DRV10987 Datasheet, PDF (29/69 Pages) Texas Instruments – DRV10987 12- to 24-V, Three-Phase, Sensorless BLDC Motor Driver

www.ti.com
DRV10987
SLVSE89 – AUGUST 2017
8.4.5 Start-Up Current Setting
The start-up current setting is to control the peak start-up current 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 is 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 4 and Figure 21. The duty cycle
applied to the motor is derived from the calculated value for U_Limit and the magnitude of the supply voltage, V_CC,
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 the open-loop acceleration profile of the motor
• Kt is configured by Kt[6:0]
(4)
Rm
U = BEMF + I × Rm
M BEMF = kt × speed
Figure 21. Motor Start-Up Current
8.4.5.1 Start-Up Current Ramp-Up
A fast change in the applied drive current may result in a sudden change in the driving torque. In some
applications, this could result in acoustic noise. To avoid this, the DRV10987 device allows the option of limiting
the rate at which the current is applied to the motor. OpLCurrRt[2:0] sets the maximum voltage ramp-up rate that
is applied to the motor. The waveforms in Figure 22 show how this feature can be used to gradually ramp the
current applied to the motor.
Start Driving With Fast Current Ramp
Start Driving With Slow Current Ramp
Figure 22. Motor Start-Up Current Ramp
8.4.6 Closed Loop
In closed loop operation, the DRV10987 device continuously samples the current in the U phase of the motor
and uses this information to estimate the BEMF voltage that is present. The drive state of the motor is controlled
based on the estimated BEMF voltage.
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: DRV10987
Submit Documentation Feedback
29