AS5045-ASST datasheet(35/47 Pages) AMSCO

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[v2-01] 2017-Jul-13

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AS5045 − Detailed Description

Angular Error Caused by Propagation Delay: A rotating

magnet will cause an angular error caused by the output

propagation delay.

This error increases linearly with speed:

Where:

esampling = angular error [°]

rpm = rotating speed [rpm]

prop.delay = propagation delay [seconds]

Note(s): Since the propagation delay is known, it can be

automatically compensated by the control unit processing the

data from the AS5045.

Internal Timing Tolerance

The AS5045 does not require an external ceramic resonator or

quartz. All internal clock timings for the AS5045 are generated

by an on-chip RC oscillator. This oscillator is factory trimmed to

±5% accuracy at room temperature (±10% over full temperature

range). This tolerance influences the ADC sampling rate and the

pulse width of the PWM output.

• Absolute Output; SSI Interface: A new angular value is

updated every 96μs (typ.) in fast mode and every 384μs

(typ.) in slow mode.

•PWM Output: A new angular value is updated every 400μs

(typ.). The PWM pulse timings Ton and Toff also have the

same tolerance as the internal oscillator. If only the PWM

pulse width Ton is used to measure the angle, the resulting

value also has this timing tolerance. However, this

tolerance can be cancelled by measuring both Ton and Toff

and calculating the angle from the duty cycle.

Temperature

Magnetic Temperature Coefficient: One of the major benefits

of the AS5045 compared to linear Hall sensors is that it is much

less sensitive to temperature. While linear Hall sensors require

a compensation of the magnet’s temperature coefficients, the

AS5045 automatically compensates for the varying magnetic

field strength over temperature. The magnet’s temperature

drift does not need to be considered, as the AS5045 operates

with magnetic field strengths from

±45…±75mT.

Example:

An NdFeB magnet has a field strength of 75mT @ -40°C and a

temperature coefficient of -0.12% per Kelvin. The temperature

change is from -40° to 125° = 165K. The magnetic field change

is: 165 x -0.12% = -19.8%, which corresponds to 75mT at -40°C

and 60mT at 125°C.

(EQ5)

delay

prop

rpm

sampling

∗

(EQ6)

() 1

4097 −

⋅

off

Position

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