A3245 ALLEGRO [Allegro MicroSystems], A3245 Datasheet - Page 8

• Manufacturer Part Number: A3245
• Description: Chopper-Stabilized Omnipolar Hall-Effect Switches
• Manufacturer: ALLEGRO [Allegro MicroSystems]

Operation
The output of this device switches low (turns on) when a mag-
netic fi eld perpendicular to the Hall sensor exceeds the operate
point, B
voltage is V
ing current up to the short circuit current limit, I
minimum of 30 mA. When the magnetic fi eld is reduced below
the release point, B
output switches high (turns off). The difference in the magnetic
operate and release points is the hysteresis, B
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 a hysteresis region, between B
and B
is attained after the fi rst excursion beyond B
Applications
It is strongly recommended that an external bypass capacitor be
connected (in close proximity to the Hall sensor) between the
Figure 1: Switching Behavior of Omnipolar Switches. In Panel A, on the horizontal axis, the B+ direction indicates increasing south polarity
magnetic fi eld strength, and the B– direction indicates decreasing south polarity fi eld strength (including the case of increasing north
polarity). This behavior can be exhibited when using a circuit such as that shown in panel B.
A3245-DS, Rev. 1
V+
RPX
0
B–
OPS
, allows an indeterminate output state. The correct state
OUT(SAT)
(or is less than B
B
HYS
RPS
. The output transistor is capable of sink-
(or increased above B
OPN
(A)
0
Chopper-Stabilized Omnipolar Hall Effect Switches
). After turn-on, the output
B
HYS
OPX
RPN
HYS
OM
or B
), the device
, of the device.
Functional Description
, which is a
B+
RPX
V
V
.
OPX
S
OUT(SAT)
A3245
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 fi gure 1, a 0.1μF capacitor is typical.
Omnipolar switches allow operation with either a north pole or
south pole magnet orientation, enhancing product manufactur-
ability with the device.
Extensive applications information on magnets and Hall-effect
sensors is available in:
• Hall-Effect IC Applications Guide, AN27701,
• Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead
• Soldering Methods for Allegro’s Products – SMT and Through-
All are provided in Allegro Electronic Data Book, AMS-702 and
the Allegro Web site: www.allegromicro.com
Welding and Lead Forming, AN27703.1
Hole, AN26009
V
S
C
0.1 μF
BYP
A3245
(B)
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
VCC
GND
VOUT
R
LOAD
Sensor Output
8