A3423

Dual Channel Hall Effect Direction Detection Sensor

Features and Benefits

Description

The A3423 is a dual-channel Hall-effect sensor 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 sensors
are highly sensitive, temperature-stable magnetic sensors ideal
for use in harsh automotive and industrial environments.

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

Packages
8-pin SOIC (suffix L)

4-pin SIP (suffix K)

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 sensor and low noise.
The A3423 has integrated protection against transients on
the supply and output pins and short-circuit protection on all
outputs.

Not to scale

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.

Functional Block Diagram

L package only

VCC

Regulator

Output
Current
Limit

OUTA

Output
Current
Limit

DIR

Output
Current
Limit

SPD

Output
Current
Limit

OUTB

Power-on
Logic

Direction
Logic

E1

Trim

E2

GND

A3423-DS, Rev. 3

L package only

A3423

Dual Channel Hall Effect Direction Detection Sensor

Selection Guide
Part Number

Packing1

Package

A3423EK-T

4-pin through hole SIP

Bulk bag, 500 pieces/bag

A3423ELTR-T

8-pin surface mount SOIC2

Tape and reel, 3000 pieces/reel

A3423LK-T

4-pin through hole SIP

Bulk bag, 500 pieces/bag

A3423LLTR-T
8-pin surface mount SOIC2
1Contact Allegro for additional packing options.
2SOIC package currently in development.

Tape and reel, 3000 pieces/reel

TA
(C)
40 to 85
40 to 150

Absolute Maximum Ratings

Characteristic

Symbol

Notes

Units

Supply Voltage

VCC

30

Reverse Battery Voltage

VRB

30

VOUT

VCC

IOUT(SINK)

30

mA

Output Off Voltage

Output Sink Current
Magnetic Flux Density

40C to 150C

Rating

Unlimited

Range E

40 to 85

Range L

Operating Ambient Temperature

TA

40 to 150

Storage Temperature

Tstg

65 to 165

TJ(max)

165

Maximum Junction Temperature

Pin-out Diagrams

Terminal List Table

Number
K

VCC

8 GND

Name

Description

VCC

Input power supply; tie to GND with bypass capacitor

Output signal indicating direction of target movement

DIR

7 NC

DIR

OUTA

6 NC

OUTA

Analog output indicating B at E1 Hall element

SPD

5 OUTB

SPD

Output signal indicating speed of target movement

OUTB

6, 7

NC

GND

L Package

4
GND

DIR

3
SPD

2
VCC

Analog output indicating B at E2 Hall element

No connection
Ground connection

K Package

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com

A3423

Dual Channel Hall Effect Direction Detection Sensor

OPERATING CHARACTERISTICS valid at TA = 40C to 150C, TJ TJ (max), through full operating air gap range, unless otherwise noted
Characteristics

Symbol

Test Conditions

Min.

Typ.

Max.

Units

3.8

24

<1

10

3.7

Electrical Characteristics
Supply Voltage
Output Leakage Current

VCC

Operating, TJ 165C

IOFF

All outputs VOUT VCC(max)

Undervoltage Lockout

VCC(UV)

Undervoltage Hysteresis

VCC(hys)

Lockout (VCC(UV)) Shutdown

0.4

tr

CLOAD = 20 pF, RLOAD = 1 k

200

ns

tf

CLOAD = 20 pF, RLOAD = 1 k

Output Rise Time

Output Fall Time
Supply Current

ICC

Low Output Voltage

Vsat

Output Current Limit

IOM

Speed Output Delay*

Power-on Time

td
tON

300

ns

3.4

8.2

14

mA

All outputs; IOUT = 15 mA; B > BOP(A), B > BOP(B)

210

500

mV

All outputs

30

60

mA

Delay between direction changing and speed

output transition

0.5

2.5

B > BOP + 5 G

Transient Protection Characteristics

Supply Zener Voltage

VZ(sup)

ICC = 17 mA, TA = 25C

30

Output Zener Voltage

VZ(out)

IOUT = 3 mA, TA = 25C

30

Supply Zener Current

IZ(sup)

Vsupply = 30 V, TA = 25C

17

mA

Output Zener Current

IZ(out)

VOUT = 30 V, TA = 25C

mA

Reverse Battery Current

IRCC

VRCC = 28 V, TA = 25C

15

mA

Operate Point (Channel A and Channel B)

BOP

B(A) > BOP(A), B(B) > BOP(B)

35

15

55

Release Point (Channel A and Channel B)

BRP

B(A) < BOP(A), B(B) < BOP(B)

55

15

35

Bhys

Magnetic Characteristics

Hysteresis (Channel A and Channel B)

BOP BRP

10

30

60

Operate Symmetry

SYMOP(AB)

BOP(A) BOP(B)

50

50

Release Symmetry

SYMRP(AB)

BRP(A) BRP(B)

50

50

* Valid only after the first speed (SPD pin) signal transition. First speed signal transition has no delay.

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com

A3423

Dual Channel Hall Effect Direction Detection Sensor

THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic

Symbol
RJA

Package Thermal Resistance

Test Conditions*

Value Units

Package K, 1-layer PCB with copper limited to solder pads

177

C/W

Package L, 1-layer PCB with copper limited to solder pads

140

C/W

Package L, 4-layer PCB

80

C/W

*Additional thermal information available on Allegro website.

Maximum Allowable VCC (V)

Power Derating Curve

25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2

VCC(max)

Package K
(RQJA = 177 C/W)

1-layer PCB, Package L

(RQJA = 140 C/W)
4-layer PCB, Package L
(RQJA = 80 C/W)
VCC(min)
20

40

60

80

100

120

140

160

180

Temperature (C)

Power Dissipation, PD (mW)

Power Dissipation versus Ambient Temperature

1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0

4
(R -lay
QJ

er
= PC
80 B
C , Pa
/W ck
) ag

1-l
(R ayer
PC
QJ
A =
14 B, P
0 ac
C/ kag
W)
eL

Pac
(R kage K
QJA =
177

20

40

60

C/

W)

80
100
120
Temperature (C)

140

160

180

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com

A3423

Dual Channel Hall Effect Direction Detection Sensor

Performance Characteristics

Supply Current at TA = 25C

Supply Current versus Ambient Temperature

13

10

3 outputs on, Vcc=8V

3 outputs off, Vcc=8V
3 outputs on, Vcc=12V

3 outputs off, Vcc=12V

Supply Current (mA)

Supply Current (mA)

12

11
3 outputs on
3 outputs off

10
9
8
7
6

-50

-25

25

50

75

100

125

150

TA (C)

14

16

18

20

22

24

Magnetic Operate Point versus Ambient Temperature

400

55

350

45

300

35
25

250
200
Iout = 20mA
Iout = 15mA

150

BOP (G)

Vsat (mV)

12

VCC (V)

Saturation Voltage versus Ambient Temperature

100

Vcc = 3.8V
Vcc = 8V
Vcc = 12V
Vcc = 18V
Vcc = 24V

15
5
-5
-15

50

-25

-35

-50

50

100

150

-50

TA (C)

50

100

150

TA (C)

Magnetic Release Point versus Ambient Temperature

Hysteresis versus Ambient Temperature

35

60

25

55
50

15
Vcc = 3.8V
Vcc = 8V
Vcc = 12V
Vcc = 18V
Vcc = 24V

-5
-15
-25
-35

45
Hysteresis (G)

5
BRP (G)

10

Vcc = 3.8V
Vcc = 8V
Vcc = 12V
Vcc = 18V
Vcc = 24V

40
35
30
25
20

-45

15

-55

10

-50

50
TA (C)

100

150

-50

50

100

150

TA (C)

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com

A3423

Dual Channel Hall Effect Direction Detection Sensor

Functional Description

The integrated circuit contains an internal voltage regulator that

powers the Hall sensors and both the analog and digital circuitry.
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.

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 elements.

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 maintained between the target magnetic pole width, the pitch between
the two Hall elements (E1 and E2) in the sensor, and, to a lesser
extent, the magnetic switchpoints.

direction (DIR pin), E1 sensor output (OUTA pin), E2 sensor

output (OUTB pin), and target speed (SPD pin).

For optimal design, the sensor should be actuated by a ring

magnet that presents to the front of the sensor 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 )
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 polepair spacing equal to 6.52 mm (n = 1), 2.17 mm (n = 3), 1.3 mm
(n = 5), and so forth, are permitted.

Outputs The device provides up to four saturated outputs: target

DIR provides the direction output of the sensor 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 internal 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).

Target changes direction of rotation

+B
0
B
+B
0
B

OUTA

OUTB
SPD
(OUTA XOR
OUTB)
DIR

td

Figure 1

Figure 2

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com

A3423

Dual Channel Hall Effect Direction Detection Sensor

Application Information

Operation with Fine-Pitch Ring Magnets. For targets with a

circular pitch of less than 4 mm, a performance improvement can

be observed by rotating the front face of the sensor subassembly
(see below). This sensor 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

Hall sensor) between the supply and ground of the device to

Normal Coplanar Alignment

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 sensors 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.

Rotated Alignment
D cos A

D
Target Profile of Rotation

E1
E1

E2

E2
A

Target Circular Pitch, P

Target Face Width, F

F < D sin A

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com

A3423

Dual Channel Hall Effect Direction Detection Sensor

Package K, 4-Pin SIP

.205 [5.21]

45
B .0704 1.79

B .0642 1.63

.061 [1.55]
.0520 [1.32] B
.135 [3.43]
E1

E2

.033 [0.84]

.085 [2.16]
MAX

.580 [14.73]

45

.016 [0.41]

.017 [0.43]
All dimensions nominal, not for tooling use
Dimensions in inches, metric dimensions (mm) in brackets, for reference only
.050 [1.27]

A Active Area Depth, .0165 [0.42] metric dimensions controlling

B Hall elements (E1 and E2); not to scale

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com

A3423

Dual Channel Hall Effect Direction Detection Sensor

Package L, 8-Pin SOIC

4.90

1.63 .0643

D 1.63 .0642

1.90

0.21

1.95 .0769
D

3.90

4.70
A

E1

1
0.65

E2

0.84

D 1.09 .0429

1.27

0.25

8X
B

6.00

PCB Layout Reference View

SEATING
PLANE

0.10 C

SEATING PLANE
GAUGE PLANE

1.75 MAX

0.41
1.27

0.18

All dimensions nominal, not for tooling use

(reference JEDEC MS-012 AA)
Dimensions in millimeters
A

Terminal #1 mark area

Reference pad layout (reference IPC SOIC127P600-8M)

All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances

Active Area Depth 0.40 mm

Hall elements, E1 and E2 (not to scale); U.S. Customary

dimensions (inches) controlling; shown in brackets

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 departures from the detail specifications as may be required to permit
improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegros 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 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.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com