Datasheet A3245 Datasheet (ALLEGRO)

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Package LH, 3-pin Surface Mount

GND

3

1

2

VCC

VOUT

A3245

Chopper-Stabilized

Omnipolar Hall-Effect Switches

The A3245 integrated circuit is an omnipolar, ultrasensitive Hall-effect switch
with a digital output. This sensor has an integrated regulator permitting operation
to 24 V, making it the fi rst omnipolar switch available for operation to 24 V. This
device is especially suited for operation over extended temperature ranges, up
to +150°C. Superior high-temperature performance is made possible through an
Allegro® patented dynamic offset cancellation, which reduces the residual offset
voltage normally caused by device overmolding, temperature excursions, and
thermal stress.

3

The A3245 Hall-effect switch includes the following on a single silicon chip:
voltage regulator, Hall-voltage generator, small-signal amplifi er, chopper stabiliza-
tion, Schmitt trigger, and a short circuit protected open-drain output. Advanced
BiCMOS wafer fabrication processing is used to take advantage of low-voltage
requirements, component matching, very low input-offset errors, and small com­ponent geometries.

Package UA, 3-pin SIP

1 32

VCC

GND

VOUT

1

2

3

AB SO LUTE MAX I MUM RAT INGS

Supply Voltage, V
Reverse-Supply Voltage, V
Reverse-Supply Current, I
Output Off Voltage, V
Output Current, I

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

Operating Temperature
Ambient, T
Ambient, T
Maximum Junction, T
Storage Temperature, T

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

CC

OUT

OUTSINK

, Range E..................–40ºC to 85ºC

A

, Range L................–40ºC to 150ºC

A

........................–18 V

RCC

........................–2 mA

RCC

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

........... Internally Limited

......................165ºC

J(MAX)

.................. –65ºC to 170ºC

S

The omnipolar operation of the A3245 allows activation with either a north or

a south polarity fi eld of suffi cient strength. In the absence of a magnetic fi eld,
the output is off. This patented magnetic-polarity-independence feature makes
this device an excellent replacement for reed switches, with improved ease of
manufacturing, because the A3245 does not require manufacturers to orient their
magnets. These devices allow simple on/off switching in industrial, consumer, and
automotive applications.

The A3245 is rated for operation between the ambient temperatures –40°C and
85°C for the E temperature range, and –40°C to 150°C for the L temperature
range. The small geometries of the BiCMOS process allow these devices to be
provided in ultrasmall packages. The package styles available provide magneti­cally optimized solutions for most applications. Package LH is an SOT23W, a
miniature low-profi le surface-mount package, while package UA is a three-lead
ultramini SIP for through-hole mounting. Each package is available in a lead (Pb)
free version, with 100% matte tin plated leadframes.

Features and Benefi ts

Omnipolar operation

Chopper stabilization

 Superior temperature stability

 Extremely low switchpoint drift

 Insensitive to physical stress

Reverse battery protection

Output short circuit protection

Solid state reliability

Small size

Robust EMC capability

High ESD ratings (HBM)

A3245-DS, Rev. 1

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Product Selection Guide

Part Number Pb-Free Packing* Mounting

A3245ELHLT –

A3245ELHLT-T Yes

A3245EUA –

A3245EUA-T Yes

A3245LLHLT –

A3245LLHLT-T Yes

A3245LUA –

A3245LUA-T Yes

7-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount

Bulk, 500 pieces/bag 3-pin SIP through hole

7-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount

Bulk, 500 pieces/bag 3-pin SIP through hole

*Contact Allegro for additional packing options.

Functional Block Diagram

VCC

Regulator

To All Subcircuits

Ambient, T

(°C)

–40 to 85

–40 to 150

VOUT

A

A3245-DS, Rev. 1

Amp

Cancellation

Dynamic Offset

Amp

Sample and Hold

Filter

Low-Pass

Control

Current Limit

Terminal List

Name Description

VCC Connects power supply to chip 1 1

VOUT Output from circuit 2 3

GND Ground 3 2

Package LH Package UA

<1Ω

GND

Number

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

2

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

OPERATING CHARACTERISTICS valid over full operating voltage and ambient temperature ranges, unless otherwise noted

Characteristic Symbol Test Conditions Min. Typ. Max. Units

Electrical Characteristics

Supply Voltage

Output Leakage Current I

Output On Voltage V

Output Current Limit I

Power-On Time t

Chopping Frequency f

Output Rise Time

Output Fall Time

Supply Current

Reverse Battery Current I

Supply Zener Clamp Voltage V

Supply Zener Current

Magnetic Characteristics

Operate Point

Release Point

Hysteresis

1

Maximum voltage must be adjusted for power dissipation and junction temperature, see Power Derating section.

2

CS = oscilloscope probe capacitance.

3

Maximum current limit is equal to the maximum I

4

Magnetic fl ux density, B, is indicated as a negative value for north-polarity magnetic fi elds, and as a positive value for south-polarity magnetic fi elds.
This so-called algebraic convention supports arithmetic comparison of north and south polarity values, where the relative strength of the fi eld is indicated
by the absolute value of B, and the sign indicates the polarity of the fi eld (for example, a –100 G fi eld and a 100 G fi eld have equivalent strength, but
opposite polarity).

1

2

2

3

4

V

CC

OUTOFF

OUT(SAT)IOUT

OM

PO

c

t

r

t

f

I

CCON

I

CCOFF

RCC

ZSupply

I

ZSupply

B

OPS

B

OPN

B

RPS

B

RPN

B

HYS

Operating, TJ < 165°C 3.6 – 24 V

V

OUT

B > B

VCC > V

R

LOAD

R

LOAD

B > B

B < B

V

RCC

ICC = 6.5 mA; TA = 25°C 28 – – V

VS = 28 V – – 6.5 mA

South pole adjacent to branded face of device 15 38 55 G

North pole adjacent to branded face of device –55 –38 –15 G

South pole adjacent to branded face of device 5 20 50 G

North pole adjacent to branded face of device –50 –20 –5 G

|B

CC(MAX)

= 24 V, B < B

= 20 mA, B > B

OP

CC(MIN)

RP

OP

––10μA

– – 500 mV

30 – 60 mA

––50μs

– 200 – kHz

= 820 Ω, CS = 20 pF – – 1 μs

= 820 Ω, CS = 20 pF – – 1 μs

OP

RP

– 1.5 3.5 mA

– 1.5 3.5 mA

= –18 V – – –2 mA

– B

OPX

+ 3 mA.

RPX

|

51830G

A3245-DS, Rev. 1

DEVICE QUALIFICATION PROGRAM

Contact Allegro for information.

EMC (Electromagnetic Compatibility) REQUIREMENTS

Contact Allegro for information.

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

3

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Electrical Characteristic Data

Supply Current (On) versus Ambient Temperature

5.0

4.0

3.0

(mA)

2.0

CCON

I

1.0

0

–50 0 50 100 150

TA (°C)

Supply Current (Off) versus Ambient Temperature

5.0

4.0

3.0

(mA)

2.0

CCOFF

I

VCC (V)

VCC (V)

Supply Current (On) versus Supply Voltage

5.0

4.0

24

3.6

3.0

(mA)

2.0

CCON

I

1.0

0

0 5 10 15 20 25

VCC (V)

Supply Current (Off) versus Supply Voltage

5.0

4.0

3.0

24

3.6

(mA)

2.0

CCOFF

I

TA (°C)

–40

25

150

TA (°C)

–40

25

150

1.0

0

–50 0 50 100 150

TA (°C)

Output Voltage (On) versus Ambient Temperature

500

450

400

350

300

(mV)

250

200

OUT(SAT)

150

V

100

50

0

–50 0 50 100 150

TA (°C)

VCC (V)

24

3.6

1.0

0

0 5 10 15 20 25

VCC (V)

Output Voltage (On) versus Supply Voltage

500

450

400

350

300

(mV)

250

200

OUT(SAT)

150

V

100

50

0

0 5 10 15 20 25

VCC (V)

TA (°C)

–40

25

150

A3245-DS, Rev. 1

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

4

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Magnetic Characteristic Data

Operate Point (South) versus Ambient Temperature

55

50

45

40

35

(G)

OPS

30

B

25

20

15

–50 0 50 100 150

TA (°C)

Release Point (South) versus Ambient Temperature

50

45

40

35

30

(G)

25

RPS

B

20

15

10

5

–50 0 50 100 150

TA (°C)

TA (°C)

VCC (V)

24

3.6

V

(V)

CC

24

3.6

Operate Point (North) versus Ambient Temperature

-15

-20

-25

-30

-35

(G)

OPN

-40

B

-45

-50

-55

–50 0 50 100 150

TA (°C)

Release Point (North) versus Ambient Temperature

-5

-10

-15

-20

-25

(G)

-30

RPN

B

-35

-40

-45

-50

–50 0 50 100 150

TA (°C)

TA (°C)

VCC (V)

24

3.6

V

(V)

CC

24

3.6

Continued on the next page...

A3245-DS, Rev. 1

Hysteresis versus Ambient Temperature

30

25

20

(G)

HYS

15

B

10

5

–50 0 50 100 150

TA (°C)

VCC (V)

24

3.6

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

5

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Magnetic Characteristic Data (Continued)

Operate Point (South) versus Supply Voltage

55

50

45

40

35

(G)

OPS

30

B

25

20

15

VCC (V)

Release Point (South) versus Supply Voltage

50

45

40

35

30

(G)

25

RPS

B

20

15

10

5

V

(V)

CC

TA (°C)

–40

150

TA (°C)

–40

150

Operate Point (North) versus Supply Voltage

-15

-20

-25

-30

-35

25

(G)

OPN

B

-40

-45

-50

-55

0 5 10 15 25200 5 10 15 2520

VCC (V)

TA (°C)

–40

25

150

Release Point (North) versus Supply Voltage

-5

-10

-15

-20

-25

(G)

25

RPN

B

-30

-35

-40

-45

-50

0 5 10 15 25200 5 10 15 2520

(V)

V

CC

TA (°C)

–40

25

150

A3245-DS, Rev. 1

Hysteresis versus Supply Voltage

30

25

20

(G)

HYS

15

B

10

5

0 5 10 15 2520

VCC (V)

TA (°C)

–40

25

150

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

6

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

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

Characteristic Symbol Test Conditions Value Units

Package Thermal Resistance

Package LH-3, 1-layer PCB with copper limited to
solder pads

R

θJA

Package LH-3, 2-layer PCB with 0.926 in
side, connected by thermal vias

2

on each

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

Power Derating Curve

110 ºC/W

228 ºC/W

165 ºC/W

25
24
23
22
21
20

(V)

19

CC

18
17
16
15
14
13
12
11
10

9
8
7

Maximum Allowable V

6
5
4
3
2

1-layer PCB, Package LH

= 110 °C/W)

(R

θJA

1-layer PCB, Package UA

= 165 °C/W)

(R

θJA

2-layer PCB, Package LH

= 228 °C/W)

(R

θJA

20 40 60 80 100 120 140 160 180

Temperature (°C)

Power Dissipation versus Ambient Temperature

1900
1800
1700
1600
1500
1400
1300

(mW)

D

1200
1100
1000

900
800
700
600
500

Power Dissipation, P

400
300
200
100

0

20 40 60 80 100 120 140 160 180

1-layer PCB, Package LH

(R

θJA

= 110 ºC/W)

1-layer PCB, Packa

(R

θ

JA

=165

º

C

/W)

2-

l

ayer PCB, Package LH

(

R

θJA

=228

ºC/

ge UA

W

)

Temperature (°C)

V

CC( max )

V

CC( min )

A3245-DS, Rev. 1

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

7

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Functional Description

Operation

The output of this device switches low (turns on) when a mag­netic fi eld perpendicular to the Hall sensor exceeds the operate
point, B
voltage is V

(or is less than B

OPS

OUT(SAT)

). After turn-on, the output

OPN

. The output transistor is capable of sink­ing current up to the short circuit current limit, IOM, which is a
minimum of 30 mA. When the magnetic fi eld is reduced below
the release point, B

(or increased above B

RPS

), the device

RPN

output switches high (turns off). The difference in the magnetic
operate and release points is the hysteresis, B

, of the device.

HYS

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

Powering-on the device in a hysteresis region, between B
and B
is attained after the fi rst excursion beyond B

, allows an indeterminate output state. The correct state

RPX

OPX

or B

RPX

OPX

.

Applications

It is strongly recommended that an external bypass capacitor be
connected (in close proximity to the Hall sensor) between the

(A)

V+

OUT

V

Switch to Low

Switch to High

0

B–

B

OPN

RPN

B

B

HYS

Switch to High

0

RPS

B

Switch to Low

B

OPS

B

HYS

B+

V

S

V

OUT(SAT)

supply and ground of the device to reduce both external noise
and noise generated by the chopper stabilization technique. As is
shown in Panel B of fi gure 1, a 0.1μF capacitor is typical.

Omnipolar switches allow operation with either a north pole or
south pole magnet orientation, enhancing product manufactur­ability with the device.

Extensive applications information on magnets and Hall-effect
sensors is available in:

• Hall-Effect IC Applications Guide, AN27701,

• Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead
Welding and Lead Forming, AN27703.1

• Soldering Methods for Allegro’s Products – SMT and Through-
Hole, AN26009

All are provided in Allegro Electronic Data Book, AMS-702 and

the Allegro Web site: www.allegromicro.com

(B)

V

S

C

BYP

0.1 μF

A3245

VCC

VOUT

GND

R

LOAD

Sensor Output

Figure 1: Switching Behavior of Omnipolar Switches. In Panel A, on the horizontal axis, the B+ direction indicates increasing south polarity
magnetic fi eld strength, and the B– direction indicates decreasing south polarity fi eld strength (including the case of increasing north
polarity). This behavior can be exhibited when using a circuit such as that shown in panel B.

A3245-DS, Rev. 1

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

8

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Chopper Stabilization Technique

When using Hall-effect technology, a limiting factor for
switchpoint accuracy is the small signal voltage developed
across the Hall element. This voltage is disproportionally small
relative to the offset that can be produced at the output of the
Hall sensor. This makes it diffi cult to process the signal while
maintaining an accurate, reliable output over the specifi ed oper-
ating temperature and voltage ranges.

Chopper stabilization is a unique approach used to minimize
Hall offset on the chip. The patented Allegro technique, namely
Dynamic Quadrature Offset Cancellation, removes key sources
of the output drift induced by thermal and mechanical stresses.
This offset reduction technique is based on a signal modulation­demodulation process. The undesired offset signal is separated
from the magnetic-fi eld-induced signal in the frequency domain,
through modulation. The subsequent demodulation acts as a
modulation process for the offset, causing the magnetic-fi eld-
induced signal to recover its original spectrum at baseband,
while the dc offset becomes a high-frequency signal. The mag­netic-fi eld-induced signal then can pass through a low-pass fi lter,
while the modulated dc offset is suppressed. This confi guration
is illustrated in fi gure 2.

The chopper stabilization technique uses a 200 kHz high-fre­quency clock. For demodulation process, a sample and hold
technique is used, where the sampling is performed at twice the
chopper frequency (400 kHz). This high-frequency operation
allows a greater sampling rate, which results in higher accuracy
and faster signal-processing capability. This approach desensi­tizes the chip to the effects of thermal and mechanical stresses,
and produces devices that have extremely stable quiescent Hall
output voltages and precise recoverability after temperature
cycling. This technique is made possible through the use of a
BiCMOS process, which allows the use of low-offset, low-noise
amplifi ers in combination with high-density logic integration and
sample-and-hold circuits.

The repeatability of magnetic-fi eld-induced switching is affected
slightly by a chopper technique. However, the Allegro high­frequency chopping approach minimizes the affect of jitter and
makes it imperceptible in most applications. Applications that
are more likely to be sensitive to such degradation are those
requiring precise sensing of alternating magnetic fi elds; for
example, speed sensing of ring-magnet targets. For such applica­tions, Allegro recommends its digital sensor families with lower
sensitivity to jitter. For more information on those devices,
contact your Allegro sales representative.

A3245-DS, Rev. 1

Regulator

Clock/Logic

Hall Element

Amp

Figure 2. Chopper Stabilization Circuit (Dynamic Quadrature Offset Cancellation)

Hold

Sample and

Filter

Low-Pass

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

9

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Power Derating

The device must be operated below the maximum junction
temperature of the device, T

. Under certain combinations of

J(max)

peak conditions, reliable operation may require derating sup­plied power or improving the heat dissipation properties of the
application. This section presents a procedure for correlating
factors affecting operating TJ. (Thermal data is also available on
the Allegro MicroSystems Web site.)

The Package Thermal Resistance, R

, is a fi gure of merit sum-

θJA

marizing the ability of the application and the device to dissipate
heat from the junction (die), through all paths to the ambient air.
Its primary component is the Effective Thermal Conductivity,
K, of the printed circuit board, including adjacent devices and
traces. Radiation from the die through the device case, R
relatively small component of R

. Ambient air temperature,

θJA

θJC

, is

TA, and air motion are signifi cant external factors, damped by
overmolding.

The effect of varying power levels (Power Dissipation, P

), can

D

be estimated. The following formulas represent the fundamental
relationships used to estimate TJ, at PD.

PD = VIN × I

ΔT = P

× R

D

IN

(2)

θJA

(1)

Example: Reliability for V

at TA = 150°C, package LH, using a

CC

low-K PCB.

Observe the worst-case ratings for the device, specifi cally:
R

228 °C/W, T

θJA =

I

CC(max) = 5

mA.

Calculate the maximum allowable power level, P

J(max) =

165°C, V

CC(max) =

24 V, and

D(max)

. First,

invert equation 3:

ΔT

max

= T

– TA = 165 °C – 150 °C = 15 °C

J(max)

This provides the allowable increase to TJ resulting from internal
power dissipation. Then, invert equation 2:

P

D(max)

= ΔT

max

÷ R

= 15°C ÷ 228 °C/W = 65.8 mW

θJA

Finally, invert equation 1 with respect to voltage:

V

CC(est)

= P

D(max)

÷ I

= 65.8 mW ÷ 5 mA = 13.2 V

CC(max)

The result indicates that, at TA, the application and device can
dissipate adequate amounts of heat at voltages ≤V

Compare V
able operation between V
R

. If V

θJA

V

is reliable under these conditions.

CC(max)

CC(est)

CC(est)

to V

≥ V

. If V

CC(max)

CC(est)

CC(max)

CC(est)

and V

CC(max)

, then operation between V

≤ V

CC(max)

requires enhanced

.

CC(est)

, then reli-

CC(est)

and

TJ = TA + ΔT (3)

For example, given common conditions such as: T

V

= 12 V, I

CC

PD = VCC × I

ΔT = PD × R

= 1.5 mA, and R

CC

= 12 V × 1.5 mA = 18 mW

CC

= 18 mW × 165 °C/W = 3°C

θJA

θJA

= 165 °C/W, then:

TJ = TA + ΔT = 25°C + 3°C = 28°C

A worst-case estimate, P
able power level (V
at a selected R

A3245-DS, Rev. 1

and TA.

θJA

CC(max)

, represents the maximum allow-

D(max)

, I

), without exceeding T

CC(max)

= 25°C,

A

J(max)

,

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

10

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

Package LH, 3-Pin (SOT-23W)

Package UA, 3-Pin

A3245-DS, Rev. 1

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

11

A3245

Chopper-Stabilized Omnipolar Hall Effect Switches

A3245-DS, Rev. 1

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 permit 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 products are not authorized for use as critical compo­nents in life-support devices or sys tems without express written
approval.

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.

Copyright © 2005 Allegro MicroSystems, Inc.

Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

www.allegromicro.com

12