AS5040 datasheet(8/28 Pages) AMSCO

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AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.6, 03-Oct-06

www.austriamicrosystems.com

Page 8 of 28

Parameter

Symbol

Typ

Unit

Note

PWM

frequency

fPWM

0.9756 kHz Signal period: 1025µs

MIN pulse

width

PWMIN

µs

- Position 0d

- Angle 0 deg

MAX pulse

width

PWMAX

1024

µs

- Position 1023d

- Angle 359,65 deg

Table 5: PWM signal parameters

Analog Output

An analog output may be generated by averaging the

PWM signal, using an external active or passive lowpass

filter. The analog output voltage is proportional to the

angle: 0°= 0V; 360° = VDD5V.

Using this method, the AS5040 can be used as direct

replacement of potentiometers.

Figure 10: Simple passive 2nd order lowpass filter

R1,R2

≥ 4k7

C1,C2

≥ 1µF / 6V

R1 should be

≥4k7 to avoid loading of the PWM output.

Larger values of Rx and Cx will provide better filtering

and less ripple, but will also slow down the response

time.

Brushless DC Motor Commutation

Mode

Brushless DC motors require angular information for

stator commutation. The AS5040 provides U-V-W

commutation signals for one and two pole pair motors. In

addition to the three-phase output signals, the step (LSB)

output

allows

high

accuracy

speed

measurement. Two resolutions (9 or 10 bit) can be

selected by programming Div0 according to Table 6.

Mode 3.0 (3.1) is used for brush-less DC motors with

one-pole pair rotors. The three phases (U, V, W) are 120

degrees apart, each phase is 180 degrees on and 180

degrees off.

Mode 3.2 (3.3) is used for motors with two pole pairs

requiring a higher pulse count to ensure a proper current

commutation. In this case the pulse width is 256 positions,

equal to 90 degrees.

The precise physical angle at which the U, V and W signals

change state (“Angle” in Figure 11 and Figure 12) is

calculated by multiplying each transition position by the

angular value of 1 count:

Angle [deg] = Position x (360 degree / 1024)

Commutation - Mode 3.0 (One-pole-pair)

Position:

171

341

512

683

853

Angle:

0.0

60.12

119.88

180.0

240.12

299.88

360.0

Width: 512 Steps

CW Direction

Figure 11: U, V and V-signals for BLDC motor commutation (Div1=0, Div0=0)

360°

analog out

Pin12

PWM

Pin7

VSS

0°

VDD

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