetic Flux Density B Unlimited G
Operating Ambient Temperature TA
Range E –40 to 85 ºC
Range L –40 to 150 ºC
Storage Temperature Tstg –65 to 165 ºC
Maximum Junction Temperature TJ(max) 165 ºC
Terminal List Table
Number Name Description
KL
1 1 VCC Input power supply; tie to GND with bypass capacitor
2 2 DIR Output signal indicating direction of target movement
– 3 OUTA Analog output indicating B at E1 Hall element
3 4 SPD Output signal indicating speed of target movement
– 5 OUTB Analog output indicating B at E2 Hall element
– 6, 7 NC No connection
4 8 GND Ground connection
Pin-out Diagrams
L Package K Package
8
7
6
5
1
2
3
4
GND
NC
NC
OUTB
VCC
DIR
OUTA
SPD
2341
VCC
DIR
SPD
GND
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OPERATING CHARACTERISTICS valid at TA = –40°C to 150°C, TJ ≤ TJ (max), through full operating air gap range, unless otherwise noted
Characteristics Symbol Test Conditions Min. Typ. Max. Units
Electrical Characteristics
Supply Voltage VCC Operating, TJ ≤ 165°C 3.8 – 24 V
Output Leakage Current IOFF All outputs VOUT ≤ VCC(max) – <1 10 μA
Undervoltage Lockout VCC(UV) – – 3.7 V
Undervoltage Hysteresis VCC(hys) Lockout (VCC(UV)) – Shutdown – 0.4 – V
Output Rise Time trCLOAD = 20 pF, RLOAD = 1 kΩ– 200 – ns
Output Fall Time tfCLOAD = 20 pF, RLOAD = 1 kΩ– 300 – ns
Supply Current ICC 3.4 8.2 14 mA
Low Output Voltage Vsat All outputs; IOUT = 15 mA; B > BOP(A), B > BOP(B) – 210 500 mV
Output Current Limit IOM All outputs 30 – 60 mA
Speed Output Delay* td
Delay between direction changing and speed
output transition 0.5 2.5 5 μs
Power-on Time tON B > BOP + 5 G – 2 5 μs
Transient Protection Characteristics
Supply Zener Voltage VZ(sup) ICC = 17 mA, TA = 25°C 30 – – V
Output Zener Voltage VZ(out) IOUT = 3 mA, TA = 25°C 30 – – V
Supply Zener Current IZ(sup) Vsupply = 30 V, TA = 25°C – – 17 mA
Output Zener Current IZ(out) VOUT = 30 V, TA = 25°C – – 3 mA
Reverse Battery Current IRCC VRCC = –28 V, TA = 25°C – – 15 mA
Magnetic Characteristics
Operate Point (Channel A and Channel B) BOP B(A) > BOP(A), B(B) > BOP(B) –35 15 55 G
Release Point (Channel A and Channel B) BRP B(A) < BOP(A), B(B) < BOP(B) –55 –15 35 G
Hysteresis (Channel A and Channel B) Bhys BOP – BRP 10 30 60 G
Operate Symmetry SYMOP(AB) BOP(A) – BOP(B) –50 – 50 G
Release Symmetry SYMRP(AB) BRP(A) – BRP(B) –50 – 50 G
* Valid only after the first speed (SPD pin) signal transition. First speed signal transition has no delay.
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic Symbol Test Conditions* Value Units
Package Thermal Resistance RJA
Package K, 1-layer PCB with copper limited to solder pads 177 ºC/W
Package L, 1-layer PCB with copper limited to solder pads 140 ºC/W
Package L, 4-layer PCB 80 ºC/W
*Additional thermal information available on Allegro website.
6
7
8
9
2
3
4
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
20 40 60 80 100 120 140 160 180
Temperature (ºC)
Maximum Allowable V
CC
(V)
Power Derating Curve
(R
QJA
= 80 ºC/W)
4-layer PCB, Package L
(R
QJA
= 177 ºC/W)
Package K
(R
QJA
= 140 ºC/W)
1-layer PCB, Package L
VCC(min)
VCC(max)
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
20 40 60 80 100 120 140 160 180
Temperature (°C)
Power Dissipation, P
D
(mW)
Power Dissipation versus Ambient Temperature
(R
QJA
= 140 ºC/W)
1-layer PCB, Package L
(RQJA = 177 ºC/W)
Package K
(RQJA = 80 ºC/W)
4-layer PCB, Package L
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Performance Characteristics
Supply Current versus Ambient Temperature
5
6
7
8
9
10
-50 -25 0 25 50 75 100 125 150
T
A
(°C)
Supply Current (mA)
3 outputs on, Vcc=8V
3 outputs off, Vcc=8V
3 outputs on, Vcc=12V
3 outputs off, Vcc=12V
Supply Current at T
A
= 25°C
5
6
7
8
9
10
11
12
13
2 4 6 8 10 12 14 16 18 20 22 24
V
CC
(V)
Supply Current (m A)
3 outputs on
3 outputs off
Saturation Voltage versus Ambient Temperature
0
50
100
150
200
250
300
350
400
-50 0 50 100 150
T
A
(°C)
V
sat
(mV)
Iout = 20mA
Iout = 15mA
Magnetic Operate Point
versus Ambient Temperature
-35
-25
-15
-5
5
15
25
35
45
55
-50 0 50 100 150
TA (°C)
B
OP
(G)
Vcc = 3.8V
Vcc = 8V
Vcc = 12V
Vcc = 18V
Vcc = 24V
Magnetic Release Point versus Ambient Temperature
-55
-45
-35
-25
-15
-5
5
15
25
35
-50 0 50 100 150
TA (°C)
B
RP
(G)
Vcc = 3.8V
Vcc = 8V
Vcc = 12V
Vcc = 18V
Vcc = 24V
Hysteresis versus Ambient Temperature
10
15
20
25
30
35
40
45
50
55
60
-50 0 50 100 150
T
A
(°C)
Hysteresis (G)
Vcc = 3.8V
Vcc = 8V
Vcc = 12V
Vcc = 18V
Vcc = 24V
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
The integrated circuit contains an internal voltage regulator that
powers the Hall elements and both the analog and digital cir-
cuitry. This regulator allows operation over a wide supply voltage
range and provides some immunity to supply noise. The device
also contains logic circuitry that decodes the direction of rotation
of the ring magnet.
Quadrature/Direction Detection Internal logic circuitry provides
outputs representing the speed and direction of the magnetic
field across the face of the package. For the direction signal to be
appropriately updated, a quadrature relationship must be main-
tained between the target magnetic pole width, the pitch between
the two Hall elements (E1 and E2) in the device, and, to a lesser
extent, the magnetic switchpoints.
For optimal design, the device should be actuated by a ring
magnet that presents to the front of the device a field with a pole
width two times the Hall element-to-element spacing. This will
produce a sinusoidal magnetic field whose period (denoted as Τ)
is then four times the element-to-element spacing. A quadrature
relationship can also be maintained for a ring magnet with fields
having a period that satisfies the relationship:
n/4 = 1.63 mm ,
where n is any odd integer. Therefore, ring magnets with pole-
pair spacing equal to 6.52 mm (n = 1), 2.17 mm (n = 3), 1.3 mm
(n = 5), and so forth, are permitted.
The response of the device to the magnetic field produced by a
rotating ring magnet is shown in the Performance Characteristics
section. Note the phase shift between the two integrated Hall ele-
ments.
Outputs The device provides up to four saturated outputs: target
direction (DIR pin), E1 element output (OUTA pin), E2 element
output (OUTB pin), and target speed (SPD pin).
DIR provides the direction output of the device and is defined
as off (high) for targets moving in the direction from E1 to E2
and on (low) for the direction E2 to E1. SPD provides an XORed
output of the two Hall elements (see figure 1). Because of inter-
nal delays, DIR is always updated before SPD and is updated at
every transition of OUTA and OUTB (internal) allowing the use
of up-down counters without the loss of pulses.
Power-on State At power on, the logic circuitry is reset to pro-
vide an off (high) state for all the outputs. If any of the channels
is subjected to a field greater than BOP, the internal logic will set
accordingly, and the outputs will switch to the expected state.
Power-on Time This characteristic, tON, is the elapsed time from
when the supply voltage reaches the device supply minimum
until the device output becomes valid (see figure 2).
Functional Description
Figure 1 Figure 2
+B
0
–B
+B
0
–B
OUTA
OUTB
SPD
DIR
Target changes direction of rotation
td
(OUTA XOR
OUTB)
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Application Information
Operation with Fine-Pitch Ring Magnets. For targets with a cir-
cular pitch of less than 4 mm, a performance improvement can be
observed by rotating the front face of the device (see below). This
rotation decreases the effective Hall element-to-element spacing,
provided that the Hall elements are not rotated beyond the width
of the target.
Applications. It is strongly recommended that an external
0.01 F bypass capacitor be connected (in close proximity to the
device) between the supply and ground of the device to
reduce both external noise and noise generated by the internal
logic.
The simplest form of magnet that will operate these devices is a
ring magnet. Other methods of operation, such as linear magnets,
are possible. Extensive applications information on magnets and
Hall-effect sensor ICs is also available in the “Hall-Effect IC
Applications Guide” which can be found in the latest issue of
Application Note 27701, at www.allegromicro.com/techpub2/an/
an27701.pdf.
E1
E2
E1
D
E2
D cos A
Target Face Width, F
F < D sin A
Target Circular Pitch, P
Normal Coplanar Alignment Rotated Alignment
Target Profile of Rotation
A
NSS
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package K, 4-Pin SIP
2431
E1 E2
1.63 1.79
0.84 REF
1.27 NOM
2.16
MAX
45°
45°
DActive Area Depth, .0.42 mm
Hall elements (E1 and E2); not to scale
D
E
E
E E
B
1.32
Gate and tie bar burr area
A
B
C
Dambar removal protrusion (8X)
A
D
For Reference Only; not for tooling use (reference DWG-9010)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
Standard Branding Reference View
N = Device part number
Y = Last two digits of year of manufacture
W = Week of manufacture
Mold Ejector
Pin Indent
Branded
Face
YYWW
NNNN
1
5.21 +0.08
–0.05
0.38 +0.06
–0.03
3.43 +0.08
–0.05
0.41 +0.07
–0.05
14.73 ±0.51
1.55 ±0.05
Branding scale and appearance at supplier discretion
Dual Channel Hall Ef fect Direction Detection Sensor IC
A3423
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package L, 8-Pin SOIC
For the latest version of this document, visit our website:
www.allegromicro.com
C
SEATING
PLANE
21
8
1.27 BSC
GAUGE PLANE
SEATING PLANE
ATerminal #1 mark area
Active Area Depth 0.40 NOM
B
Reference land pattern layout (reference IPC7351
SOIC127P600X175-8M); all pads a minimum of 0.20 mm from all
adjacent pads; adjust as necessary to meet application process
requirements and PCB layout tolerances
PCB Layout Reference View
B
D
Hall elements (E1 and E2); not to scale
E
C
C
2
E1
E2
1
8
Branding scale and appearance at supplier discretion
C
SEATING
PLANE
0.65 1.27
5.60
1.75
C0.10
8X
0.25 BSC
1.04 REF
1.75 MAX
For Reference Only; not for tooling use (reference MS-012AA)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
4.90 ±0.10
3.90 ±0.10
1.95
1.09
6.00 ±0.20
0.51
0.31 0.25
0.10
0.25
0.17
1.27
0.40
8°
0°
N = Device part number
= Supplier emblem
Y = Last two digits of year of manufacture
W = Week of manufacture
L = Lot number
NNNNNNN
LLLLL
1
YYWW
A
Standard Branding Reference View
D
E
1.63 E
1.63 E
E
Branded Face
Copyright ©2007-2008, Allegro MicroSystems, Inc.
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 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.
