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AS5145

Datasheet - Application In form atio n

9.6.5 Internal Timing Tolerance

The AS5145 does not require an external ceramic resonator or quartz. All internal clock timings for the AS5145 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.

internal oscillator. If only the PWM pulse width Ton is used to measure the angle, the resulting value also has this timing tolerance. How-

ulation (PWM) Output on page 17)

Position =

(EQ 6)

9.6.6 Temperature

sensitive to temperature. While linear Hall sensors require a compensation of the magnet’s temperature coefficients, the AS5145 automatically

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

AS5145 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 AS5145 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 can

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

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.

9.7 Differences between AS5145H, AS5145A and AS5145B

Table 15. Functional Differences

Function

AS5145H

AS5145A

AS5145B

Filtering mode

Selectable by customer via

Mode pin (see Table 7)

Pre-defined to Fast mode

Mode_Index pin

Input. Must be set hard wired on PCB

Output

Output

Incremental mode setting

Default disabled. Can be enabled by customer

via programming

Pre-defined to 2x256 ppr

low-jitter (10-bit)

Pre-defined to 2x1024

ppr (12-bit)

Resolution absolute angle

output (PWM and SSI)

12-bit angle

t

on

4097

⋅

t

on

t

off

+

()

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1

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