DRV10975 Datasheet, PDF (24/57 Pages) Texas Instruments – 12-V, Three-Phase, Sensorless BLDC Motor Driver

DRV10975
SLVSCP2 – JANUARY 2015
Speed
Speed =
A1 ´ t + 0.5 A2 ´ t²
Close loop
Op2ClsThr
www.ti.com
AlignTime
Accelerate Time
Time
Accelerate Time is determined by
Op2ClsThr and A1, A2.
Figure 16. Motor Start-Up Process
Select the first order and second order accelerate rates to allow the motor to reliably accelerate from zero
velocity up to the closed loop threshold in the shortest time possible. Using a slow accelerate rate during the first
order accelerate stage can help improve reliability in applications where it is difficult to accurately initialize the
motor with either align or IPD.
Select the open-to-closed loop threshold to allow the motor to accelerate to a speed that generates sufficient
BEMF for closed loop control. This is determined by the motor’s velocity constant based on the relationship
described in Equation 1.
BEMF = Kt_PH × speed (Hz)
(1)
9.4.4 Start-Up Current Setting
The start-up current setting is to control the peak start-up during open loop. During open loop operation, it is
desirable to control the magnitude of drive current applied to the motor. This is helpful in controlling and
optimizing the rate of acceleration. The limit takes effect during reverse drive, align, and acceleration.
The start current is set by programming the OpenLCurr[1:0] bits. The current should be selected to allow the
motor to reliably accelerate to the handoff threshold. Heavier loads may require a higher current setting, but it
should be noted that the rate of acceleration will be limited by the acceleration rate (StAccel[2:0], StAccel2[2:0]).
If the motor is started with more current than necessary to reliably reach the handoff threshold, it results in higher
power consumption.
The start current is controlled based on the relationship shown in Equation 2 and Figure 17. The duty cycle
applied to the motor is derived from the calculated value for U_Limit and the magnitude of the supply voltage, Vcc,
as well as the drive state of the motor.
U_Limit I_Limit u Rm  Speed Hz u Kt
where
• I_Limit is configured by OpenLCurr[1:0]
• Rm is configured by Rm[6:0]
• Speed is variable based motor’s open loop acceleration profile
• Kt is configured by Kt[6:0]
(2)
Rm
U = BEMF + I × Rm
M BEMF = kt × speed
Figure 17. Motor Start-Up Current
24
Submit Documentation Feedback
Product Folder Links: DRV10975
Copyright © 2015, Texas Instruments Incorporated