A3250 and A3251
Field-Programmable, Chopper-Stabilized
Unipolar Hall-Effect Switches
Discontinued Product
This device is no longer in production. The device should not be
purchased for new design applications. Samples are no longer available.
Date of status change: October 31, 2011
Recommended Substitutions:
For existing customer transition, and for new customers or new appli-
cations, contact Allegro Sales.
NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan
for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The
information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no respon-
sibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
A3250 and A3251
Field-Programmable, Chopper-Stabilized
Unipolar Hall-Effect Switches
Features and Benefits
▪
Chopper stabilization for stable switchpoints throughout
operating temperature range
▪
Externally programmable operate point (through VCC pin)
▪
On-board voltage regulator for 4.2 V to 24 V operation
▪
On-chip protection against:
▫
Supply transients
▫
Output short-circuits
▫
Reverse-battery condition
Description
The A3250 and A3251 are field-programmable, chopper-
stabilized, unipolar Hall-effect switches designed for use in
high-temperature applications. These devices use a chop-
per-stabilization technique to eliminate offset inherent in
single-element devices.
The A3250 and A3251 are externally programmable
devices. The devices have a wide range of programmabil-
ity of the magnetic operate point (B
OP
) while the hysteresis
remains fixed. This advanced feature allows for optimiza-
tion of the device switchpoint and can drastically reduce
the effects of variations found in a production environment,
such as magnet and device placement tolerances.
These devices provide on-chip transient protection. A Zener
clamp on the power supply protects against overvoltage
conditions on the supply line. These devices also include
short-circuit protection on the output.
The output of the A3250 switches LOW when subjected
to a south-polarity magnetic field with a flux density that
exceeds the threshold for B
OP
, and switches HIGH when the
field drops below the magnetic release point, B
RP
. The out-
put of the A3251 has the opposite polarity, switching HIGH
in a south-polarity magnetic field that B
OP
, and switching
LOW when the field drops below B
RP
.
Package: 3-pin SOT89 (suffix LT) and
3-pin SIP (suffix UA)
Not to scale
Continued on the next page…
Functional Block Diagram
VCC
Program/Lock
Programming
Logic
Regulator
Offset Adjust
Sample and Hold
Dynamic Offset
Cancellation
VOUT
Amp
Current Limit
Low-Pass
Filter
GND
3250-DS Rev. 11
A3250
and
A3251
Field-Programmable, Chopper-Stabilized,
Unipolar Hall-Effect Switches
for most applications. Type LT is a miniature SOT89/TO-243AA
surface mount package that is thermally enhanced with an
exposed ground tab, and type UA is a three-lead ultramini SIP
for through-hole mounting. The packages are lead (Pb) free, with
100% matte tin plated leadframes (suffix, –T).
Description (continued)
The other differences in the devices are the power-on state. The
A3250 powers-on in the HIGH state, while the A3251 powers-on
in the LOW state.
Three package styles provide a magnetically optimized package
Selection Guide
Part Number
A3250LLTTR-T
Packing
1
7-in. reel, 1000 pieces/reel
Package
Surface mount
T
A
(ºC)
–40 to 150
V
OUT
Power-On
High
Running
2
Low
1
Contact Allegro for additional packing options.
2
In south polarity magnetic field of sufficient strength.
Absolute Maximum Ratings
Characteristic
Supply Voltage
Reverse Supply Voltage
Zener Overvoltage
Output Current
Magnetic Flux Density
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
Symbol
V
CC
V
RCC
V
Z
I
OUT
B
T
A
T
J
(max)
T
stg
Range E
Range L
Notes
Rating
26.5
–18
30
20
Unlimited
–40 to 85
–40 to 150
165
–65 to 170
Units
V
V
V
mA
G
ºC
ºC
ºC
ºC
Pin-out Diagrams
Terminal List
Number
1
2
3
Name
VCC
GND
VOUT
Function
Connects power supply to chip
Ground
Device output
1
2
3
LT
1
2
3
UA
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
A3250
and
A3251
Characteristic
ELECTRICAL CHARACTERISTICS
Supply Voltage
1
Output Saturation Voltage
Output Leakage Current
V
CC
V
OUT(sat)
I
OFF
I
CC(off)
Supply Current
I
CC(on)
Output Rise Time
Output Fall Time
Chopping Frequency
Power-Up Time
Output Current Limit
1,2
Power-On State
MAGNETIC CHARACTERISTICS
Initial Operate Point
Temperature Drift of B
OP
Hysteresis (B
OP
– B
RP
)
B
OP
ΔB
OP
B
hys
t
r
t
f
f
C
t
on
I
OUT(lim)
POS
Symbol
Field-Programmable, Chopper-Stabilized,
Unipolar Hall-Effect Switches
Test Conditions
Min.
Typ.
Max.
Units
OPERATING CHARACTERISTICS
valid over operating T
A
and V
CC
, unless otherwise specified
Running mode
I
OUT
= 20 mA; Switch state = ON
V
OUT
= 24 V; Switch state = OFF
A3250; B < B
RP
; V
OUT
= HIGH
A3251; B > B
OP
; V
OUT
= HIGH
A3250; B > B
OP
; V
OUT
= LOW
A3251; B < B
RP
; V
OUT
= LOW
R
LOAD
= 820
Ω,
C
LOAD
= 10 pF
R
LOAD
= 820
Ω,
C
LOAD
= 10 pF
4.2
–
–
–
–
–
–
–
–
–
–
175
–
4.0
4.0
6.0
6.0
–
–
340
20
90
HIGH
LOW
24
400
10
7.0
7.0
10.0
10.0
5.0
5.0
–
50
120
–
–
V
mV
μA
mA
mA
mA
mA
μs
μs
kHz
μs
mA
mV
mV
V
OUT
= HIGH
Short-circuit protection
A3250; B < B
RP
, t > t
on
A3251; B < B
RP
, t > t
on
–
60
–
–
–20
B
OP
≤
500 gauss
Package T
A
range = J
Package T
A
range = L
–35
5.0
5.0
13
–
18
13
50
35
35
35
G
G
G
G
PROGRAMMING CHARACTERISTICS
Programmable B
OP
Values
3
Number of Programming Bits
Resolution
B
OP(prog)
–
B
RES
Switchpoint set
Programming lock
50
–
–
–
–
6
1
7.0
≥350
–
–
–
G
Bit
Bit
G
TRANSIENT PROTECTION CHARACTERISTICS
Supply Zener Voltage
Supply Zener Current
Reverse Battery Current
1
2
3
V
Z
I
Z
I
RCC
V
CC
= 28 V
V
RCC
= –18 V, T
J
< T
J(max)
28
–
–
–
–
–
–
13
–5.0
V
mA
mA
Do not exceed T
J
(max): Additional information on power derating is provided in the applications section.
Short-circuit protection is not intended for continuous operation; permanent damage may result.
Device can be used below 50 G but is not guaranteed to be a unipolar switch. It is the responsibility of the programmer to verify that the desired
switchpoint has been achieved.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
A3250
and
A3251
Field-Programmable, Chopper-Stabilized,
Unipolar Hall-Effect Switches
Typical Characterization Data
All data are taken with A3250 devices, the average of 3 lots, 30 pieces per lot
Average B
OP
vs. T
A
Program Code: 1, V
CC
= 12 V
30
Average B
RP
vs. T
A
Program Code: 1, V
CC
= 12 V
10
Average B
RP
(G)
-20
10
40
70
T
A
(°C)
100
130
160
Average B
OP
(G)
25
20
15
10
5
0
-5
-50
5
0
-5
-10
-15
-20
-50
-20
10
40
70
T
A
(°C)
100
130
160
Average B
OP
vs. T
A
Program Code: 8, V
CC
= 12 V
75
Average B
RP
vs. T
A
Program Code: 8, V
CC
= 12 V
60
Average B
OP
(G)
Average B
RP
(G)
70
65
60
55
50
45
40
-50
-20
10
40
70
T
A
(°C)
100
130
160
50
40
30
20
-50
-20
10
40
70
T
A
(°C)
100
130
160
Average B
OP
vs. T
A
Program Code: 16, V
CC
= 12 V
130
Average B
RP
vs. T
A
Program Code: 16, V
CC
= 12 V
110
Average B
OP
(G)
125
120
115
110
105
100
-50
-20
10
40
70
T
A
(°C)
100
130
160
Average B
RP
(G)
105
100
95
90
85
80
-50
-20
10
40
70
T
A
(°C)
100
130
160
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
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