www.austriamicrosystems.com/AS5245

Revision 1.3

28 - 33

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

AS5245 has a built-in interpolator, which ensures that there are no missing pulses at the incremental outputs for rotational speeds of up to

30.000 rpm, even at the highest resolution of 10 bits (512 pulses per revolution).

9.6.4 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).

This error increases linearly with speed:

(EQ 5)

Where:

esampling = angular error [º]

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 processing the data from the AS5245.

9.6.5 Internal Timing Tolerance

The AS5245 does not require an external ceramic resonator or quartz. All internal clock timings for the AS5245 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.

Modulation (PWM) Output on page 17).

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).

Position =

(EQ 6)

9.6.6 Temperature

sensitive to temperature. While linear Hall sensors require a compensation of the magnet’s temperature coefficients, the AS5245 automatically

compensates for the varying magnetic field strength over temperature. The magnet’s temperature drift does not need to be considered, as the

AS5245 operates with magnetic field strengths from ±45…±75mT.

Example:

A NdFeB magnet has a field strength of 75mT @ -40ºC and a temperature coefficient of -0.12% per Kelvin. The temperature change is from -40º

to +125º = 165K.The magnetic field change is: 165 x -0.12% = -19.8%, which corresponds to 75mT at -40ºC and 60mT at 125ºC.

The AS5245 can compensate for this temperature related field strength change automatically, no user adjustment is required.

9.6.7 Accuracy over Temperature

The influence of temperature in the absolute accuracy is very low. While the accuracy is less than or equal to ±0.5º at room temperature, it may

increase to less then or equal to ±0.9º due to increasing noise at high temperatures.

t

on

4097

⋅

t

on

t

off

+

()

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

1

–