DRV10866_15 Datasheet, PDF (8/22 Pages) Texas Instruments – 5V, 3Phase, Sensorless BLDC Motor Driver

DRV10866
SBVS206A – NOVEMBER 2012 – REVISED MARCH 2015
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7.3 Feature Description
7.3.1 Speed Control
DRV10866 can control motor speed through either the PWM_IN or V_CC pin. Motor speed will increase with higher
PWM_IN duty cycle or V_CC input voltage. The curve of motor speed (RPM) vs PWM_IN duty cycle or V_CC input
voltage is close to linear in most cases. However, motor characteristics will affect the linearity of this speed
curve. DRV10866 can operate at very low V_CC input voltage down to 1.65 V. The PWM_IN pin is pulled up to V_CC
internally and frequency range can vary from 15 kHz to 50 kHz. The motor driver MOSFETs will operate at
constant switching frequency 156 kHz. With this high switching frequency, DRV10866 can eliminate audible
noise and reduce the ripple of V_CC input voltage and current, and thus minimize EMI noise.
7.3.2 Frequency Generator
The FG pin outputs a 50% duty cycle of PWM waveform in the normal operation condition. The frequency of the
FG signal represents the motor speed and phase information. The FG pin is an open-drain output, so an external
pullup resistor is needed when connected to an external system. During the start-up, FG output will stay at high
impedance until the motor speed reaches a certain level and BEMF is detected. During lock protection condition,
FG output will remain high until the motor restarts and start-up process is completed. DRV10866 can output
either FG or ½ FG to indicate motor status with open-drain output through FGS pin selection. When FGS is
pulled to V_CC, the frequency of FG output is half of that when FGS is pulled to GND. Motor speed can be
calculated based on the FG frequency when FGS is pulled to GND, which equals to:
RPM =
(FG ? 60)
pole pairs
where
• FG is in hertz (Hz).
(1)
7.3.3 Lock Protection
If the motor is blocked or stopped by an external force, the lock protection is triggered after lock detection time.
During lock detection time, the circuit monitors the PWM and FG signals. If PWM has an input signal while the
FG output is in high impedance during this period, the lock protection will be enabled and DRV10866 will stop
driving the motor. After lock release time, DRV10866 will resume driving the motor again. If the lock condition still
exists, DRV10866 will proceed with the next lock protection cycle until the lock condition is removed. With this
lock protection, the motor and device will not get over heated or be damaged.
7.3.4 Voltage Surge Protection
The DRV10866 has a unique feature to clamp the V_CC voltage during lock protection and standby mode. If the
lock mode condition is caused by an external force that suddenly stops the motor at a high speed, or the device
goes into standby mode from a high duty cycle, either situation releases the energy in the motor winding into the
input capacitor. When a small input capacitor and anti-reverse diode are used in the system design, the input
voltage of the IC could rise above the absolute voltage rate of the chip. This condition either destroys the device
or reduces the reliability of the device. For this reason, the DRV10866 has a voltage clamp circuit that clamps the
input voltage at 5.95 V, and has a hysteresis of 150 mV. This clamp circuit is only active during the lock
protection cycle or when the device enters standby mode. It is disabled during normal operation.
7.3.5 Overcurrent Protection
The DRV10866 can adjust the overcurrent point through an external resistor connected to the CS pin (pin 9) and
ground. Without this external current sense resistor, the DRV10866 senses the current through the power
MOSFET. Therefore, there is no power loss during the current sensing. The current sense architecture improves
the overall system efficiency. Shorting the CS pin to ground disables the overcurrent protection feature. During
overcurrent protection, the DRV10866 only limits the current to the motor; it does not shut down the device. The
overcurrent limit can be set by the value of current sensing resistor through Equation 2.
I (A) = ³¹²⁰
R_CS (W)
(2)
8
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