AS5040

Data Sheet

www.austriamicrosystems.com

Revision 2.10

25 - 33

The angular displacement (

Θ) of the magnetic source with reference to the Hall sensor array may then be modelled

by:

()

()

°

±

−

−

=

Θ

5

.

0

2

1

2

1

arctan

X

X

Y

Y

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 AS5040. 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 (Figure 23).

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 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.

17 Failure Diagnostics

The AS5040 also offers several diagnostic and failure detection features:

Magnetic Field Strength Diagnosis

By software:

the MagINCn and MagDECn 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 is low, the magnet is either

moving towards the chip (MagINCn) or away from the chip (MagDECn).

Power Supply Failure Detection

By software:

If the power supply to the AS5040 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 3). In a failure case, either when the

magnetic field is out of range or the power supply is missing, these outputs will become low. To ensure adequate low

levels in case of a broken power supply to the AS5040, the pull-up resistors (>10k

Ω) from each pin must be

connected to the positive supply at pin 16 (VDD5V).

By hardware:

PWM output: The PWM output is a constant stream of pulses with 1kHz repetition frequency. In case of

power loss, these pulses are missing.

By hardware:

Incremental outputs: In normal operation, pins A(#3), B(#4) and Index (#6) will never be high at the

same time, as Index is only high when A=B=low. However, after a power-on-reset, if VDD is powered up or restarts

after a power supply interruption, all three outputs will remain in high state until pin CSn is pulled low. If CSn is

already tied to VSS during power-up, the incremental outputs will all be high until the internal offset compensation is