This Hall-effect switch is a monolithic integrated circuit designed to

operate continuously over extended temperatures to +85

C. The unipo-

lar switching characteristic makes this device ideal for use with a simple
bar or rod magnet. The A3161ELT and A3161EUA are identical except
for package.

Each device includes a voltage regulator for operation with supply

voltages of 3.5 to 25 volts, reverse battery protection diode, quadratic
Hall-voltage generator, temperature compensation circuitry, small-signal
amplifier, Schmitt trigger, and a constant-current open-collector output.
Noise radiation is limited by control of the output current slew rate.

Two package styles provide a magnetically optimized package for

most applications. Suffix `LT' is a miniature SOT-89/TO-243AA
transistor package for surface-mount applications; suffix `UA' is a three-
lead ultra-mini SIP for through-hole mounting.

HALL-EFFECT SWITCH

FOR 2-WIRE APPLICATIONS

Always order by complete part number, e.g., A3161ELT .

Data Sheet

27621.30B

Pinning is shown viewed from branded side.

ABSOLUTE MAXIMUM RATINGS

at T

= +25

FEATURES and BENEFITS

Internal Current Regulator for 2-Wire Operation

Output Slew Rate Controlled

3.5 V to 25 V Operation ... Needs Only An Unregulated Supply

Reverse Battery Protection

Excellent Temp. Stability

Activate with Small, Commercially Available Permanent Magnets

Small Size

Solid-State Reliability ... No Moving Parts

Resistant to Physical Stress

3161

Supply Voltage, V

Continuous ................................. 28 V

Surge (t

100 ms) .................... 40 V

Reverse Battery Voltage, V

RCC

Continuous ................................ -25 V

Surge (t

100 ms) ................... -40 V

Magnetic Flux Density, B ....... Unlimited

Output OFF Voltage, V

OUT

.............. 28 V

Operating Temperature Range,

............................. -40

C to +85

Storage Temperature Range,

........................... -65

C to +170

Dwg. PH-003-3

SUPPLY

GROUND

OUTPUT

3161
HALL-EFFECT SWITCH
FOR 2-WIRE APPLICATIONS

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

Limits

At T

= +25

Over Oper. Temp. Range

Characteristic

Symbol

Min.

Typ.

Max.

Min.

Typ.

Max.

Units

Operate Point (output turns OFF)

130

160

130

160

Release Point (output turns ON)

110

Hysteresis (B

- B

)

hys

5.0

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Supply Voltage

Operating

3.5

Load Current

OUT

+ I

3.5 V

OUT

< 12 V, B < B

(2-wire application)

OUT

12 V, B < B

B > B

3.5

5.0

Output Current

OUT

B < B

OFF

OUT

= 24 V, B > B

<1.0

Output Saturation Voltage

OUT

= 5 mA, B < B

0.9

1.5

Output Slew Rate

di/dt

= 20 pF

7.0

mA/

Output Settling Time

= 20 pF

ELECTRICAL CHARACTERISTICS over operating voltage and temperature ranges.

MAGNETIC CHARACTERISTICS over operating supply voltage range.

FUNCTIONAL BLOCK DIAGRAM

NOTE:Typical values are at T

= +25

C and V

= 12 V.

REG.

Dwg. FH-017

GROUND

OUTPUT

3161

HALL-EFFECT SWITCH

FOR 2-WIRE APPLICATIONS

www.allegromicro.com

SWITCH POINTS

TOTAL SUPPLY CURRENT

TYPICAL OPERATING CHARACTERISTICS

OUTPUT SATURATION VOLTAGE

SAFE OPERATING AREA

100

AMBIENT TEMPERATURE in

°
°
°
°

-50

Dwg. GH-044-1

SWITCH POINT in GAUSS

150

200

100

150

-25

125

OVER OPER. VOLT. RANGE

OPERATE POINT

RELEASE POINT

TOTAL SUPPLY CURRENT (I

OUT

+ I

) in mA

100

AMBIENT TEMPERATURE in

°
°
°
°

-50

Dwg. GH-028-4

125

-25

150

5.0

B < B

B > B

= 25 V

= 3.5 V

100

140

AMBIENT TEMPERATURE in

°
°
°
°

MAXIMUM CONTINUOUS SUPPLY VOLTAGE in VOLTS

Dwg. GH-068

120

180

160

PACKAGE SUFFIX

CODE -UA

PACKAGE SUFFIX

CODE -LT

100

1200

AMBIENT TEMPERATURE in

°
°
°
°

800

400

-50

Dwg. GH-029-3

SATURATION VOLTAGE in mV

150

-25

125

OUT

= 5 mA

= 10 V

1000

600

200

3161
HALL-EFFECT SWITCH
FOR 2-WIRE APPLICATIONS

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

Suffix "LT"

SENSOR LOCATIONS

OPERATION

The output of these devices (pin 3) switches OFF when the magnetic

field at the Hall sensor exceeds the operate point threshold (B

). When the

magnetic field is reduced to below the release point threshold (B

), the

device output switches ON. The difference in the magnetic operate and
release points is called the hysteresis (B

hys

) of the device. This built-in

hysteresis allows clean switching of the output even in the presence of
external mechanical vibration and electrical noise.

Suffix "UA"

APPLICATIONS INFORMATION

These devices are normally operated in a 2-wire mode, where the supply

terminal and the output terminal are tied together. An external comparator
detects the change in total supply current by the addition (output off, B > B

)

or subtraction (output on, B < B

) of I

OUT

Hall effect applications information is available in the "Hall-Effect IC

Applications Guide", which can be found in the latest issue of the Allegro
MicroSystems Electronic Data Book, AMS-702 or Application Note 27701,
or at

www.allegromicro.com

TYPICAL 2-WIRE APPLICATION

0.045"
1.14 mm

Dwg. MH-008-7A

0.0305"
0.775 mm
NOM

ACTIVE AREA DEPTH

0.085"

2.16 mm

Dwg. MH-011-8A

0.0195"
0.50 mm
NOM

BRANDED
SURFACE

ACTIVE AREA DEPTH

0.078"

1.98 mm

0.054"

1.36 mm

0.85 V

100

Dwg. EH-011A

0.1

SUPPLY

Icc + Io

100

125

150

175

200

3.0

OUTPUT CURRENT in mA

MAGNETIC FLUX DENSITY in GAUSS

9.0

6.0

Dwg. GH-007-1

= +25

Allegro

3161

HALL-EFFECT SWITCH

FOR 2-WIRE APPLICATIONS

www.allegromicro.com

PACKAGE DESIGNATOR `LT'

(SOT89/TO-243AA)

Dimensions in Inches

(for reference only)

Dimensions in Millimeters

(controlling dimensions)

NOTES: 1.

Exact body and lead configuration at vendor's option within limits shown.

Supplied in bulk pack (500 pieces per bag) or add "TR" to part number for tape and reel.

Only low-temperature (

240

C) reflow-soldering techniques are recommended for SOT89 devices.

Dwg. MA-009-3A in

0.072
0.064

0.167
0.155

0.059

BSC

0.0189
0.0142

0.047
0.035

0.102
0.090

0.063
0.055

0.0173
0.0138

0.090
0.084

0.0221
0.0173

0.118

BSC

0.181
0.173

Dwg. MA-009-3A mm

4.60
4.40

1.83
1.62

4.25
3.94

1.50

BSC

0.48
0.36

1.20
0.89

2.60
2.29

1.60
1.40

0.44
0.35

2.29
2.13

0.56
0.44

3.00

BSC

0.098

0.031

0.102

0.047

0.181

0.079

Dwg. MA-012-3 in

Pads 1, 2, 3, and A -- Standard SOT89 Layout
Pads 1, 2, 3, and B -- Low-Stress Version
Pads 1, 2, and 3 only -- Lowest Stress, But Not Self Aligning

0.028

TYP

0.031

TYP

2.5

0.8

2.6

1.2

4.6

2.0

Dwg. MA-012-3 mm

Pads 1, 2, 3, and A -- Standard SOT89 Layout
Pads 1, 2, 3, and B -- Low-Stress Version
Pads 1, 2, and 3 only -- Lowest Stress, But Not Self Aligning

0.7

TYP

0.8

TYP

3161
HALL-EFFECT SWITCH
FOR 2-WIRE APPLICATIONS

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

Dimensions in Inches

(controlling dimensions)

Dimensions in Millimeters

(for reference only)

PACKAGE DESIGNATOR `UA'

NOTES: 1.

Tolerances on package height and width represent
allowable mold offsets. Dimensions given are
measured at the widest point (parting line).

Exact body and lead configuration at vendor's option
within limits shown.

Height does not include mold gate flash.

Recommended minimum PWB hole diameter to clear
transition area is 0.035" (0.89 mm).

Where no tolerance is specified, dimension is nominal.

Supplied in bulk pack (500 pieces per bag).

Dwg. MH-014E in

0.164
0.159

0.062
0.058

0.0173
0.0138

0.050

BSC

0.640
0.600

0.0189
0.0142

0.085

MAX

0.031

0.122
0.117

SEE NOTE

Dwg. MH-014E mm

4.17
4.04

1.57
1.47

0.44
0.35

1.27

BSC

16.26
15.24

0.48
0.36

2.16

MAX

0.79

3.10
2.97

SEE NOTE

Radial Lead Form (order A3161EUA-LC)

NOTE:

Lead-form dimensions are the nominals produced on the
forming equipment. No dimensional tolerance is implied or
guaranteed for bulk packaging (500 pieces per bag).

0.620"
0.500"

(15.7 mm
12.7 mm)

0.100"

(2.5 mm)

Dwg. MH-026

0.108"

(2.74 mm)

3161

HALL-EFFECT SWITCH

FOR 2-WIRE APPLICATIONS

www.allegromicro.com

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.

Allegro products are not authorized for use as critical components

in life-support appliances, devices, or systems without express written
approval.

The information included herein is believed to be accurate and

reliable. However, Allegro MicroSystems, Inc. assumes no responsibil-
ity for its use; nor for any infringements of patents or other rights of
third parties that may result from its use.

3161
HALL-EFFECT SWITCH
FOR 2-WIRE APPLICATIONS

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

HALL-EFFECT SENSORS

UNIPOLAR HALL-EFFECT DIGITAL SWITCHES

Partial

Operate

Release

Hysteresis

Replaces

Part

Point (G)

(G)

Oper.

and

Number

Over Oper. Voltage & Temp. Range

Temp.

Packages

Comments

A3121x

220 to 500

80 to 410

60 to 150

E, L

LT, UA

3019, 3113, 3119

A3122x

260 to 430

120 to 360

70 to 140

E, L

LT, UA

A3123x

230 to 470

160 to 330

70 to 140

E, L

LT, UA

A3141x

30 to 175

10 to 145

20 to 80

E, L

LT, UA

3040, 3140

A3142x

115 to 245

60 to 190

30 to 80

E, L

LT, UA

A3143x

205 to 355

150 to 300

30 to 80

E, L

LT, UA

A3144x

35 to 450

25 to 430

>20

E, L

LT, UA

3020, 3120

A3161E

<160 (Typ 130)

>30 (Typ 110)

5 to 80

LT, UA

2-wire operation

A3240x

<50 (Typ 35)

>5 (Typ 25)

Typ 10

E, L

LH, LT, UA

chopper stabilized

A3361E

<125

>40

5 to 30

LH, LT, UA

2-wire, chopper stabilized,

output normally high

A3362E

<125

>40

5 to 30

LH, LT, UA

2-wire, chopper stabilized,

output normally low

Notes: 1) Typical data is at TA = +25

C and nominal operating voltage.

2) "x" = Operating Temperature Range [suffix letter or (prefix)]: S (UGN) = -20

C to +85

C, E = -40

C to +85

J = -40

C to +115

C, K (UGS) = -40

C to +125

C, L (UGL) = -40

C to +150

Part Number A3161E