A3340 Allegro MicroSystems, Inc., A3340 Datasheet - Page 7

• Manufacturer Part Number: A3340
• Description: Chopper-stabilized, Precision Hall-effect Switch
• Manufacturer: Allegro MicroSystems, Inc.

A3340
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 dependencies, 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-andhold circuit and further
processed using low-offset bipolar circuitry. This technique pro-
duces devices that have an extremely stable quiescent Hall output
voltage, are immune to thermal stress, and have precise recover-
ability 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.
More detailed descriptions of the circuit operation can be 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. Operation. The output of these devices
switches high (turns off) when a magnetic field (south pole)
perpendicular to the Hall sensor exceeds the operate point thresh-
old (B
point (B
the output is capable of sinking 25 mA and the output voltage is
V
points is the hysteresis (B
esis allows 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
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 chopperstabilization technique.
The simplest form of magnet that will operate these devices 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 Application Note 27701, or
at www.allegromicro.com.
OUT(SAT)
OP
RP
). When the magnetic field is reduced below the release
. The difference in the magnetic operate and release
), the device output goes low (turns on). After turn-on,
hys
) of the device. This built-in hyster-
Chopper-Stabilized, Precision Hall-Effect Switch
FUNCTIONAL DESCRIPTION
+V
C C
+V
0
0
B
V
OUT (S AT )
+V
–V
REG
HALL
HALL
B
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
R P
F L UX DE NS IT Y
VOUT
GND
VCC
X
B
OP
0.1 μF
SUPPLY
V
C C
Dwg. EH-013
OUTPUT
SUPPLY
+B
Dwg. EH-012
7