DRV10975 Datasheet, PDF (27/57 Pages) Texas Instruments – 12-V, Three-Phase, Sensorless BLDC Motor Driver

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Write to
SpeedCtrl2
DRV10975
SLVSCP2 – JANUARY 2015
SpdCtrl[8]
Write to
SpeedCtrl1
Buffer of
SpdCtrl[8]
SpdCtrl [7:0]
Speed Command
Figure 22. I²C Mode Speed Control
9.4.5.5 Closed Loop Accelerate
To prevent sudden changes in the torque applied to the motor which could result in acoustic noise, the
DRV10975 provides the option of limiting the maximum rate at which the speed command changes.
ClsLpAccel[2:0] can be programmed to set the maximum rate at which the speed command changes (shown in
Figure 23).
y%
Speed command
input
x%
Speed command
after closed loop
accelerate buffer
y%
x%
Closed loop
accelerate settings
Figure 23. Closed Loop Accelerate
9.4.5.6 Control Coefficient
The DRV10975 continuously measures the motor current and uses this information to control the drive state of
the motor when operating in closed loop mode. In applications where noise makes it difficult to control the
commutation optimally, the CtrlCoef[1:0] can be used to attenuate the feedback used for closed loop control. The
loop will be less reactive to the noise on the feedback and provide for a smoother output.
9.4.5.7 Commutation Control Advance Angle
To achieve the best efficiency, it is often desirable to control the drive state of the motor so that the motor’s
phase current is aligned with the motor’s BEMF voltage.
To align the motor’s phase current with the motor’s BEMF voltage, consider the inductive effect of the motor. The
voltage applied to the motor should be applied in advance of the motor’s BEMF voltage (see Figure 24). The
DRV10975 provides configuration bits for controlling the time (t_adv) between the driving voltage and BEMF.
For motors with salient pole structures, aligning the motor BEMF voltage with the motor current may not achieve
the best efficiency. In these applications, the timing advance should be adjusted accordingly. Accomplish this by
operating the system at constant speed and load conditions and by adjusting the t_adv until the minimum current is
achieved.
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