3250
PROGRAMMABLE, CHOPPER-
STABILIZED, PRECISION,
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 repeatabil-
ity.
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 the A3250x switches low (turns on)
when a magnetic field (south pole) perpendicular to the Hall
sensor exceeds the operate point threshold (B
OP
). After turn-on,
the output is capable of sinking 20 mA and the output voltage is
V
OUT(SAT)
. The A3250x
operate point
is programmable (see
next section). When the magnetic field is reduced below the
release point (B
RP
), the device output goes high (turns off).
REG
X
B
+V
—
HALL
VOLTAGE
+
Dwg. AH-011-2
A3250x OUTPUT CHARACTERISTIC
+V
V
CC
OUTPUT VOLTAGE
B
RP
B
OP
V
OUT(SAT)
0
0
FLUX DENSITY
+B
Dwg. GH-007-2
www.allegromicro.com
SAMPLE
& HOLD
Dwg. EH-012
5
SANKEN [ SANKEN ELECTRIC ]
