A1121 ALLEGRO [Allegro MicroSystems], A1121 Datasheet - Page 9

• Manufacturer Part Number: A1121
• Description: Chopper Stabilized Precision Hall Effect Switches
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A1120, A1121
Operation
The output of the A1120 and A1121 devices switches low (turns
on) when a magnetic field perpendicular to the Hall element
exceeds the operate point threshold, B
1). When the magnetic field is reduced below the release point,
B
A1125 devices switches high (turns off) when a magnetic field
perpendicular to the Hall element exceeds the operate point
threshold, B
is reduced below the release point, B
low (turns on).
sistor is capable of sinking current up to the short circuit current
limit, I
The difference in the magnetic operate and release points is the
hysteresis, B
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 B
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.
and A1125
After turn-on, the output voltage is V
RP
V+
, the device output goes high (turns off). The output of the
0
0
OM
, which is a minimum of 30 mA.
OP
HYS ,
(see panel B of figure 1). When the magnetic field
B
(A)
HYS
of the device. This built-in hysteresis allows
B+
V
V
Chopper Stabilized Precision Hall Effect Switches
OP
CC
OUT(SAT)
RP
OUT(SAT)
and higher than B
OP
, the device output goes
(see panel A of figure
. The output tran-
V+
0
0
Functional Description
RP
) will
B
(B)
HYS
give an indeterminate output state. The correct state is attained
after the first excursion beyond B
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 devicers 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 in Allegro Electronic Data Book, AMS-702, and
the Allegro Web site, www.allegromicro.com.
B+
V
V
CC
OUT(SAT)
V
S
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
C
0.1 μF
BYP
OP
or B
A112x
RP
VCC
GND
.
(C)
VOUT
Output
R
L
9