AS5040 datasheet(3/28 Pages) AMSCO

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AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.6, 03-Oct-06

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Page 3 of 28

Pin 8 (Prog) is also used to program the different

incremental interface modes, the incremental resolution

and the zero position into the OTP (see page 11).

This pin is also used as digital input to shift serial data

through the device in Daisy Chain configuration,

(see page 5).

Pin 11 Chip Select (CSn; active low) selects a device

within a network of AS5040 encoders and initiates serial

data transfer. A logic high at CSn puts the data output

pin (DO) to tri-state and terminates serial data transfer.

This pin is also used for alignment mode (page 13) and

programming mode (page 9).

Pin 12 allows a single wire output of the 10-bit absolute

position value. The value is encoded into a pulse width

modulated signal with 1µs pulse width per step (1µs to

1024µs over a full turn). By using an external low pass

filter, the digital PWM signal is converted into an analog

voltage, allowing a direct replacement of potentiometers.

Functional Description

The AS5040 is manufactured in a CMOS standard

process and uses a spinning current Hall technology for

sensing the magnetic field distribution across the surface

of the chip.

The integrated Hall elements are placed around the

center of the device and deliver a voltage representation

of the magnetic field at the surface of the IC.

Through Sigma-Delta Analog / Digital Conversion and

Digital Signal-Processing (DSP) algorithms, the AS5040

provides accurate high-resolution absolute angular

position information. For this purpose a Coordinate

Rotation Digital Computer (CORDIC) calculates the angle

and the magnitude of the Hall array signals.

The DSP is also used to provide digital information at the

outputs

MagI NCn

and

M agDECn

that

indicate

movements of the used magnet towards or away from the

device’s surface.

A small low cost diametrically magnetized (two-pole)

standard

magnet

provides

the

angular

position

information (see Figure 19).

The AS5040 senses the orientation of the magnetic field

and calculates a 10-bit binary code. This code can be

accessed via a Synchronous Serial Interface (SSI). In

addition, an absolute angular representation is given by a

Pulse Width Modulated signal at pin 12 (PWM).

Besides the absolute angular position information the

device simultaneously provides incremental output

signals. The various incremental output modes can be

selected by programming the OTP mode register bits

(see page 11). As long as no programming voltage is

applied to pin Prog, the new setting may be overwritten

at any time and will be reset to default when power is

turned off. To make the setting permanent, the OTP

default setting is a quadrature A/B mode including the

Index signal with a pulse width of 1 LSB. The Index

signal is logic high at the user programmable zero

position.

The AS5040 is tolerant to magnet misalignment and

magnetic stray fields due to differential measurement

technique and Hall sensor conditioning circuitry.

DSP

Hall Array

Frontend

Amplifier

OTP

Programming

Parameters

Absolute

Interface

(SSI)

Incremental

Interface

Sin

Cos

Ang

Mag

MagINCn

MagDECn

PWM_LSB

CLK

A_LSB_U

B_Dir_V

Index_W

Prog

CSn

PWM

Interface

VDD5V

VDDV3V

LDO 3.3V

Figure 3: AS5040 block diagram

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