A3211
and
A3212
Micropower, Ultrasensitive
Hall Effect Switch
FUNCTIONAL DESCRIPTION (cont'd)
Operation.
The output of the A3212 switches low (turns on)
when a magnetic field perpendicular to the Hall sensor exceeds
the operate point B
OPS
(or is less than B
OPN
). After turn-on, the
output is capable of sinking up to 1 mA and the output voltage
is V
OUT(ON)
. When the magnetic field is reduced below the
release point B
RPS
(or increased above B
RPN
), the device output
switches high (turns off). The difference in the magnetic operate
and release points is the hysteresis (B
hys
) of the device. This
built-in hysteresis allows clean switching of the output even
in the presence of external mechanical vibration and electrical
noise. The A3211 functions in the same manner, except the out-
put voltage is reversed from the A3212, as shown in the figures
to the right.
As used here, negative flux densities are defined as less than
zero (algebraic convention), i.e., -50 G is less than +10 G.
Applications.
Allegro's pole-independent sensing technique
allows for operation with either a north pole or south pole mag-
net orientation, enhancing the manufacturability of the device.
The state-of-the-art technology provides the same output polarity
for either pole face.
It is strongly recommended that an external bypass capacitor
be connected (in close proximity to the Hall sensor) between the
supply and ground of the device to reduce both external noise
and noise generated by the chopper-stabilization technique. This
is especially true due to the relatively high impedance of battery
supplies.
The simplest form of magnet that will operate these devices
is a bar magnet with either pole near the branded surface of the
device. Many other methods of operation are possible. Exten-
sive applications information for Hall-effect sensors is available
in:
•
Hall-Effect IC Applications Guide,
Application Note 27701;
•
Hall-Effect Devices: Soldering, Gluing, Potting, Encapsu-
lating, and Lead Forming,
Application Note 27703.1;
•
Soldering of Through-Hole Hall-Sensor Dervices,
Application
Note 27703; and
•
Soldering of Surface-Mount Hall-Sensor Devices,
Application
Note 27703.2.
All are provided at
A3211
5V
MAX
OUTPUT OFF
BRPN
B
RPS
OUTPUT OFF
OUTPUT VOLTAGE
B OPN
0
-B
OUTPUT ON
B OPS
0
+B
MAGNETIC FLUX
A3212
5V
MAX
OUTPUT OFF
B OPN
B OPS
OUTPUT VOLTAGE
OUTPUT ON
0
-B
BRPN
BRPS
OUTPUT ON
+B
0
MAGNETIC FLUX
OUT P UT
2
DD
V
1
X
www.allegromicro.com
50 k
3
S UP P LY
(3 V B AT T E R Y )
0.1
∝F
Dwg. E H-013-2
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
8
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
