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AS5045B

Datasheet - Application In form atio n

9.4.2 Magnet Placement

The magnet’s center axis must be aligned within a displacement radius Rd of 0.25mm from the defined center of the IC. The magnet can be

placed below or above the device. The distance can be chosen such that the magnetic field on the die surface is within the specified limits (see

Figure 17). The typical distance “z” between the magnet and the package surface is 0.5mm to 1.5mm, provided the use of the recommended

magnet material and dimensions (6mm x 3mm). Larger distances are possible, as long as the required magnetic field strength stays within the

defined limits.

A magnetic field outside the specified range still can be detected by the chip. But the out-of-range condition will be indicated by MagINCn (pin 1)

and MagDECn (pin 2), (see Table 1).

9.5 Failure Diagnostics

The AS5045B also offers several diagnostic and failure detection features:

9.5.1 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).

9.5.2 Power Supply Failure Detection

By software: If the power supply to the AS5045B 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) must be

added between pin DIO 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 8). 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 AS5045B, the pull-up resistors

(~10k

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.

9.6 Angular Output Tolerances

9.6.1 Accuracy

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 @ 25ºC (see

Figure 19).

Misalignment of the magnet further reduces the accuracy. Figure 18 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 2x2mm (79x79mil) with a

step size of 100µm.

For each misalignment step, the measurement as shown in Figure 19 is repeated and the accuracy

(Errmax – Errmin)/2 (e.g. 0.25º in Figure 19) is entered as the Z-axis in the 3D-graph.