AS5040 datasheet(16/28 Pages) AMSCO

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AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.6, 03-Oct-06

www.austriamicrosystems.com

Page 16 of 28

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 22).

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.

14 Failure Diagnostics

The AS5040 also offers several diagnostic and failure

detection features:

14.1 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).

14.2 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 finished (within tPwrUp).

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