A3422EKA-T(2009) Просмотр технического описания (PDF) - Allegro MicroSystems

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A3422EKA-T
(Rev.:2009)

Hall Effect Direction Detection Sensor IC

Allegro MicroSystems 

3422

HALL-EFFECT,

DIRECTION-DETECTION

SENSOR IC

Functional Description

The integrated circuit contains an internal voltage regula-

tor that powers the Hall elements 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 element-to-element spacing, and,

to a lesser extent, the magnetic switch points. For optimal

design, the device 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 element-to-element

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 elements.

Outputs. The device provides three saturated outputs:

DIRECTION, E1 OUTPUT, and SPEED. DIRECTION

provides the direction output of the device 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 elements. 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 BOP. This eliminates ambiguity when the device is

powered up and either element detects a field between BOP

and BRP. If either element is subjected to a field greater than

BOP, the internal logic will set accordingly.

*“Pole” refers to a single pole (North or South) unless

stated as “pole pair” (North and South).

, Box 15036

6

Worcester, Massachusetts 01615-0036 (508) 853-5000

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