Document #: AN120 – CT310 Application Guide Rev0.3

CT310 Application Guide

1 INTRODUCTION

Numerous applications in automotive, industrial and

consumer markets require monitoring of a rotating

mechanical structure. The position sensing of the

angle, speed and direction of motor shafts and

knobs are typical applications for angle sensors.

This application note refers to the CT310 angle

sensor product from Crocus Technology. It provides

guidelines and recommendations to implement the

CT310 in angle sensing or rotation applications.

The two fundamental components of any angle

measurement system are the magnet, including its

relative placement to the sensor, and the angle

sensor, including its intrinsic performance.

Both components will be reviewed in this application

note.

2 CT310 INTRODUCTION

The CT310 refers to the family of angle sensor

products offered by Crocus Technology. Based on

Crocus Technology’s proprietary TMR technology

(MLU

), the CT310 offers inherent advantages

compared to other angle sensing technologies.

2.1 TMR EFFECT

The CT310 makes use of the Tunnel Magneto-

Resistance (TMR) effect that manifests in a change

of electrical resistance of a stack of materials

(including ferromagnetic alloys).

To learn more about TMR technology and its

properties, please refer to AN117.

Figure 1. Representation of a typical TMR junction

including a sense layer, fixed or reference layer and

an external magnet applying a magnetic field to the

sense layer.

The TMR effect is a natural angle sensor. The

resistance of the TMR stack correlates directly with

the angle between the sense layer and the fixed

layer. This allows the CT310 many advantages

compared to other technologies.

• Full 360° rotation discrimination

• Only sensitive to the angle and not the

strength of the external field.

The CT310 borrows similar advantages of

contactless systems:

• Free of mechanical wear and tear

• Safe from dust and contamination

• Independent of mechanical vibration.

Document #: AN120 – CT310 Application Guide Rev0.3

Figure 2. Shows the normalized resistance output of

a TMR junction under rotating external magnetic

field.

2.2 BRIDGE CONFIGURATION

The CT310 features two Wheatstone bridges for X

and Y component detection. Both bridges are on the

same die making the CT310 a monolithic sensor

which improves all the parameters of the sensor,

including:

• Angular error

• Amplitude matching (synchronism)

• Temperature stability.

Figure 3. Typical representation of an angle sensor

including two Wheatstone bridges.

The CT310 makes full use of the MLU technology to

magnetically merge the Cosine (COS) and Sine

(SIN) sensing elements. Thus, pushing the CT310

closer to the perfect “dot” sensor where the COS and

SIN sensing elements see the exact same external

magnetic vector. This will be further described below

in the application note.

2.3 PACKAGE TYPES

Crocus Technology offers the CT310 in two industry

standard packages: an 8-lead TSSOP and a very

low profile, small form factor 8-lead, 2.00 × 2.00 ×

0.45 mm DFN package.

Please refer to the CT310 datasheet for complete

description and specifications of the available

packages.

The small 2.00 × 2.00 × 0.45 mm DFN package

allows for difficult sensor to magnet arrangements,

especially in the case of linear and off-shaft

placements.

3 MECHANICAL DESCRIPTION

3.1 ON-SHAFT

The on-shaft (or end-of-shaft) arrangement is the

most common configuration. A diametral magnet is

mounted on the rotating shaft and the sensor is

placed underneath the magnet. The vertical spacing

between the magnet and top of the sensor package

is referred to as “air gap”.

The CT310 is ideally placed on the center of the

rotating magnet to ensure that during a full 360°

rotation the sensor sees a uniform field. Figure 4

shows an example of the CT310 with the magnet

mounted in an on-shaft position.