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 sensor 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
Package: 3 pin SOT89 (suffix LT) and
3 pin SIP (suffix UA)
Continued on the next page…
Not to scale
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. 3
A3250
and
A3251
Field-Programmable, Chopper-Stabilized,
Unipolar Hall-Effect Switches
Three package styles provide a magnetically optimized package
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)
field drops below the magnetic release point, B
RP
. The output 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
.
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.
Selection Guide
Part Number
A3250ELT-T
A3250ELTTR-T
A3250EUA-T
A3250LLT-T
A3250LLTTR-T
A3250LUA-T
A3251ELT-T
A3251ELTTR-T
A3251EUA-T
A3251LLT-T
A3251LLTTR-T
A3251LUA-T
1
Pb-based
Pb-free
1
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Packing
2
Bulk, 500 pieces/bag
7-in. reel, 1000 pieces/reel
Bulk, 500 pieces/bag
Bulk, 500 pieces/bag
7-in. reel, 1000 pieces/reel
Bulk, 500 pieces/bag
Bulk, 500 pieces/bag
7-in. reel, 1000 pieces/reel
Bulk, 500 pieces/bag
Bulk, 500 pieces/bag
7-in. reel, 1000 pieces/reel
Bulk, 500 pieces/bag
Package
Surface mount
SIP through hole
Surface mount
SIP through hole
Surface mount
SIP through hole
Surface mount
SIP through hole
T
A
(ºC)
–40 to 85
V
OUT
Power-On
High
Running
3
Low
–40 to 150
High
Low
–40 to 85
Low
High
–40 to 150
Low
High
variants are being phased out of the product line.
a.
Certain variants cited in this footnote are in production but have been determined to be LAST TIME BUY. This classification indicates that sale of this
device is currently restricted to existing customer applications. The device should not be purchased for new design applications because obsolescence in
the near future is probable. Samples are no longer available. Status change: October 31, 2006. Deadlilne for receipt of LAST TIME BUY ORDERS: April
27, 2007. These variants include:
A3250ELT, A3250ELTTR, A3250EUA, A3251ELT, A3251ELTTR, A3251EUA, A3251LLT, A3251LLTTR, and
A3251LUA
.
b. Certain variants cited in this footnote are in production but have been determined to be NOT FOR NEW DESIGN. This classification
indicates that sale of this device is currently restricted to existing customer applications. The device should not be purchased for new
design applications because obsolescence in the near future is probable. Samples are no longer available. Status change: May 1, 2006.
These variants include: A3250LLT, A3250LLTTR, A3250LUA.
2
Contact Allegro for additional packing options.
3
In south polarity magnetic field of sufficient strength.
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