A1145 and A1146
Ultrasensitive Two-Wire Chopper-Stabilized
Unipolar Hall Effect Switches
The A1145 and A1146 devices are two-wire, unipolar, Hall effect switches that are
factory-programmed at end-of-line to optimize ultrasensitive magnetic switchpoint
accuracy. These devices use a patented high frequency chopper-stabilization tech-
nique, produced using the Allegro advanced BiCMOS wafer fabrication process,
to achieve magnetic stability and to eliminate offset inherent in single-element
devices exposed to harsh application environments.
≈1:1
Package LH, 3-pin SOT
Package UA, 3-pin SIP
Commonly found in a number of automotive applications, these switches are
utilized to sense seat track position, seat belt buckle presence, hood/trunk latch-
ing, and shift selector position. Two-wire unipolar switches, such as the A1145
and A1146, are particularly advantageous in price-sensitive applications because
they require one less wire for operation than do switches with the more traditional
open-collector output. Additionally, the system designer inherently gains diagnos-
tics because there is always output current flowing, which should be in either of
two narrow ranges. Any current level not within these ranges indicates a fault con-
dition. These devices also feature on-chip transient protection and a Zener clamp
to protect against overvoltage conditions on the supply line.
The output currents of the A1146 switches HIGH in the presence of a south (+)
polarity magnetic field of sufficient strength, and switches LOW otherwise, as in
the presence of a weak field or a north (–) polarity field. The A1145 has an oppo-
site output: the currents switch LOW in the presence of a south-polarity magnetic
field of sufficient strength, and switch HIGH otherwise.
Both versions are offered in two package styles. The LH is a SOT-23W, miniature
low-profile package for surface-mount applications. The UA is a three-lead ultra-
mini SIP for through-hole mounting. Each package is available in a lead (Pb) free
version (suffix,
–T)
with 100% matte tin plated leadframe. Field-programmable
versions also available: A1185 and A1186.
≈1:1
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
CC
...........................................28V
Reverse-Supply Voltage, V
RCC
........................
–18 V
Magnetic Flux Density, B .........................Unlimited
Power Dissipation, P
D
............................
Graph, p. 5
Operating Temperature
Ambient, T
A
, Range E..................
–40ºC to 85ºC
Ambient, T
A
, Range L................
–40ºC to 150ºC
Maximum Junction, T
J(max)
........................165ºC
Storage Temperature, T
S
..................
–65ºC to 170ºC
Features and Benefits
Chopper stabilization
Low switchpoint drift over operating
temperature range
Low sensitivity to stress
Factory programmed at end-of-line for
optimized switchpoints
On-chip protection
Supply transient protection
Reverse-battery protection
On-board voltage regulator
3.5 to 24 V operation
A1145-DS, Rev. 3
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A1145 and A1146
Ultrasensitive Two-Wire Chopper-Stabilized Unipolar Hall Effect Switches
Functional Block Diagram
V+
VCC
Regulator
To All Subcircuits
Clock/Logic
0.01 uF
Sample and Hold
Dynamic Offset
Cancellation
Low-Pass
Filter
Amp
GND
Package UA Only
GND
Package LH, 3-pin SOT
Package UA, 3-pin SIP
3
PTCT
NC
1. VCC
2. No connection
3. GND
1
2
1. VCC
2. GND
3. GND
1
2
3
A1145-DS, Rev. 3
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
A1145 and A1146
Ultrasensitive Two-Wire Chopper-Stabilized Unipolar Hall Effect Switches
ELECTRICAL CHARACTERISTICS
over the operating voltage and temperature ranges, unless otherwise specified
Characteristic
Supply Voltage
1
Supply Current
2
Reverse Supply Current
Supply Zener Clamp Voltage
Supply Zener Clamp Current
3
Output Slew Rate
4
Chopping Frequency
Power-On Time
5
Power-On State
6,7
1
V
CC
represents
2
Relative values
Symbol
V
CC
I
CCL
I
CCH
I
RCC
V
ZSUPPLY
I
ZSUPPLY
di/dt
f
C
t
on
POS
Test Conditions
Min.
3.5
Typ.
–
–
–
–
–
–
36
200
–
HIGH
Max.
24
6.9
17
–1.2
40
10
–
–
25
–
Units
V
mA
mA
mA
V
mA
mA/µs
kHz
µs
–
B > B
OP
for A1145
B > B
OP
for A1146
V
CC
= –18 V
I
CC
= I
CCL(max)
+ 3 mA; T
A
= 25°C
V
ZSUPPLY
= 28 V
Capacitance of the oscilloscope performing
the measurement = 20 pF
5
12
–
28
–
–
–
C
BYPASS
= 0.01 µF
–
–
t < t
on
;
V
CC
slew rate > 25 mV/µs
the generated voltage between the VCC pin and the GND pin.
of B use the algebraic convention, where positive values indicate south magnetic polarity, and negative values indicate north magnetic
polarity; therefore greater B values indicate a stronger south polarity field (or a weaker north polarity field, if present).
3
I
ZSUPPLY(max)
= I
CCL(max)
+ 3 mA.
4
Measured without bypass capacitor between VCC and GND. Use of a bypass capacitor results in slower current change.
5
Measured with and without bypass capacitor of 0.01 µF. Adding a larger bypass capacitor causes longer Power-On Time.
6
POS is defined as true only with a V
CC
slew rate of 25 mV / µs or greater. Operation with a V
CC
slew rate less than 25 mV / µs can permanently harm
device performance.
7
POS is undefined when power-on occurs at t > t or when B
on
RP
< B < B
OP
.
MAGNETIC CHARACTERISTICS
over the operating voltage and temperature ranges, unless otherwise specified
Characteristic
Operate Point
Symbol
B
OP
A1145
A1146
A1145
A1146
Test Conditions
I
CC
= I
CCL
I
CC
= I
CCH
I
CC
= I
CCH
I
CC
= I
CCL
Min.
20
Typ.*
37
Max.
60
Units
G
Release Point
Hysteresis
*Typical data taken at T
A
= 25°
B
RP
B
HYS
10
5
22
15
55
30
G
G
B
HYS
= B
OP
– B
RP
A1145-DS, Rev. 3
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
A1145 and A1146
Ultrasensitive Two-Wire Chopper-Stabilized Unipolar Hall Effect Switches
Characteristic Data
Supply Current (Low) versus Ambient Temperature
at Various Levels of V
CC
(A1145 and A1146)
10
8
Supply Current (High) versus Ambient Temperature
at Various Levels of V
CC
(A1145 and A1146)
20
18
V
CC
3.5 V
12.0 V
24.0 V
I
CCH
(mA)
I
CCL
(mA)
6
4
2
0
–50
16
14
12
10
–50
V
CC
3.5 V
12.0 V
24.0 V
0
50
100
150
200
0
50
100
150
200
Ambient Temperature, T
A
(°C)
Ambient Temperature, T
A
(°C)
Operate Point versus Ambient Temperature
at Various Levels of V
CC
(A1145 and A1146)
70
60
50
Switchpoint Hysteresis versus Ambient Temperature
at Various Levels of V
CC
(A1145 and A1146)
40
35
30
V
CC
B
HYS
(G)
3.5 V
12.0 V
24.0 V
25
20
15
10
5
V
CC
3.5 V
12.0 V
24.0 V
B
OP
(G)
40
30
20
10
0
–50
0
50
100
150
200
0
–50
0
50
100
150
200
Ambient Temperature, T
A
(°C)
Ambient Temperature, T
A
(°C)
A1145-DS, Rev. 3
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
A1145 and A1146
Ultrasensitive Two-Wire Chopper-Stabilized Unipolar Hall Effect Switches
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
Test Conditions
Package LH, minimum-K PCB (single layer, single-sided with
copper limited to solder pads)
Package LH, low-K PCB (single layer, double-sided with
0.926 in
2
copper area)
Package UA, minimum-K PCB (single layer, single-sided with
copper limited to solder pads)
Value Units
110
228
165
ºC/W
ºC/W
ºC/W
Package Thermal Resistance
R
θJA
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
20
Power Derating Curve
T
J(max)
= 165ºC; I
CC
= I
CC(max)
V
CC(max)
Maximum Allowable V
CC
(V)
Low-K PCB, Package LH
(R
θJA
= 110 ºC/W)
Minimum-K PCB, Package UA
(R
θJA
= 165 ºC/W)
Minimum-K PCB, Package LH
(R
θJA
= 228 ºC/W)
V
CC(min)
140
160
180
40
60
80
100
120
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
20
Power Dissipation, P
D
(m W)
Lo
(R w-K
PC
θ
J
A
=
11 B, P
0 º ac
Min
C/ ka
W ge
(R imum
)
LH
-K
θ
JA
=
165 PCB
, Pa
ºC/
cka
W)
ge
UA
Min
imu
m-K
(R
P
θ
JA
=
228 CB, Pa
ºC/W
ckag
e LH
)
40
60
80
100
120
Temperature (°C)
140
160
180
A1145-DS, Rev. 3
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5
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