AS5040

Data Sheet

www.austriamicrosystems.com

Revision 2.10

29 - 33

Angular Error Caused by Propagation Delay

A rotating magnet will therefore cause an angular error caused by the output delay. This error increases linearly with

speed:

delay

prop

rpm

e

sampling

.

*

6

∗

=

= angular error [°]

rpm

= rotating speed [rpm]

prop.delay

= propagation delay [seconds]

Note: since the propagation delay is known, it can be automatically compensated by the control unit that is processing

the data from the AS5040, thus reducing the angular error caused by speed.

Internal Timing Tolerance

The AS5040 does not require an external ceramic resonator or quartz. All internal clock timings for the AS5040 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 100µs (typ.)

Incremental outputs:

the incremental outputs are updated every

100µs (typ.)

PWM output:

A new angular value is updated every 100µs (typ.).

tolerance.

duty cycle (see section 9):

1025 −

+

⋅

=

off

on

on

t

t

t

Position

Temperature

Magnetic Temperature Coefficient

One of the major benefits of the AS5040 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 coefficient, the AS5040

automatically compensates for the varying magnetic field strength over temperature. The magnet’s temperature drift

does not need to be considered, as the AS5040 operates with magnetic field strengths from

±45…±75mT.

Example:

A 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.

The AS5040 can compensate for this temperature related field strength change automatically, no user adjustment is

required.

Accuracy over Temperature

The influence of temperature in the absolute accuracy is very low. While the accuracy is

≤ ±0.5° at room temperature,

it may increase to

≤±0.9° due to increasing noise at high temperatures.