AS5043 datasheet(17/26 Pages) AMSCO

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AS5043 Programmable 360° Magnetic Angle Encoder

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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.

17 Failure Diagnostics

The AS5043 also offers several diagnostic and failure

detection features:

17.1 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: Pin #1 (MagRngn) is a logical NAND-ed

combination of the MagInc and MagDec status bits. It is

an open-drain output and will be turned on (= low with

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

of range.

By hardware: Pin #12 (Vout) is the analog output of the

DAC and OP-Amp. The analog output will be 0V, when

the magnetic field is out of range (all analog modes).

17.2 Power supply failure detection

By software: If the power supply to the AS5043 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 MagRngn pin is an open drain output

and requires an external pull-up resistor. In normal

operation, this pin is high ohmic and the output is high.

In a failure case, either when the magnetic field is out of

range or the power supply is missing, this output will

become low. To ensure an adequate low level in case of

a broken power supply to the AS5043, the pull-up

resistor (~10k

Ω) must be connected to the positive

supply at pin 16 (VDD5V).

18 Angular Output tolerances

18.1 Accuracy; digital outputs

Accuracy is defined as the error between measured

angle and actual angle. It is influenced by several

factors:

the non-linearity of the analog-digital converters,

internal gain and mismatch errors,

non-linearity due to misalignment of the magnet

As a sum of all these errors, the accuracy with centered

magnet = (Errmax – Errmin)/2 is specified as better than

±0.5 degrees @ 25°C (see Figure 23).

Misalignment of the magnet further reduces the

accuracy. Figure 22 shows an example of a 3D-graph

displaying non-linearity over XY-misalignment. The

center of the square XY-area corresponds to a centered

magnet (see dot in the center of the graph). The X- and

Y- axis extends to a misalignment of

±1mm in both

directions. The total misalignment area of the graph

covers a square of 2x2 mm (79x79mil) with a step size of

100µm.

For each misalignment step, the measurement as shown

in Figure 23 is repeated and the accuracy

(Errmax – Errmin)/2 (e.g. 0.25° in Figure 23) is entered as

the Z-axis in the 3D-graph.

18.2 Accuracy; analog output

The analog output has the same accuracy as the digital

output with the addition of the nonlinearities of the DAC

and the OPAMP (+/-1LSB; see Table 5 and 19.3.5).

-1000

-700

-400

-100

200

500

800

Linearity Error over XY-misalignment [°]

Figure 22: Example of linearity error over XY misalignment

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