Self-Calibrating TPOS Speed Sensor IC

Optimized for Automotive Cam Sensing Applications

ATS675LSE

10

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Functional Description

Internal Electronics

This device contains a self-calibrating Hall effect IC that includes

a Hall element, a temperature compensated amplifier, and offset

cancellation circuitry. The IC also contains a voltage regulator

that provides supply noise rejection over the operating voltage

range. The Hall transducers and the electronics are integrated

on the same silicon substrate by a proprietary BiCMOS process.

Changes in temperature do not greatly affect this device, due to

the stable amplifier design and the offset rejection circuitry. The

Hall IC supports a chopper stabilized Hall element that measures

the intensity of magnetic gradients and provides an electrical

signal that represents the target features.

Hall Technology

The ATS675 contains a single-chip Hall effect sensor IC, a 4-pin

leadframe, a specially designed rare-earth pellet, and a ferrous

pole piece (a precisely-mounted magnetic field concentrator).

The Hall IC supports a chopper stabilized Hall element that

measures the magnetic gradient created by the passing of a fer-

romagnetic object. This is illustrated in figure 5. The difference

in the magnetic gradients created by teeth and valleys allows the

devices to generate a digital output signal that is representative of

the target features.

Output Profile Polarity (LT/HT Option)

cal profile of the target, as illustrated in figure 6. The customer

can choose the relative polarity of the output waveform. This

assigns the polarity opposite tooth features (the inverse polarity

low when a tooth is opposite the device, and the HT option sets

ity assignment applies throughout device operation. This ease of

use reduces design time and incremental assembly costs for most

applications.

Automatic Gain Control (AGC)

The Automatic Gain Control (AGC) feature ensures that the

ATS675 initial switching thresholds are isolated from the effects

of changes in the effective air gap (the total distance between

the Hall element and the nearest feature of the target). AGC is

implemented by unique patented self-calibrating circuitry, and

normalizes the sensed magnetic gradient so the internal processed

signal falls within the optimum processing range.

Figure 5. Application cross-section: (A) target tooth opposite device, and

(B) target valley opposite device

Target (Gear)

ATS Device

High-B field

Back-Biasing

Rare-Earth Pellet

Plastic

Hall element

Leadframe

Hall IC

Low-B field

Pole piece

(Concentrator)

North Pole

South Pole

(A)

(B)

inverted (LT option), or in-phase with the target profile (HT option), when

electrically connected as in figure 1.

Target

Mechanical Profile

Processed

Input Signal, V

PROC

Device power-on

0

V+

Target

Magnetic Profile

|B|

0

Output Switch State

HT option

(Following)

On Off On Off On Off On

Off

Output Switch State

LT option

(Inverting)

On Off On Off On Off On Off