Description
The A1120, A1121, A1122, and A1125 Hall-effect, unipolar
switches are extremely temperature-stable and stress-resistant
sensor ICs, especially suited for operation over extended
temperature ranges to 150°C. Superior high-temperature
performance is made possible through dynamic offset
cancellation, which reduces the residual offset voltage normally
caused by device overmolding, temperature dependencies, and
thermal stress.
Each device includes on a single silicon chip a voltage regulator,
Hall-voltage generator, small-signal amplifier, chopper
stabilization, Schmitt trigger, and a short-circuit protected
open-drain output to sink up to 25 mA.
An on-board regulator permits operation with supply voltages
of 3 to 24 V. The advantage of operating down to 3 V is that
the device can be used in 3 V applications or with additional
external resistance in series with the supply pin for greater
protection against high voltage transient events.
For the A1120, A1121, and A1122, a south pole of sufficient
strength turns the output on. Removal of the magnetic field
turns the output off. The A1125 is complementary, in that for
these devices, a south pole turns the A1125 output off, and
removal of the magnetic field turns the output on.
Two package styles provide a magnetically optimized package
for most applications. Package type LH is a modified SOT23W,
surface mount package, while UA is a three-lead ultra-mini SIP
for through-hole mounting. Each package type is lead (Pb) free
(suffix, –T), with a 100% matte tin plated leadframe.
A1120-DS, Rev. 14
Features and Benefits
▪ Unipolar switchpoints
▪ Resistant to physical stress
▪ Superior temperature stability
▪ Output short-circuit protection
▪ Operation from unregulated supply
▪ Reverse battery protection
▪ Solid-state reliability
▪ Small package sizes
Chopper Stabilized Precision Hall Ef fect Switches
Packages:
Functional Block Diagram
Not to scale
A1 120, A1 121, A1122, and A1 125
3-pin SOT23W (suffix LH)
3-pin SIP (suffix UA)
Regulator
GND
VCC
VOUT
Control
Current Limit
Dynamic Offset
Cancellation
Sample and Hold
To All Subcircuits
Amp
Low-Pass
Filter
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
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 Packing1Mounting Ambient, TA
Switchpoints
(Typ.) Output In South (Positive)
Magnetic Field
BOP BRP
A1120ELHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 85ºC
35 25
On (logic low)
A1120ELHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1120EUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
A1120LLHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 150ºCA1120LLHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1120LUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
A1121ELHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 85ºC
95 70
A1121ELHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1121EUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
A1121LLHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 150ºCA1121LLHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1121LUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
A1122ELHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 85ºC
150 125
A1122ELHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1122EUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
A1122LLHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 150ºCA1122LLHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1122LUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
A1125ELHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 85ºC
35 25 Off (logic high)
A1125ELHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1125EUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
A1125LLHLX-T 13-in. reel, 10000 pieces/reel 3-pin SOT23W surface mount
–40ºC to 150ºCA1125LLHLT-T27-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount
A1125LUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
*Contact Allegro for additional packing options.
2Available through authorized Allegro distributors only.
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Units
Forward Supply Voltage VCC 26.5 V
Reverse Supply Voltage VRCC –30 V
Output Off Voltage VOUT 26 V
Continuous Output Current IOUT 25 mA
Reverse Output Current IROUT –50 mA
Operating Ambient Temperature TA
Range E –40 to 85 ºC
Range L –40 to 150 ºC
Maximum Junction Temperature TJ(max) 165 ºC
Storage Temperature Tstg –65 to 170 ºC
Pin-out Diagrams
Terminal List
Name Description Number
Package LH Package UA
VCC Connects power supply to chip 1 1
VOUT Output from circuit 2 3
GND Ground 3 2
1
3
2
GND
VOUT
VCC
Package UAPackage LH
1
2
3
GND
VOUT
VCC
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ELECTRICAL CHARACTERISTICS Valid valid over full operating voltage and ambient temperature ranges; unless otherwise noted
Characteristics Symbol Test Conditions Min. Typ.1Max. Unit2
Electrical Characteristics
Forward Supply Voltage VCC Operating, TJ < 165°C 3 – 24 V
Output Leakage Current IOUTOFF
A1120,
A1121,
A1122
VOUT = 24 V, B < BRP ––10μA
A1125 VOUT = 24 V, B > BOP ––10μA
Output Saturation Voltage VOUT(SAT)
A1120,
A1121,
A1122
IOUT = 20 mA, B > BOP – 185 500 mV
A1125 IOUT = 20 mA, B < BRP – 185 500 mV
Output Current Limit IOM
A1120,
A1121,
A1122
B > BOP 30 – 60 mA
A1125 B < BRP 30 – 60 mA
Power-On Time3tPO
VCC > 3.0 V, B < BRP(min) – 10 G,
B > BOP(max) + 10 G ––25μs
Chopping Frequency fC– 800 – kHz
Output Rise Time3,4 trRL = 820 Ω, CS = 20 pF – 0.2 2 μs
Output Fall Time3,4 tfRL = 820 Ω, CS = 20 pF – 0.1 2 μs
Supply Current
ICC(ON)
A1120,
A1121,
A1122
VCC = 12 V, B > BOP ––4mA
A1125 VCC = 12 V, B < BRP ––4mA
ICC(OFF)
A1120,
A1121,
A1122
VCC = 12 V, B < BRP ––4mA
A1125 VCC = 12 V, B > BOP ––4mA
Reverse Supply Current IRCC VRCC = –30 V – – –5 mA
Supply Zener Clamp Voltage VZICC = 5 mA; TA = 25°C 28 – – V
Zener Impedance IZICC = 5 mA; TA = 25°C – 50 – Ω
Magnetic Characteristics
Operate Point BOP
A1120 – 35 50 G
A1121 50 95 135 G
A1122 120 150 200 G
A1125 – 35 50 G
Release Point BRP
A1120 5 25 – G
A1121 40 70 110 G
A1122 110 125 190 G
A1125 5 25 – G
Hysteresis BHYS
A1120,
A1125 (BOP – BRP)–10–G
A1121,
A1122 10 25 42 G
1Typical data are are at TA = 25°C and VCC = 12 V, and are for initial design estimations only.
21 G (gauss) = 0.1 mT (millitesla).
3Guaranteed by device design and characterization.
4CS = oscilloscope probe capacitance.
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
5
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
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
Maximum Allowable V
CC
(V)
TJ(max) = 165ºC; ICC = ICC(max)
Power Derating Curve
(R
QJA
= 228 ºC/W)
Package LH, 1-layer PCB
(R
QJA
= 110 ºC/W)
Package LH, 2-layer PCB
(R
QJA
= 165 ºC/W)
Package UA, 1-layer PCB
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, PD (mW)
Power Dissipation versus Ambient Temperature
(R
QJA
= 165 ºC/W)
Package UA, 1-layer PCB
(R
QJA
= 228 ºC/W)
Package LH, 1-layer PCB
(R
QJA
= 110 ºC/W)
Package LH, 2-layer PCB
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristic Performance
A1120, A1121, and A1125 Electrical Characteristics
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
2 6 10 14 18 22 26
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
-60 - 40 - 20 0 20 40 60 80 100 120 140 160
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
-60 - 40 - 20 0 20 40 60 80 100 120 140 160
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
2 6 10 14 18 22 26
0
50
100
150
200
250
300
- - - 0 20 40 60 80 100 120 140 160
0
50
100
150
200
250
300
2 6 10 14 18 22 26
60 40 20
A
verage
S
upp
l
y
C
urren
t
(O
n
)
versus
A
verage
S
upp
l
y
V
o
lt
age
A
verage
S
upp
l
y
C
urren
t
(O
n
)
versus
A
m
bi
en
t
T
empera
t
ure
Average Supply Current (Off) versus Average Supply VoltageAverage Supply Current (Off) versus Ambient Temperature
Average Output Saturation Voltage versus Supply Voltage
Average Output Saturation Voltage versus Ambient Temperature
TA (°C)
ICC(av) (mA)
ICC(av) (mA)
ICC(av) (mA)
ICC(av) (mA)
VOUT(sat) (V)
VOUT(sat) (V)
VCC (V)
TA (°C) VCC (V)
TA (°C) VCC (V)
TA (°C)
–40
25
150
TA (°C)
–40
25
150
TA (°C)
–40
25
150
VCC (V)
3.0
12
24
VCC (V)
3.0
12
24
VCC (V)
3.0
3.8
4.2
12
24
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
A1120 and A1125 Magnetic Characteristics
0
5
10
15
20
25
30
35
40
45
50
-60 -40 -20 0 20 40 60 80 100 120 140 160
0
5
10
15
20
25
30
35
40
45
50
-60 -40 -20 0 20 40 60 80 100 120 140 160
0
2
4
6
8
10
12
14
16
18
20
-60 -40 -20 0 20 40 60 80 100 120 140 160
0
5
10
15
20
25
30
35
40
45
50
2 6 10 14 18 22 26
0
5
10
15
20
25
30
35
40
45
50
2 6 10 14 18 22 26
0
2
4
6
8
10
12
14
16
18
20
2 6 10 14 18 22 26
Average Operate Point versus Average Supply VoltageAverage Operate Point versus Ambient Temperature
Average Release Point versus Average Supply VoltageAverage Release Point versus Ambient Temperature
Average Switchpoint Hysteresis versus Supply Voltage
Average Switchpoint Hysteresis versus Ambient Temperature
TA (°C)
BOP (G)
BOP (G)
BRP (G)
BRP (G)
BHYS (G)
BHYS (G)
VCC (V)
TA (°C) VCC (V)
TA (°C) VCC (V)
VCC (V)
3.0
24
VCC (V)
3.0
24
VCC (V)
3.0
24
TA (°C)
–40
25
150
TA (°C)
–40
25
150
TA (°C)
–40
25
150
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
A1121 Magnetic Characteristics
- 60 - 40 - 20 0 20 40 60 80 100 120 140 160 2 6 10 14 18 22 26
26
- 60 - 40 - 20 0 20 40 60 80 100 120 140 160 2 6 10 14 18 22
- 60 - 40 - 20 0 20 40 60 80 100 120 140 160 2 6 10 14 18 22 26
40
50
60
70
80
90
100
110
10
15
20
25
30
35
40
50
60
70
80
90
100
110
120
130
140
50
60
70
80
90
100
110
120
130
140
40
50
60
70
80
90
100
110
10
15
20
25
30
35
40
Operate Point versus Average Supply VoltageOperate Point versus Ambient Temperature
Release Point versus Average Supply VoltageRelease Point versus Ambient Temperature
Switchpoint Hysteresis versus Supply Voltage
Switchpoint Hysteresis versus Ambient Temperature
TA (°C)
BOP (G)
BOP (G)
BRP (G)
BRP (G)
BHYS (G)
BHYS (G)
VCC (V)
TA (°C) VCC (V)
TA (°C) V
CC
(
V
)
VCC (V)
3.0
12
24
VCC (V)
3.0
12
24
VCC (V)
3.0
12
24
TA (°C)
–40
25
150
TA (°C)
–40
25
150
TA (°C)
–40
25
150
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
A1122 Magnetic Characteristics
- 60 - 40 - 20 0 20 40 60 80 100 120 140 160 2 6 10 14 18 22 26
26
- 60 - 40 - 20 0 20 40 60 80 100 120 140 160 2 6 10 14 18 22
- 60 - 40 - 20 0 20 40 60 80 100 120 140 160 2 6 10 14 18 22 26
10
15
20
25
30
35
40
200
190
180
170
160
150
140
130
120
200
190
180
170
160
150
140
130
120
190
180
170
160
150
140
130
120
110
190
180
170
160
150
140
130
120
110
10
15
20
25
30
35
40
Operate Point versus Average Supply VoltageOperate Point versus Ambient Temperature
Release Point versus Average Supply VoltageRelease Point versus Ambient Temperature
Switchpoint Hysteresis versus Supply Voltage
Switchpoint Hysteresis versus Ambient Temperature
TA (°C)
BOP (G)
BOP (G)
BRP (G)
BRP (G)
BHYS (G)
BHYS (G)
VCC (V)
TA (°C) VCC (V)
TA (°C) V
CC
(
V
)
VCC (V)
3.0
12
24
VCC (V)
3.0
12
24
VCC (V)
3.0
12
24
TA (°C)
–40
25
150
TA (°C)
–40
25
150
TA (°C)
–40
25
150
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
CBYP
A112x
VOUT
GND
0.1 μF
VCC
Output
RL
VS
Operation
The output of the A1120, A1121, and A1122 devices switches
low (turns on) when a magnetic field perpendicular to the Hall
element exceeds the operate point threshold, BOP (see panel A of
figure 1). When the magnetic field is reduced below the release
point, BRP , the device output goes high (turns off). The output
of the A1125 devices switches high (turns off) when a magnetic
field perpendicular to the Hall element exceeds the operate point
threshold, BOP (see panel B of figure 1). When the magnetic field
is reduced below the release point, BRP , the device output goes
low (turns on).
After turn-on, the output voltage is VOUT(SAT)
. The output tran-
sistor is capable of sinking current up to the short circuit current
limit, IOM, which is a minimum of 30 mA.
The difference in the magnetic operate and release points is the
hysteresis, BHYS , of the device. 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 the hysteresis range (less than BOP and higher than BRP) will
give an indeterminate output state. The correct state is attained
after the first excursion beyond BOP or BRP
.
Applications
It is strongly recommended that an external bypass capacitor be
connected (in close proximity to the Hall element) between the
supply and ground of the device to reduce external noise in the
application. As is shown in panel B of figure 1, a 0.1 μF capacitor
is typical.
Extensive applications information for Hall effect devicers is
available in:
• Hall-Effect IC Applications Guide, Application Note 27701
• Guidelines for Designing Subassemblies Using Hall-Effect
Devices, Application Note 27703.1
• Soldering Methods for Allegro’s Products – SMT and Through-
Hole, Application Note 26009
All are provided in Allegro Electronic Data Book, AMS-702, and
the Allegro Web site, www.allegromicro.com.
Figure 1. Device switching behavior. In panels A and B, on the horizontal axis, the B+ direction indicates increasing south polarity magnetic field strength.
This behavior can be exhibited when using an electrical circuit such as that shown in panel C.
(A) (B) (C)
Functional Description
BOP
BRP
BHYS
VCC
VOUT
VOUT(SAT)
Switch to Low
Switch to High
B+
V+
0
0
BOP
BRP
BHYS
VCC
VOUT
VOUT(SAT)
Switch to Low
Switch to High
B+
V+
0
0
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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 ele-
ment. 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 Cancellation, 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 spectrum 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. This configuration is illus-
trated in figure 2.
The chopper stabilization technique uses a 400 kHz high fre-
quency clock. For demodulation process, a sample and hold
technique is used, where the sampling is performed at twice the
chopper frequency (800 kHz). This high-frequency operation
allows a greater sampling rate, which results in higher accuracy
and faster signal-processing capability. This approach desensi-
tizes 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.
The repeatability of magnetic field-induced switching is affected
slightly by a chopper technique. However, the Allegro high
frequency 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 fields; for example, speed
sensing of ring-magnet targets. For such applications, Allegro
recommends its digital device families with lower sensitivity
to jitter. For more information on those devices, contact your
Allegro sales representative.
Figure 2. Model of chopper stabilization technique
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Power Derating
The device must be operated below the maximum junction
temperature of the device, TJ(max). Under certain combinations of
peak conditions, reliable operation may require derating supplied
power or improving the heat dissipation properties of the appli-
cation. This section presents a procedure for correlating factors
affecting operating TJ. (Thermal data is also available on the
Allegro MicroSystems website.)
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.
PD = VIN × IIN (1)
T = PD × RJA (2)
TJ = TA + ΔT (3)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 1.6 mA, and RJA = 165 °C/W, then:
P
D = VCC × ICC = 12 V × 1.6 mA = 19 mW
T = PD × RJA = 19 mW × 165 °C/W = 3°C
T
J = TA + T = 25°C + 3°C = 28°C
A worst-case estimate, PD(max), represents the maximum allow-
able power level (VCC(max), ICC(max)), without exceeding TJ(max),
at a selected RJA and TA.
Example: Reliability for VCC at TA =
150°C, package LH, using a
minimum-K PCB.
Observe the worst-case ratings for the device, specifically:
RJA
=
228°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 ÷ 228 °C/W = 66 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 66 mW ÷ 4 mA = 16.5 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 reli-
able 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 conditions.
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
13
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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
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
Branded Face
CStandard Branding Reference View
N = Last two digits of device part number
T = Temperature code (letter)
1
NNT
N = Last three digits of device part number
1
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. 802840)
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
Package LH, 3-Pin (SOT-23W)
A1120 only
A1120, A1121,
A1122, and
A1125
Chopper Stabilized Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
14
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 two digits of device part number
T = Temperature code
NNT
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 Precision Hall Ef fect Switches
A1 120, A1 121, A1122
and A1 125
15
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Copyright ©2009-2012, 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
Rev. 14 May 24, 2012 Update LH package branding
