A1220 ALLEGRO [Allegro MicroSystems], A1220 Datasheet - Page 9

• Manufacturer Part Number: A1220
• Description: Chopper Stabilized Precision Hall Effect Latches
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A1220, A1221
and A1222
Operation
The output of these devices switches low (turns on) when a mag-
netic field perpendicular to the Hall element exceeds the operate
point threshold, B
output voltage is V
sinking current up to the short circuit current limit, I
a minimum of 30 mA. When the magnetic field is reduced below
the release point, B
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.
Removal of the magnetic field will leave the device output
latched on if the last crossed switchpoint is B
the last crossed switch point is B
Powering-on the device in the hysteresis range (less than B
higher than B
rect state is attained after the first excursion beyond B
Figure 1. Switching behavior of latches. In panel A, on the horizontal axis, the B+ direction indicates increasing south polarity magnetic field strength,
and the B– direction indicates decreasing south polarity field strength (including the case of increasing north polarity). This behavior can be exhibited
when using a circuit such as that shown in panel B.
HYS ,
RP
V+
0
) will give an indeterminate output state. The cor-
B–
OP
of the device. This built-in hysteresis allows
OUT(SAT)
RP
(see panel A of figure 1). After turn-on, the
, the device output goes high (turns off).
. The output transistor is capable of
B
(A)
HYS
0
RP
.
Chopper Stabilized Precision Hall Effect Latches
B+
V
V
OP
CC
OUT(SAT)
, or latched off if
Functional Description
OM
OP
, which is
or B
OP
RP
and
.
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 both external noise
and noise generated by the chopper stabilization technique. 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 in Allegro Electronic Data Book, AMS-702, and
the Allegro Web site, www.allegromicro.com.
C
0.1 μF
V
BYP
S
A122x
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
GND
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
VCC
(B)
VOUT
R
L
Output
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