DRV10987 Datasheet, PDF (37/69 Pages) Texas Instruments – DRV10987 12- to 24-V, Three-Phase, Sensorless BLDC Motor Driver

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DRV10987
SLVSE89 – AUGUST 2017
8.4.9 Anti-Voltage Surge Function
When a motor is driven, energy is transferred from the power supply into the motor. Some of this energy is
stored in the form of inductive energy or as mechanical energy. The DRV10987 device includes circuits to
prevent this energy from being returned to the power supply, which could result in pumping up the V_CC voltage.
This function is referred to as the AVS and acts to protect the DRV10987 device as well as other circuits that
share the same V_CC connection. Two forms of AVS protection are used to prevent both the mechanical energy
and 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.
8.4.9.1 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 mechanical energy of the motor is returned to the power supply and
the V_CC voltage surges. The mechanical AVS function works to prevent this from happening. The DRV10987
device buffers the speed command value and limits the resulting output voltage, V_{U_MIN}, so that it is not less than
the BEMF voltage of the motor. The BEMF voltage in the mechanical AVS function is determined using the
programmed value for the motor Kt (Kt[6:0]) along with the speed. Figure 35 shows the criteria used by the
mechanical AVS function.
Rm
I_MIN = 0
U
M BEMF
U_MIN = BEMF + I_MIN ´ Rm = BEMF
Figure 35. 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.
• AVSMMd = 1 – AVS mode becomes active when V_CC reaches 24 V. The motor acts as a generator and
returns energy into the power supply until V_CC reaches 24 V. This mode can be used to enable faster
deceleration of the motor in applications where returning energy to the power supply is allowed.
8.4.9.2 Inductive AVS Function
When the DRV10987 device transitions from driving the motor into a high-impedance state, the inductive current
in the motor windings continues to flow and the energy returns to the power supply through the intrinsic body
diodes in the FET output stage (see Figure 36).
S1
S3
S5
V_CC
M
S2
S4
S6
S1
S3
S5
V_CC
M
S2
S4
S6
Driving State
High-Impedance State
Figure 36. Inductive-Mode Voltage Surge
To prevent the inductive energy from being returned to the power supply, the DRV10987 system transitions from
driving to a high-impedance state by first turning off the active high-side drivers, and then after a fixed period of
time (BrkDoneThr[2:0]), turning off the low-side drivers (see Figure 37).
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