A3240ELH Allegro MicroSystems, A3240ELH Datasheet - Page 8

• Manufacturer Part Number: A3240ELH
• Description: CHOPPER-STABILIZED/ PRECISION HALL-EFFECT SWITCH
• Manufacturer: Allegro MicroSystems

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
cancellation 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 dependen-
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 Sensor Using Dynamic Quadrature Offset Cancellation
and Technical Paper STP 99-1, Chopper-Stabilized Amplifiers
With A Track-and-Hold Signal Demodulator.
on) when a magnetic field perpendicular to the Hall sensor
exceeds the operate point threshold (B
output is capable of sinking 25 mA and the output voltage is
V
sufficient strength towards the branded surface of the device
will turn the device on; removal of the south pole will leave the
device on. When the magnetic field is reduced below the
release point (B
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.
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.
is a ring magnet. Other methods of operation, such as linear
magnets, are possible. Extensive applications information on
magnets and Hall-effect sensors is also available in the Allegro
Electronic Data Book AMS-702 or Application Note 27701, or
OUT(SAT)
3240
CHOPPER-STABILIZED,
PRECISION
HALL-EFFECT SWITCH
More detailed descriptions of the circuit operation can be
The simplest form of magnet that will operate these devices
. Note that the device latches; that is, a south pole of
hys
The output of these devices switches low (turns
) of the device. This built-in hysteresis allows
RP
It is strongly recommended that an external
), the device output goes high (turns off). The
www.allegromicro.com
The Hall element can be
OP
). After turn-on, the
X
+V
+V
0
0
B
V
CC
Dwg. AH-011-2
HALL
VOLTAGE
REG
B
RP
—
+
FLUX DENSITY
X
B
OP
0.1 µF
SUPPLY
V
OUT(SAT)
Dwg. GH-007-2
Dwg. EH-013
OUTPUT
SUPPLY
+B
Dwg. EH-012