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AS5245

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

Figure 18.

Example of Linearity Error Over 360º

9.6.2 Transition Noise

Transition noise is defined as the jitter in the transition between two steps. Due to the nature of the measurement principle (Hall sensors +

Preamplifier + ADC), there is always a certain degree of noise involved. This transition noise voltage results in an angular transition noise at the

outputs. It is specified as 0.06 degrees rms (1 sigma)

= low or open). This is the repeatability of an indicated angle at a given mechanical position. The transition noise has different implications on the

type of output that is used:

Absolute Output; SSI Interface: The transition noise of the absolute output can be reduced by the user by implementing averaging of

readings. An averaging of 4 readings will reduce the transition noise by 6dB or 50%, e.g. from 0.03º rms to 0.015º rms (1 sigma) in slow

mode.

PWM Interface: If the PWM interface is used as an analog output by adding a low pass filter, the transition noise can be reduced by lower-

ing the cutoff frequency of the filter. If the PWM interface is used as a digital interface with a counter at the receiving side, the transition

noise may again be reduced by averaging of readings.

Incremental Mode: In incremental mode, the transition noise influences the period, width and phase shift of the output signals A, B and

Index. However, the algorithm used to generate the incremental outputs guarantees no missing or additional pulses even at high speeds (up

to 30.000 rpm and higher).

9.6.3 High Speed Operation

samples per second. Consequently, the absolute outputs are updated each 384µs (96µs in fast mode). At a stationary position of the magnet,

the sampling rate creates no additional error.

calculated by,

(EQ 3)

(EQ 4)

The upper speed limit in slow mode is ~6.000rpm and ~30.000rpm in fast mode. The only restriction at high speed is that there will be fewer

samples per revolution as the speed increases (see Table 6). Regardless of the rotational speed, the absolute angular value is always sampled

at the highest resolution of 12 bit.

1. Statistically, 1 sigma represents 68.27% of readings; 3 sigma represents 99.73% of readings.

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

1

55

109

163

217

271

325

379

433

487

541

595

649

703

757

811

865

919

973

transition noise

60

rpm

384

()μs

⋅

-----------------------------------

60

rmp 96

μs

⋅

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