DRV10975_15 Datasheet, PDF (32/57 Pages) Texas Instruments – DRV10975 12-V, Three-Phase, Sensorless BLDC Motor Driver

DRV10975
SLVSCP2 – JANUARY 2015
www.ti.com
9.4.7.4 Lock3 (Fault3): No Motor Fault
The phase U current is checked after transitioning from open loop to closed loop. If phase U current is not
greater than 140 mA then the motor is not connected as shown in Figure 31. This condition is treated and
reported as a fault.
DRV10975
M
Figure 31. No Motor Error
9.4.7.5 Lock4: Open Loop Motor Stuck Lock
Lock4 is used to detect locked motor conditions while the motor start sequence is in open loop.
For a successful startup, motor speed should equal to open to closed loop handoff threshold when the motor is
transitioning into closed loop. However, if the motor is locked, the motor speed is not able to match the open loop
drive rate.
If the motor BEMF is not detected for one electrical cycle after the open loop drive rate exceeds the threshold,
then the open loop was unsuccessful as a result of a locked rotor condition.
9.4.7.6 Lock5: Closed Loop Motor Stuck Lock
If the motor suddenly becomes locked, motor speed and Ktc are not able to be refreshed because motor BEMF
zero cross may not appear after the lock. In this condition, lock can also be detected by the following scheme: if
the current commutation period is 2× longer than the previous period.
9.4.8 AVS Function
When a motor is driven, energy is transferred from the power supply into it. Some of this energy is stored in the
form of inductive energy or as mechanical energy. The DRV10975 includes circuits to prevent this energy from
being returned to the power supply which could result in pumping up the VCC voltage. This function is referred to
as the AVS and acts to protect the DRV10975 as well as other circuits that share the same VCC connection.
Two forms of AVS protection are used to prevent both the mechanical energy or the inductive energy from being
returned to the supply. Each of these modes can be independently disabled through the register configuration
bits AVSMEn and AVSIndEn.
9.4.8.1 Mechanical AVS Function
If the speed command suddenly drops such that the BEMF voltage generated by the motor is greater than the
voltage that is applied to the motor, then the motor’s mechanical energy is returned to the power supply and the
VCC voltage surges. The mechanical AVS function works to prevent this from happening. The DRV10975 buffers
the speed command value and limits the resulting output voltage, U_MIN, so that it will not be less than the motor’s
BEMF voltage. The BEMF voltage in the mechanical AVS function is determined using the programmed value for
the motor’s Kt (Kt[6:0]) along with the speed. Figure 32 shows the criteria used by the mechanical AVS function.
Rm
I_MIN = 0
U
M BEMF
U_MIN = BEMF + I_MIN ´ Rm = BEMF
Figure 32. Mechanical AVS
The mechanical AVS function can operate in one of two modes, which can be configured by the register bit
AVSMMd:
AVSMMd = 0 – AVS mode is always active to prevent the applied voltage from being less than the BEMF
voltage.
32
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