DRV10975 Datasheet, PDF (29/57 Pages) Texas Instruments – 12-V, Three-Phase, Sensorless BLDC Motor Driver

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DRV10975
SLVSCP2 – JANUARY 2015
Table 5. Configuring Commutation Advance Timing by Adjusting t_SETTING (continued)
t_SETTING (µs)
TCtrlAdv
[6:0]
HEX
t_SETTING (µs)
TCtrlAdv
[6:0]
HEX
t_SETTING (µs)
TCtrlAdv
[6:0]
HEX
55
0011011
1B
480
1001100
4C
4160
1111101
7D
60
0011100
1C
520
1001101
4D
4480
1111110
7E
65
0011101
1D
560
1001110
4E
4800
1111111
7F
70
0011110
1E
600
1001111
4F
75
0011111
1F
640
1011000
58
80
0101000
28
720
1011001
59
9.4.6 Current Limit
The DRV10975 has several current limit modes to help ensure optimal control of the motor and to ensure safe
operation. The various current limit modes are listed in Table 6. Acceleration current limit is used to provide a
means of controlling the amount of current delivered to the motor. This is useful when the system needs to limit
the amount of current pulled from the power supply during motor start-up. The lock detection current limit is a
configurable threshold that can be used to limit the current applied to the motor. Overcurrent protection is used to
protect the device; therefore, it cannot be disabled or configured to a different threshold. The current limit modes
are described in the following sections.
Current Limit Mode
Acceleration current limit
Lock detection current limit
Overcurrent shutdown
Table 6. DRV10975 Current Limit Modes
Situation
Motor start
Motor locked
Short circuit
Action
Limit the output voltage amplitude
Stop driving the motor and enter lock state
Stop driving and recover when OC signal disappeared
Fault Diagnose
No fault
Mechanical rotation error
Circuit connection
9.4.6.1 Acceleration Current Limit
The acceleration current limit limits the voltage applied to the motor to prevent the current from exceeding the
programmed threshold. The acceleration current limit threshold is configured by writing the SWiLimitThr[3:0] bits
to select I_LIMIT. The acceleration current limit does not use a direct measurement of current. It uses the
programmed motor resistance, Rm, and programmed motor velocity constant, Kt, to limit the voltage applied to
the motor, U, as shown in Figure 25 and Equation 6.
When the acceleration current limit is active, it does not stop the motor from spinning nor does it trigger a fault.
The acceleration current limit function is only available in closed loop control.
Rm
U_LIMIT
I_LIMIT
M BEMF = Kt ´ speed
Figure 25. Acceleration Current Limit
U_LIMIT = I_LIMIT × Rm + Speed × Kt
(6)
9.4.7 Lock Detect and Fault Handling
The DRV10975 provides several options for determining if the motor becomes locked as a result of some
external torque. Five lock detect schemes work together to ensure the lock condition is detected quickly and
reliably. Figure 26 shows the logic which integrates the various lock detect schemes. When a lock condition is
detected, the DRV10975 device takes action to prevent continuously driving the motor in order to prevent
damage to the system or the motor.
In addition to detecting if there is a locked motor condition, the DRV10975 also identifies and takes action if there
is no motor connected to the system.
Copyright © 2015, Texas Instruments Incorporated
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