www.austriamicrosystems.com/AS5140H

Revision 1.4

18 - 37

AS5140H

Data Sheet - D e t a i l e d D e s c r i p t i o n

7.5 Brushless DC Motor Commutation Mode

Brushless DC motors require angular information for stator commutation. The AS5140H 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 at pin 12 allows high accuracy speed measurement. Two

resolutions (9 or 10 bit) can be selected by programming Div0 according to Table 20.

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 12

and Figure 13) is calculated by multiplying each transition position by the angular value of 1 count:

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

(EQ 4)

Figure 12. U, V and V-Signals for BLDC Motor Commutation (Div1=0, Div0=0)

Figure 13. U, V and W-Signals for 2Pole BLDC Motor Commutation (Div1=1, Div0=0)

Width : 512 Steps

Width : 512 Steps

CW Direction

W

V

U

0

171

341

512

683

853

0

0.0

60.12

119.88

180.0

240.12

299.88

360.0

Position:

Angle:

Commutation - Mode 3.0

(One-pole-pair)

Width : 256 Steps

Width : 256 Steps

CW Direction

W

V

U

0

171

341

512

683

853

0

0.0

60.12

119.88

180.0

240.12

299.88

360.0

Position:

Angle:

Commutation - Mode 3.2

(Two-pole-pairs)

939

768

597

427

256

85

90.0

150.12

209.88

270.00

330.12

29.88