3425 Datasheet, PDF (7/12 Pages) Allegro MicroSystems – DUAL, CHOPPER-STABILIZED, ULTRA-SENSITIVE, BIPOLAR HALL-EFFECT SWITCH

3425
DUAL, CHOPPER-STABILIZED,
ULTRA-SENSITIVE,
BIPOLAR HALL-EFFECT SWITCH
FUNCTIONAL DESCRIPTION
Chopper-Stabilized Technique. 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 dependencies, and
thermal stress. 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.
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.
The chopper-stabilizing technique cancels the mismatch-
ing of the resistors by changing the direction of the current
flowing through the Hall plate and Hall voltage measure-
ment taps, while maintaining the Hall-voltage signal that
is induced by the external magnetic flux. The signal is,
then, captured by a sample-and-hold circuit.
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 low
(turns on) when a magnetic field perpendicular to the Hall
sensor exceeds the operate point threshold (B_OP). After
turn-on, the output is capable of sinking 30 mA and the
output voltage is V_OUT(SAT). When the magnetic field is
reduced below the release point (B_RP), the device output
switches high (turns off). Note especially that release can
occur when the magnetic field is removed but to ensure
release, a field reversal is required. 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.
REG
X
B
+V
+V
V_CC
—
HALL
VOLTAGE
+
Dwg. AH-011-2
Dwg. EH-012
0
-B
B _RP
B _OP
0
FLUX DENSITY
V_OUT(SAT)
+B
Dwg. GH-034-5
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