A3240ELTTR Allegro Microsystems Inc, A3240ELTTR Datasheet - Page 8

• Manufacturer Part Number: A3240ELTTR
• Description: IC SWITCH HALL EFFECT SOT-89
• Manufacturer: Allegro Microsystems Inc
• Type: Special Purposer

Specifications of A3240ELTTR

• Sensing Range: 50G Trip, 5G Release
• Voltage - Supply: 4.2 V ~ 24 V
• Current - Supply: 6mA
• Current - Output (max): 25mA
• Output Type: Digital, Open Collector
• Features: Regulated Voltage
• Operating Temperature: -40°C ~ 85°C
• Package / Case: SOT-89-3
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A3240
Chopper-Stabilized Technique. The Hall element can be
considered as a resistor array similar to a Wheatstone bridge. A
large portion of the offset is a result of the mismatching of these
resistors. These devices use a proprietary dynamic offset cancel-
lation technique, with an internal high-frequency clock to reduce
the residual offset voltage of the Hall element that is normally
caused by device overmolding, temperature de pen den cies, and
thermal stress. The chopper-stabilizing technique cancels the
mismatching of the resistor circuit by changing the direction of
the current flowing through the Hall plate using CMOS switches
and Hall voltage measurement taps, while maintaing the Hall-
voltage signal that is induced by the external magnetic flux. The
signal is then captured by a sample-and-hold circuit and further
processed using low-offset bipolar circuitry. This technique
produces devices that have an extremely stable quiescent Hall
output voltage, are immune to thermal stress, and have precise
recoverability after temperature cycling. This technique will
also slightly degrade the device output repeatability. A relatively
high sampling frequency is used in order that faster signals can
be processed.
found in: Technical Paper STP 97-10, Monolithic Magnetic Hall
Sensing Using Dynamic Quadrature Offset Cancellation and
Technical Paper STP 99-1, Chopper-Stabilized Amplifiers With A
Track-and-Hold Signal Demodulator.
Operation. The output of these devices switch es low (turns
on) when a magnetic field (south pole) perpendicular to the
Hall element exceeds the operate point threshold (B
turn-on, the output is capable of sinking 25 mA and the output
voltage is V
the release point (B
The dif fer ence 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.
Applications. It is strongly recommended that an external
bypass capacitor be con nect ed (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-sta bi li za-
tion technique.
is a ring magnet. Oth er meth ods of operation, such as linear
magnets, are possible. Extensive ap pli ca tions in for ma tion on
magnets and Hall-effect devices is also available in Application
Note 27701, or at
More detailed descriptions of the circuit operation can be
The sim plest form of magnet that will op er ate these devices
OUT(SAT)
hys
) of the device. This built-in hysteresis allows
RP
www.allegromicro.com
. When the magnetic field is reduced below
), the device output goes high (turns off).
Chopper-Stabilized, Precision Hall-Effect Switch
FUNCTIONAL DESCRIPTION
OP
). After
+V
X
+V
0
0
B
V
CC
Dwg. AH-011-2
HALL
VOLTAGE
REG
B
RP
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
—
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
+
FLUX DENSITY
X
B
OP
0.1 F
SUPPLY
V
OUT(SAT)
Dwg. GH-007-2
Dwg. EH-013
OUTPUT
+B
Dwg. EH-012
SUPPLY
7