3421 Datasheet, PDF (7/12 Pages) Allegro MicroSystems – HALL-EFFECT, DIRECTION-DETECTION SENSORS

3421 AND 3422
HALL-EFFECT,
DIRECTION-DETECTION
SENSORS
FUNCTIONAL DESCRIPTION
The integrated circuit contains an internal voltage regula-
tor that powers the Hall sensors and both the analog and
digital circuitry. This regulator allows operation over a
wide supply voltage range and provides some immunity to
supply noise. The device also contains CMOS logic
circuitry that decodes the direction of rotation of the ring
magnet.
Quadrature/Direction Detection. Internal logic
circuitry provides outputs representing speed and direction
of the magnetic field across the face of the package. For
the direction signal to be appropriately updated, a quadra-
ture relationship must be maintained between the ring
magnet pole width*, the sensor-to-sensor spacing, and, to a
lesser extent, the magnetic switch points. For optimal
design, the sensor should be actuated with a ring magnet
pole width* two times the sensor-to-sensor spacing. This
will produce a sinusoidal magnetic field whose period
(denoted as Τ) is then four times the sensor-to-sensor
spacing. A quadrature relationship can also be maintained
for a ring magnet that has a period that satisfies the rela-
tionship nΤ/4 = 1.5 mm, where n is any odd integer.
Therefore, ring magnets with pole-pair spacings equal to 6
mm (n = 1), 2 mm (n = 3), 1.2 mm (n = 5), etc. are permit-
ted.
The response of the device to the magnetic field
produced by a rotating ring magnet is shown on page 2.
Note the phase shift between the two integrated sensors.
Outputs. The device provides three saturated outputs:
DIRECTION, E1 OUTPUT, and SPEED. DIRECTION
provides the direction output of the sensor and is defined
as OFF (high) for the direction E1 to E2 and ON (low) for
the direction E2 to E1. SPEED provides an XOR’d output
of the two sensors. Because of internal delays, DIREC-
TION will always be updated before SPEED and is
updated at every transition of E1 OUTPUT and E2 OUT-
PUT (internal) allowing the use of up-down counters
without the loss of pulses.
Power-On State. At power on, the logic circutry is reset
to provide an OFF (high) at DIRECTION and an OFF
(high) for E1 and E2 (internal) for magnetic fields less
than B_OP. This eliminates ambiguity when the device is
powered up and either sensor detects a field between B_OP
and B_RP. If either sensor is subjected to a field greater than
B_OP, the internal logic will set accordingly.
* “Pole” refers to a single pole (North or South) unless
stated as “pole pair” (North and South).
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