3121, 3122,
AND
3123
HALL-EFFECT SWITCHES
FOR HIGH-TEMPERATURE OPERATION
These Hall-effect switches are monolithic integrated circuits with
tighter magnetic specifications, designed to operate continuously over
extended temperatures to +150°C, and are more stable with both tem-
perature and supply voltage changes. The unipolar switching character-
istic makes these devices ideal for use with a simple bar or rod magnet.
The three basic devices (3121, 3122, and 3123) are identical except for
magnetic switch points.
Each device includes a voltage regulator for operation with supply
voltages of 4.5 voltas to 24 volts, reverse battery protection diode,
quadratic Hall-voltage generator, temperature compensation circuitry,
small-signal amplifier, Schmitt trigger, and an open-collector output to
sink up to 25 mA. With suitable output pull up, they can be used with
bipolar or CMOS logic circuits. The 3121 is an improved replacement
for the 3113 and 3119.
The first character of the part number suffix determines the device
operating temperature range. Suffix ‘E–’ is for the automotive and
industrial temperature range of -40°C to +85°C. Suffix ‘L–’ is for the
automotive and military temperature range of -40°C to +150°C. Three
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 ‘–U’ is a three-lead
plastic mini-SIP while suffix ‘–UA’ is a three-lead ultra-mini-SIP.
Data Sheet
27621.4B*
V
X
CC
1
2
3
GROUND
Dwg. PH-003A
Pinning is shown viewed from branded side.
OUTPUT
SUPPLY
FEATURES and BENEFITS
s
Superior Temp. Stability for Automotive or Industrial Applications
s
4.5 V to 24 V Operation … Needs Only An Unregulated Supply
s
Open-Collector 25 mA Output … Compatible with Digital Logic
s
Reverse Battery Protection
s
Activate with Small, Commercially Available Permanent Magnets
s
Solid-State Reliability … No Moving Parts
s
Small Size
s
Resistant to Physical Stress
ABSOLUTE MAXIMUM RATINGS
at T
A
= +25
°
C
Supply Voltage, V
CC
...........................
30 V
Reverse Battery Voltage, V
RCC
........
-30 V
Magnetic Flux Density, B .......
Unlimited
Output OFF Voltage, V
OUT
................
28 V
Reverse Output Voltage, V
OUT
........
-0.5 V
Continuous Output Current, I
OUT
...
25 mA
Operating Temperature Range, T
A
Suffix ‘E–’ .................
-40
°
C to +85
°
C
Suffix ‘L–’ ...............
-40
°
C to +150
°
C
Storage Temperature Range,
T
S
..............................
-65
°
C to +170
°
C
The A3121xU is not for new design.
The A3122xU and A3123xU are last-time buy.
Orders accepted until April 15, 2002.
Always order by complete part number, e.g.,
A3121EU
.
3121, 3122,
AND
3123
HALL-EFFECT SWITCHES
FOR HIGH-TEMPERATURE
OPERATION
ELECTRICAL CHARACTERISTICS over operating temperature range, at V
CC
= 12 V.
Limits
Characteristic
Supply Voltage
Output Saturation Voltage
Output Leakage Current
Supply Current
Output Rise Time
Output Fall Time
Symbol
V
CC
V
OUT(SAT)
I
OFF
I
CC
t
r
t
f
Test Conditions
Operating
I
OUT
= 20 mA, B > B
OP
V
OUT
= 24 V, B < B
RP
B < B
RP
(Output OFF)
R
L
= 820
Ω,
C
L
= 20 pF
R
L
= 820
Ω,
C
L
= 20 pF
Min.
4.5
140
<1.0
4.6
0.04
0.18
Typ.
Max.
24
400
10
9.0
2.0
2.0
Units
V
mV
µA
mA
µs
µs
MAGNETIC CHARACTERISTICS in gauss over operating supply voltage range.
Part Numbers*
A3121
Characteristic
B
OP
at T
A
= 25°C
over operating temp. range
B
RP
at T
A
= 25°C
over operating temp. range
B
hys
at T
A
= 25°C
over operating temp. range
Min.
250
220
125
80
70
60
Typ.
350
350
245
245
105
105
Max.
450
500
380
410
140
150
Min.
280
260
140
120
70
70
A3122
Typ.
340
340
235
235
105
105
Max.
400
430
330
360
140
140
Min.
250
230
180
160
70
70
A3123
Typ.
345
345
240
240
105
105
Max
440
470
300
330
140
140
NOTES: Typical values are at T
A
= +25°C and V
CC
= 12 V.
B
OP
= operate point (output turns ON); B
RP
= release point (output turns OFF); B
hys
= hysteresis (B
OP
- B
RP
).
*Complete part number includes a suffix to identify operating temperature range (E- or L-) and package type ( -LT, -U, or -UA).
FUNCTIONAL BLOCK DIAGRAM
1
V
CC
REG.
X
3
OUTPUT
GROUND
2
Dwg. FH-005-2
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 1992, 1999, Allegro MicroSystems, Inc.
3121, 3122,
AND
3123
HALL-EFFECT SWITCHES
FOR HIGH-TEMPERATURE
OPERATION
SENSOR LOCATIONS
(±0.005" [0.13 mm] die placement)
Suffix “LT”
ACTIVE AREA DEPTH
0.0305"
0.775 mm
NOM
0.089"
2.26 mm
OPERATION
The output of these devices (pin 3) switches low when the mag-
netic field at the Hall sensor exceeds the operate point threshold (B
OP
).
At this point, the output voltage is V
OUT(SAT)
. When the magnetic field
is reduced to below the release point threshold (B
RP
), the device output
goes high. 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 mechani-
cal vibration and electrical noise.
0.043"
1.09 mm
A
1
2
3
APPLICATIONS INFORMATION
Hall effect applications information is available in the “Hall-Effect
IC Applications Guide”, which can be found in the latest issue of
Allegro MicroSystems Data Book
AMS-702.
Dwg. MH-008-2D
Suffix “U”
ACTIVE AREA DEPTH
0.0165"
0.42 mm
NOM
0.091"
2.31 mm
20
CHANGE IN OPERATE POINT
CHANGE IN OPERATE POINT IN GAUSS
0.070"
1.78 mm
15
T
A
= +25°C
10
A
BRANDED
SURFACE
1
2
3
5.0
Dwg. MH-002-2C
0
Suffix “UA”
ACTIVE AREA DEPTH
0.0195"
0.50 mm
NOM
0.082"
2.07 mm
-5.0
0
5
10
15
20
25
Dwg. GH-042
SUPPLY VOLTAGE IN VOLTS
A
BRANDED
SURFACE
1
2
3
0.055"
1.38 mm
Dwg. MH-011-2D
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
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