AS5045-ASST datasheet(34/47 Pages) AMSCO

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ams Datasheet

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[v2-01] 2017-Jul-13

AS5045 − Detailed Description

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 0.03°rms to 0.015°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 lowering 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.

High Speed Operation

Sampling Rate: The AS5045 samples the angular value at a rate

of 2.61k (slow mode) or 10.42k (fast mode, selectable by pin

MODE) 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.

Absolute Mode: At a sampling rate of 2.6kHz/10.4kHz, the

number of samples (n) per turn for a magnet rotating at high

speed can be calculated by

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.

Regardless of the rotational speed, the absolute angular value

is always sampled at the highest resolution of 12 bit.

Propagation Delays

The propagation delay is the delay between the time that the

sample is taken until it is converted and available as angular

data. This delay is 96μs in fast mode and 384μs in slow mode.

Using the SSI interface for absolute data transmission, an

additional delay must be considered, caused by the

asynchronous sampling (0 … 1/fsample) and the time it takes the

external control unit to read and process the angular data from

the chip (maximum clock rate = 1MHz, number of bits per

reading = 18).

(EQ3)

rpm

slow

384

mod

⋅

(EQ4)

rpm

fast

mod

⋅

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