Description
The A1126 integrated circuit is an omnipolar, ultrasensitive
Hall-effect switch with a digital output. This device has an
integrated regulator permitting operation to 24 V.
This device is especially suited for operation through 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.
The A1126 Hall-effect switch includes the following on a
single silicon chip: voltage regulator, Hall-voltage generator,
small-signal amplifier, chopper stabilization, 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.
The omnipolar operation of the A1126 allows activation with
either a north or a south polarity field of sufficient strength.
In the absence of a magnetic field, 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 A1126 does not
A1126-DS
Features and Benefits
• Omnipolar operation
• Low switchpoint drift
• Superior temperature stability
• Insensitive to physical stress
• Reverse battery protection
• Robust EMC capability
• Robust ESD protection
Chopper Stabilized Omnipolar Hall-Ef fect Switch
Functional Block Diagram
Not to scale
A1126
To all subcircuits
GND
VOUT
Omnipolar
Switchpoints
Dynamic Offset Cancellation
Amplifier
Regulator
VCC
Control
Signal
Recovery
Current
Limit
Continued on the next page…
Packages:
Approximate footprint
3-pin SOT23-W
2 mm × 3 mm × 1 mm
(suffix LH)
3-pin ultramini SIP
1.5 mm × 4 mm × 3 mm
(suffix UA)
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Pin-out Diagrams
LH Package
3-pin SOT23W
UA Package
3-pin SIP
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Unit
Forward Supply Voltage VCC 28 V
Reverse Supply Voltage VRCC –18 V
Output Off Voltage VOUT 28 V
Reverse Supply Current IRCC –2 mA
Continuous Output Current IOUT Internally limited –
Operating Ambient Temperature TAL temperature range –40 to 150 ºC
Maximum Junction Temperature TJ(max) 165 ºC
Storage Temperature Tstg –65 to 170 ºC
Terminal List Table
Name Number Function
LH UA
VCC 1 1 Connects power supply to chip
VOUT 2 3 Output from circuit
GND 3 2 Ground
require manufacturers to orient their magnets. These devices allow
simple on/off switching in industrial, consumer, and automotive
applications.
The A1126 is rated for operation between the ambient temperatures
–40°C to 150°C. The available package styles provide magnetically
optimized solutions for most applications. Package LH is an SOT23W,
a miniature low-profile surface-mount package, while package UA is
a three-lead ultramini SIP for through-hole mounting. Each package
is lead (Pb) free, with 100% matte tin plated leadframe.
Description (continued)
Selection Guide
Part Number Packing1Package
A1126LLHLT-T23,000 pieces per reel 3-pin SOT-23W surface mount
A1126LLHLX-T 10,000 pieces per reel 3-pin SOT-23W surface mount
A1126LUA-T 500 pieces per bag 3-pin ultramini SIP through-hole mount
1Contact Allegro® for additional packing options
2Available through authorized Allegro distributors only.
1
3
2
1
2
3
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OPERATING CHARACTERISTICS Valid through TA and VCC ranges, TJ < TJ(max), CBYP = 0.1 μF; unless otherwise specified
Characteristics Symbol Test Conditions Min. Typ. Max. Unit1
Electrical Characteristics
Supply Voltage VCC Operating, TJ < 165°C 3 – 24 V
Output Leakage Current IOUTOFF VOUT = 24 V, B < BRPS ––10μA
Output On Voltage VOUT(SAT) IOUT = 20 mA, B > BOP – 185 500 mV
Output Current Limit IOM B > BOP 30 – 60 mA
Power-On Time2,3 tPO ––25μs
Chopping Frequency fC– 800 – kHz
Output Rise Time3,4 trRLOAD = 820 Ω, CS = 20 pF – 0.2 2 μs
Output Fall Time3,4 tfRLOAD = 820 Ω, CS = 20 pF – 0.1 2 μs
Supply Current ICC(ON) B > BOP
, VCC = 12 V – – 4 mA
ICC(OFF) B < BRP
, VCC = 12 V – – 4 mA
Supply Zener Clamp Voltage VZ I
CC = 6.5 mA; TA = 25°C 28 – – V
Supply Zener Current IZSUPPLY VS = 28 V – – 6.5 mA
Magnetic Characteristics
Operate Point BOPS South pole adjacent to branded face 15 38 55 G
BOPN North pole adjacent to branded face -55 -38 -15 G
Release Point BRPS South pole adjacent to branded face 5 20 50 G
BRPN North pole adjacent to branded face -50 -20 -5 G
Hysteresis BHYS | BOPS – BRPS
|, | BOPN – BRPN |5–30G
11 G (gauss) = 0.1 mT (millitesla).
2B < BRP
(min) – 10 G , B > BOP
(max) + 10 G.
3Guaranteed by device design and characterization.
4CS = oscilloscope probe capacitance.
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristic Performance
Supply Current, ICC(OFF) (mA)
Supply Voltage, VCC (V)
TA = 150°C
TA = –40°C
TA = 25°C
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
Average Supply Current (Off) versus Supply Voltage
0 5 10 15 20 25
Ambient Temperature, TA (°C)
Supply Current, ICC(OFF) (mA)
-60 -40 -20 0 20 40 60 80 100 140120 160
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
Ambient Temperature, TA (°C)
-60 -40 -20 0 20 40 60 80 100 140120 160
VCC = 3.0 V
VCC = 24 V
Average Supply Current (Off) versus Temperature
TA = 150°C
TA = –40°C
TA = 25°C
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0 5 10 15 20 25
Supply Voltage, VCC (V)
Supply Current, ICC(ON) (mA)
Average Supply Current (On) versus Supply Voltage
VCC = 3.0 V
VCC = 24 V
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
-60 -40 -20 0 20 40 60 80 100 140120 160
Ambient Temperature, TA (°C)
Supply Current, ICC(ON) (mA)
Average Supply Current (On) versus Temperature
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Release Point (BRP)
Applied Flux Density (G)
Supply Voltage, VCC (V)
TA = 150°C
TA = –40°C
TA = 25°C
50
45
40
35
30
25
20
15
10
5
Average Release Point (South) versus Supply Voltage
0 5 10 15 20 25
Ambient Temperature, TA (°C)
Release Point (BRP)
Applied Flux Density (G)
-60 -40 -20 0 20 40 60 80 100 140120 160
50
45
40
35
30
25
20
15
10
5
Ambient Temperature, TA (°C)
-60 -40 -20 0 20 40 60 80 100 140120 160
VCC = 3.0 V
VCC = 24 V
Average Release Point (South) versus Temperature
TA = 150°C
TA = –40°C
TA = 25°C
55
50
45
40
35
30
25
20
15
0 5 10 15 20 25
Supply Voltage, VCC (V)
Operate Point (BOP)
Applied Flux Density (G)
Average Operate Point (South) versus Supply Voltage
VCC = 3.0 V
VCC = 24 V
55
50
45
40
35
30
25
20
15
-60 -40 -20 0 20 40 60 80 100 140120 160
Ambient Temperature, TA (°C)
Operate Point (BOP)
Applied Flux Density (G)
Average Operate Point (South) versus Temperature
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Release Point (BRP)
Applied Flux Density (G)
Supply Voltage, VCC (V)
TA = 150°C
TA = –40°C
–5
–10
–15
–20
–25
–30
–35
–40
–45
–50
Average Release Point (North) versus Supply Voltage
0 5 10 15 20 25
TA = 25°C
Ambient Temperature, TA (°C)
Release Point (BRP)
Applied Flux Density (G)
-60 -40 -20 0 20 40 60 80 100 140120 160
–5
–10
–15
–20
–25
–30
–35
–40
–45
–50
Ambient Temperature, TA (°C)
-60 -40 -20 0 20 40 60 80 100 140120 160
VCC = 3.0 V
VCC = 24 V
Average Release Point (North) versus Temperature
TA = 150°C
TA = –40°C
TA = 25°C
–15
–20
–25
–30
–35
–40
–45
–50
–55
0 5 10 15 20 25
Supply Voltage, VCC (V)
Operate Point (BOP)
Applied Flux Density (G)
Average Operate Point (North) versus Supply Voltage
VCC = 3.0 V
VCC = 24 V
–15
–20
–25
–30
–35
–40
–45
–50
–55
-60 -40 -20 0 20 40 60 80 100 140120 160
Ambient Temperature, TA (°C)
Operate Point (BOP)
Applied Flux Density (G)
Average Operate Point (North) versus Temperature
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
-60 -40 -20 0 20 40 60 80 100 140120 160
Ambient Temperature, TA (°C)
Output Saturation Voltage
VOUT(SAT), (mV)
500
450
400
350
300
250
200
150
100
50
0
Average Output Saturation Voltage versus Temperature
IOUT = 20 mA, VCC = 12 V, B > BOP
Switchpoint Hysteresis (BHYS)
Applied Flux Density (G)
Supply Voltage, VCC (V)
TA = 150°C
TA = –40°C
30
25
20
15
10
5
Average Hysteresis (North) versus Supply Voltage
0 5 10 15 20 25
TA = 25°C
Ambient Temperature, TA (°C)
Switchpoint Hysteresis (BHYS)
Applied Flux Density (G)
-60 -40 -20 0 20 40 60 80 100 140120 160
30
25
20
15
10
5
Ambient Temperature, TA (°C)
-60 -40 -20 0 20 40 60 80 100 140120 160
VCC = 3.0 V
Average Hysteresis (North) versus Temperature
VCC = 24 V
TA = 150°C
TA = –40°C TA = 25°C
30
25
20
15
10
5
0 5 10 15 20 25
Supply Voltage, VCC (V)
Switchpoint Hysteresis (BHYS)
Applied Flux Density (G)
Average Hysteresis (South) versus Supply Voltage
VCC = 3.0 V
VCC = 24 V
30
25
20
15
10
5
-60 -40 -20 0 20 40 60 80 100 140120 160
Ambient Temperature, TA (°C)
Switchpoint Hysteresis (BHYS)
Applied Flux Density (G)
Average Hysteresis (South) versus Temperature
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
8
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 RθJA
Package LH, 1-layer PCB with copper limited to solder pads 228 ºC/W
Package LH, 2-layer PCB with 0.463 in.2 of copper area each side
connected by thermal vias 110 ºC/W
Package UA, 1-layer PCB with copper limited to solder pads 165 ºC/W
*Additional thermal information available on Allegro Web site.
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
= 228 ºC/W)
1-layer PCB, Package LH
(R
QJA
= 110 ºC/W)
2-layer PCB, Package LH
(R
QJA
= 165 ºC/W)
1-layer PCB, Package UA
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
θJA
= 165 ºC/W)
1-layer PCB, Package UA
(RθJA = 228 ºC/W)
1-layer PCB, Package LH
(RθJA = 110 ºC/W)
2-layer PCB, Package LH
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Functional Description
The output of these devices switches low (turns on) when a
magnetic field perpendicular to the Hall sensor chip exceeds the
operate point threshold, BOPx . After turn-on, the output voltage
is VOUT(SAT)
. 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 field is reduced below the release
point, BRPx , the device output goes high (turns off). The differ-
ence in the magnetic operate and release points is the hysteresis,
BHYS , of the device. This built-in hysteresis allows clean switch-
ing of the output even in the presence of external mechanical
vibration and electrical noise.
In the case of omnipolar switch devices, removal of the magnetic
field results in the device output high (off).
Powering-on the device in the hysteresis range (less than BOPx
and greater than BRPx
) will allow an indeterminate output state.
The correct state is attained after the first excursion beyond BOPx
or BRPx .
Figure 1. Switching behavior of omnipolar switches. On the horizontal axis, the
B+ direction indicates increasing south polarity magnetic field strength, and the
B– direction indicates increasing north polarity. This behavior can be exhibited
when using a circuit such as that shown in figure 2.
BOPS
BOPN
BRPN
BRPS
BHYS
BHYS
VS
VOUT
VOUT(SAT)
Switch to Low
Switch to Low
Switch to High
Switch to High
B+
B–
V+
00
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Application Information
Figure 2. Typical Application Circuit
Figure 3. Concept of Chopper Stabilization Technique
VCC
V+
GND
VOUT
CBYPASS
0.1 μF
RLOAD
A1126
Amp
Regulator
Clock/Logic
Hall Element
Sample and
Hold
Low-Pass
Filter
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
chip. This makes it difficult to process the signal while main-
taining an accurate, reliable output over the specified operating
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 Cancella-
tion, removes key sources of the output drift induced by thermal
and mechanical stresses. This offset reduction technique is based
on a signal modulation-demodulation process. The undesired
offset signal is separated from the magnetic field-induced signal
in the frequency domain, through modulation. The subsequent
demodulation acts as a modulation process for the offset, causing
the magnetic field-induced signal to recover its original spec-
trum at baseband, while the DC offset becomes a high-frequency
signal. The magnetic-sourced signal then can pass through a
low-pass filter, while the modulated DC offset is suppressed. The
chopper stabilization technique uses a 400 kHz high frequency
clock. For demodulation process, a sample-and-hold technique is
used, where the sampling is performed at twice the chopper fre-
quency. 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 amplifiers in combination with high-
density logic integration and sample-and-hold circuits.
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
The device must be operated below the maximum junction
temperature of the device, TJ(max) . Under certain combina-
tions of 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, RJA, is a figure of merit sum-
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, RJC, is
relatively small component of RJA. Ambient air temperature,
TA, and air motion are significant external factors, damped by
overmolding.
The effect of varying power levels (Power Dissipation, PD), can
be estimated. The following formulas represent the fundamental
relationships used to estimate TJ, at PD.
P
D = VIN × IIN
(1)
T = PD × RJA (2)
T
J = TA + ΔT (3)
For example, given common conditions such as: TA= 25°C,
VIN = 12 V, IIN = 4 mA, and RJA = 140 °C/W, then:
P
D = VIN × IIN = 12 V × 4 mA = 48 mW
T = PD × RJA = 48 mW × 140 °C/W = 7°C
T
J = TA + T = 25°C + 7°C = 32°C
A worst-case estimate, PD(max) , represents the maximum allow-
able power level, without exceeding TJ(max) , at a selected RJA
and TA.
Example: Reliability for VCC at TA =
150°C, package UA, using a
single-layer PCB.
Observe the worst-case ratings for the device, specifically:
RJA
=
165 °C/W, TJ(max)
=
165°C, VCC(max)
=
24
V, and
ICC(max) = 4 mA.
Calculate the maximum allowable power level, PD(max) . First,
invert equation 3:
Tmax = TJ(max) – TA = 165
°C
–
150
°C = 15
°C
This provides the allowable increase to TJ resulting from internal
power dissipation. Then, invert equation 2:
PD(max) = Tmax ÷ RJA = 15°C ÷ 165 °C/W = 91 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 91 mW ÷ 4 mA = 23 V
The result indicates that, at TA, the application and device can
dissipate adequate amounts of heat at voltages ≤VCC(est) .
Compare VCC(est) to VCC(max) . If VCC(est) ≤ VCC(max) , then
reliable operation between VCC(est) and VCC(max) requires
enhanced RJA. If VCC(est) ≥ VCC(max) , then operation
between VCC(est) and VCC(max) is reliable under these condi-
tions.
Power Derating
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package LH, 3-Pin SOT23W
0.55 REF
Gauge Plane
Seating Plane
0.25 BSC
0.95 BSC
0.95
1.00
0.70 2.40
2
1
AActive Area Depth, 0.28 mm REF
B
C
C
B
Reference land pattern layout
All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances
Branding scale and appearance at supplier discretion
A
PCB Layout Reference View
Standard Branding Reference View
1
Branded Face
N = Last three digits of device part number
NNN
2.90 +0.10
–0.20
4°±4°
8X 10° REF
0.180+0.020
–0.053
0.05 +0.10
–0.05
0.25 MIN
1.91 +0.19
–0.06
2.98 +0.12
–0.08
1.00 ±0.13
0.40 ±0.10
For Reference Only; not for tooling use (reference DWG-2840)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
DHall element, not to scale
D
D
D
1.49
0.96
3
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
13
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package UA, 3-Pin SIP
231
0.79 REF
1.27 NOM
2.16
MAX
0.51
REF
45°
C
45°
B
E
E
E
2.04
1.44
Gate burr area
A
B
C
Dambar removal protrusion (6X)
A
D
E
D
Branding scale and appearance at supplier discretion
Hall element, not to scale
Active Area Depth, 0.50 mm REF
For Reference Only; not for tooling use (reference DWG-9049)
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
= Supplier emblem
N = Last three digits of device part number
NNN
1
Mold Ejector
Pin Indent
Branded
Face
4.09 +0.08
–0.05
0.41 +0.03
–0.06
3.02 +0.08
–0.05
0.43 +0.05
–0.07
15.75 ±0.51
1.52 ±0.05
Chopper Stabilized Omnipolar Hall-Ef fect Switch
A1126
14
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Copyright ©2010-2011, Allegro MicroSystems, Inc.
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.
For the latest version of this document, visit our website:
www.allegromicro.com
Revision History
Revision Revision Date Description of Revision
Final September 22, 2011 Final release
