AS5045 datasheet(22/24 Pages) AMSCO

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AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.5

www.austriamicrosystems.com

Page 22 of 24

14.5

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 400µs (typ.)

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 (see

above).

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 (see section 6):

() 1

4097 −

⋅

off

Position

14.6

Temperature

14.6.1

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:

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 AS5045 can compensate for this temperature related

field strength change automatically, no user adjustment

is required.

14.7

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.

14.7.1

Timing Tolerance over Temperature

The internal RC oscillator is factory trimmed to

±5%.

Over temperature, this tolerance may increase to

±10%.

Generally, the timing tolerance has no influence in the

accuracy or resolution of the system, as it is used mainly

for internal clock generation.

The only concern to the user is the width of the PWM

output pulse, which relates directly to the timing

tolerance of the internal oscillator. This influence

however can be cancelled by measuring the complete

PWM duty cycle instead of just the PWM pulse (see

14.5).

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