DRV10964 Datasheet, PDF (13/27 Pages) Texas Instruments – Three-Phase Sinusoidal Sensorless BLDC Motor Driver

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DRV10964
SLDS227 – MARCH 2016
The DRV10964 includes an anti-voltage-surge (AVS) feature which prevents energy from being transferred from
the motor to the power supply. This feature helps to protect the DRV10964 as well as any other components that
are connected to the power supply (VCC).
7.3.7.1 Protecting Against the Return of Mechanical Energy
Mechanical energy is typically returned to the power supply when the speed command is abruptly decreased. If
the voltage applied to the phase becomes less than the BEMF voltage then the motor will work as a generator
and current will flow from the motor back to VCC. This is illustrated in Figure 12. To prevent this from happening,
the DRV10964 buffers the speed command value and limits the rate at which it is able to change. The AVS
function acts to ensure that the effective output amplitude (U) is maintained to be larger than the BEMF voltage.
This prevents current from becoming less than zero. The value of BEMF used to perform this function is
calculated by the motor Kt and the motor speed.
Rm
U = BEMF + I * Rm
I
M _{BEMF = kt * speed}
If U < BEMF, I<0.
If U > BEMF, I>0.
AVS: U_MIN = BEMF
Figure 12. Mechanical AVS
7.3.7.2 Protecting Against the Return of Inductive Energy
When the DRV10964 suddenly stops driving the motor, the current which is flowing in the motor’s inductance will
continue to flow. It flows through the intrinsic body diodes in the mosfets and charges VCC. An example of this
behavior is illustrated by the two pictures in the top half of Figure 13. When the driver is active, the current flows
from S1 to the motor and then to S6 and is returned to ground. When the driver is placed into a high impedance
(tri-state) mode, the current goes flows from ground through the body diode of S2 to the motor and then through
the body diode of S5 to VCC. The current will continue to flow through the motor’s inductance in this direction
until the inductive energy is dissipated.
Figure 13. Inductive AVS
The lower two pictures in Figure 13 illustrate how the AVS circuit in the DRV10964 device prevents this energy
from being returned to the supply. When the AVS condition is detected the DRV10964 device will act to turn on
the low side device designated as S6. This allows the current flowing in the motor inductance to be returned to
ground instead of being directed to the VCC supply voltage.
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