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A1642LK-DS

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

Two-Wire True Zero-Speed Miniature Differential Peak-Detecting Sensor with Continuous Calibration

A1642LK

Sensing Technology

The single-chip differential Hall effect sensor IC possesses two

Hall elements, which sense the magnetic profile of the ring mag-

net simultaneously, but at different points (spaced at a 1.5 mm

that is processed for precise switching of the digital output

signal.

The Hall IC is self-calibrating and also possesses a temperature

compensated amplifier and offset compensation circuitry. Its

voltage regulator provides supply noise rejection throughout the

operating voltage range. Changes in temperature do not greatly

affect this device due to the stable amplifier design and the offset

compensation circuitry. The Hall transducers and signal process-

ing electronics are integrated on the same silicon substrate, using

a proprietary BiCMOS process.

Target Profiling

An operating device is capable of providing digital informa-

tion that is representative of the magnetic features on a rotating

target. The waveform diagram shown in figure 3 presents the

automatic translation of the magnetic profile to the digital output

signal of the sensor.

Output Polarity

Figure 3 shows the output polarity for the orientation of target

and sensor shown in figure 2. The target direction of rotation

shown is: perpendicular to the leads, across the face of the

device, from the pin 1 side to the pin 4 side. This results in the

as the leading edge of a north magnetic pole passes the sensor

face. In this configuration, the device output current switches to

its low polarity when a north pole is the target feature nearest to

the sensor. If the direction of rotation is reversed, then the output

polarity inverts.

Note that output voltage polarity is dependent on the position of

Target

(Ring Magnet)

(Pin 1 Side)

(Pin 4 Side)

Hall IC

Element Pitch

Hall Element 1

Hall Element 2

N

N

S

S

of Sensor

Rotating Target

Branded Face

1

4

Functional Description

Figure 1. Relative motion of the target is detected by the dual Hall ele-

ments mounted on the Hall IC.

Figure 2. This left-to-right (pin 1 to pin 4) direction of target rotation

results in a low output signal when a magnetic north pole of the target is

nearest the face of the sensor (see figure 3). A right-to-left (pin 4 to pin

1) rotation inverts the output signal polarity.

Figure 4: Voltages profiles for high side and low side two-wire sensing.

Figure 3. Output Profile of a ring magnet target for the polarity

indicated in figure 2.

A1642

VCC

GND

V

CC

I

CC

1

4

A1642

VCC

GND

V

SUPPLY

1

4

I

CC

R

SENSE

R

SENSE

V+

V+

I+

N

N

S

S

Representative

Differential

Magnetic Profile

Target

Ring Magnet

Sensor Electrical