3260
2-WIRE, CHOPPER-STABILIZED,
PRECISION HALL-EFFECT
BIPOLAR SWITCH
www.allegromicro.com
5
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 repeat-
ability.
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 mismatching of the resistors by
changing the direction of the current flowing through the Hall
plate and Hall voltage measurement 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.
Operation. The output of these devices turns ON when a
magnetic field (north pole) perpendicular to the Hall element
exceeds the release point threshold (B
RP
). After turn-ON, the
output will source current equal to the device operating current
plus a current source (I
GND(H)
). When the magnetic field is
increased (south pole) above the operate point (B
OP
), the output
will source current equal to the device operating
current with the current source turned OFF (I
GND(L)
). 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. The hysteresis allows clean
switching of the output even in the presence of external me-
chanical vibration or electrical noise.
Powering up in the absence of a magnetic field (less than
B
OP
and higher than B
RP
) will allow an indeterminate output
state. The correct state is warranted after the first excursion
beyond B
OP
or B
RP
.
Bipolar switches
may switch on removal of field but
require field reversal for reliable operation over temperature
range; latches will
not switch on removal of magnetic field.
Dwg. EH-012
REG
X
+V
HALL
VOLTAGE
B
+
Dwg. AH-011-2
0
+B
0
FLUX DENSITY
Dwg. GH-034-6
-B
+I
IOUT + ICC
BRP
BOP
ICC