Datasheet

1
2
3
4
Neutral
At VDC/2
5
6
off
i=0
A
C
B
off
off
off
on
on
At VDC
At GND
1
2
3
4
Neutral
At VDC/2
5
6
off
i=0
A
C
B
off
off
off
on
on
At VDC
At GND
www.ti.com Appendix A
InstaSPIN-BLDC method requires precise sensing of back-EMF of open-phase of motor to determine the
commutation instant. As shown in Figure 15, for first 0 to 60 degree interval, PWM is applied only to
phase-A top switch and in phase-C bottom switch is continuously ON, back-EMF of open-phase B is rising
and can be measured and integrated to determine the commutation instant. As shown in Figure 16, during
on-time of PWM pulse, with Top switch of phase-A connected to VDC, and bottom switch of phase-C
connected to GND, motor neutral terminal potential rises to VDC/2 with respect to GND and back-EMF of
phase B appears at VDC/2 level above GND. By capturing the absolute value of voltage across phase-B
during PWM on pulse and subtracting it with VDC/2, actual value of motor back-EMF can be derived.
Figure 16. Motor Neutral Voltage During PWM On Period
17
SLVU815–November 2012 InstaSPIN-BLDC Implementation
Submit Documentation Feedback
Copyright © 2012, Texas Instruments Incorporated