DRV10987 Datasheet, PDF (28/69 Pages) Texas Instruments – DRV10987 12- to 24-V, Three-Phase, Sensorless BLDC Motor Driver

DRV10987
SLVSE89 – AUGUST 2017
www.ti.com
Table 4. Configuration Options for Controlling Open-Loop Motor Start
DESCRIPTION
Open- to closed-loop threshold
Align time
First-order accelerate
Second-order accelerate
Open-loop current setting
Align current setting
Open-loop current ramping
REG. NAME
CONFIG4
CONFIG4
CONFIG4
CONFIG4
CONFIG3
CONFIG3
CONFIGURATION
BITS
Op2ClsThr[4:0]
AlignTime[2:0]
StAccel[2:0]
StAccel2[2:0]
OpenLCurr[1:0]
OpLCurrRt[2:0]
MIN. VALUE
0.8 Hz
40 ms
0.019 Hz/s
0.0026 Hz/s²
200 mA
150 mA
0.023 V_CC/s
MAX. VALUE
204.8 Hz
5.3 s
76 Hz/s
57 Hz/s²
1.6 A
1.2 A
6 V_CC/s
8.4.3.6 Start-Up Timing
Start-up timing is determined by the align and accelerate time. The align time can be set by AlignTime[2:0]. The
accelerate time is defined by the open- to closed-loop threshold Op2ClsThr[4:0] along with the first-order
StAccel[2:0](A1) and second-order StAccel2[2:0](A2) accelerate rates. Figure 20 shows the motor start-up
process.
Speed
Speed =
A1 ´ t + 0.5 A2 ´ t²
Close loop
Op2ClsThr
AlignTime
Accelerate Time
Time
Accelerate Time is determined by
Op2ClsThr and A1, A2.
Figure 20. 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 velocity constant of the motor based on the relationship
described in Equation 2.
BEMF = Kt_PH × speed (Hz)
(2)
8.4.4 Align Current
During the align state, the measured align current is dependent on actual motor resistance and r_DS(on) of the
internal FETs. The relationship between measured align current and configured align current is derived from
actual motor resistance, configured motor resistance and r_DS(on).
AlignCurrent
_
Measured
=
AlignCurrent
_
Configured
´
é
ê
R_m
êë^Rmotor ^{+ r}DS(on)
ù
ú
úû
where
• AlignCurrent_Measured is the actual align current measured during the align state
• AlignCurrent_Configured is the align current configured by OpenLCurr[1:0]
• R_motor is the actual motor resistance
• r_DS(on) is the resistance between the drain and source of the FETs during the on-state
• R_m is configured by Rm[6:0]
(3)
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