A1121 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
Manufacturer
A1121 Datasheet PDF : 18 Pages
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A1120, A1121, A1122,
A1123, and A1125
Chopper-Stabilized Precision Hall-Effect Switches
Functional Description
Operation
The output of the A1120, A1121, A1122, and A1123 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 devices 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 on the Allegro Web site, www.allegromicro.com.
V+
0
0
V+
VCC
VOUT(SAT)
B+
0
0
VCC
VOUT(SAT)
B+
VS
CBYP
0.1 µF
VCC
A112x
VOUT
GND
RL
Output
BHYS
BHYS
(A)
(B)
(C)
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.
Allegro MicroSystems, LLC
12
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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