AS5045 datasheet(19/24 Pages) AMSCO

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AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.5

www.austriamicrosystems.com

Page 19 of 24

12 Simulation Modeling

Figure 20: Arrangement of Hall sensor array on chip (principle)

With reference to Figure 20, a diametrically magnetized

permanent magnet is placed above or below the surface

of the AS5045. The chip uses an array of Hall sensors to

sample the vertical vector of a magnetic field distributed

across the device package surface. The area of magnetic

sensitivity is a circular locus of 1.1mm radius with

respect to the center of the die. The Hall sensors in the

area of magnetic sensitivity are grouped and configured

such that orthogonally related components of the

magnetic fields are sampled differentially.

The differential signal Y1-Y2 will give a sine vector of

the magnetic field. The differential signal X1-X2 will give

an orthogonally related cosine vector of the magnetic

field.

The angular displacement (

Θ) of the magnetic source

with reference to the Hall sensor array may then be

modelled by:

()

−

arctan

The

±0.5° angular error assumes a magnet optimally

aligned over the center of the die and is a result of gain

mismatch errors of the AS5045. Placement tolerances of

the die within the package are

±0.235mm in X and Y

direction, using a reference point of the edge of pin #1

(see Figure 20)

In order to neglect the influence of external disturbing

magnetic fields, a robust differential sampling and

ratiometric calculation algorithm has been implemented.

The differential sampling of the sine and cosine vectors

removes any common mode error due to DC components

introduced by the magnetic source itself or external

disturbing magnetic fields. A ratiometric division of the

sine and cosine vectors removes the need for an

accurate absolute magnitude of the magnetic field and

thus accurate Z-axis alignment of the magnetic source.

The recommended differential input range of the

magnetic field strength (B(X1-X2), B(Y1-Y2)) is

±75mT at the

surface of the die. In addition to this range, an additional

offset of

±5mT, caused by unwanted external stray fields

is allowed.

The chip will continue to operate, but with degraded

output linearity, if the signal field strength is outside the

recommended range. Too strong magnetic fields will

introduce errors due to saturation effects in the internal

preamplifiers. Too weak magnetic fields will introduce

errors due to noise becoming more dominant.

13 Failure Diagnostics

The AS5045 also offers several diagnostic and failure

detection features:

13.1

Magnetic Field Strength Diagnosis

By software: the MagINC and MagDEC status bits will

both be high when the magnetic field is out of range.

By hardware: Pins #1 (MagINCn) and #2 (MagDECn) are

open-drain outputs and will both be turned on (= low with

external pull-up resistor) when the magnetic field is out

of range. If only one of the outputs are low, the magnet is

either moving towards the chip (MagINCn) or away from

the chip (MagDECn).

13.2

Power Supply Failure Detection

By software: If the power supply to the AS5045 is

interrupted, the digital data read by the SSI will be all

“0”s. Data is only valid, when bit OCF is high, hence a

data stream with all “0”s is invalid. To ensure adequate

low levels in the failure case, a pull-down resistor

(~10k

Ω) should be added between pin DO and VSS at

the receiving side

By hardware: The MagINCn and MagDECn pins are

open drain outputs and require external pull-up resistors.

In normal operation, these pins are high ohmic and the

outputs are high (see Table 5). In a failure case, either

when the magnetic field is out of range of the power

supply is missing, these outputs will become low. To

ensure adequate low levels in case of a broken power

supply to the AS5045, the pull-up resistors (~10k

Ω) from

AS5045 die

Radius of circular Hall sensor

array: 1.1mm radius

Center of die

2.433 mm

±0.235mm

3.9 mm

±0.235mm

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