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Motor driver ICs
3-phase motor driver
BA6871BS
The BA6871BS is a 3-phase, full-wave, pseudo-linear motor driver suited for VCR capstan motors. The IC has a torque ripple cancellation circuit to reduce wow and flutter, and an output transistor saturation prevention circuit that provides superb motor control over a wide range of current. The built-in motor power series regulator allows applications with low power consumption. FApplications 3-phase VCR capstan motors FFeatures 1) 3-phase, full-wave, pseudo-linear driver system. 2) High performance torque ripple cancellation circuit. 3) Reversal braking by detecting the motor direction. 4) Saturation prevention circuit for high- and low-side output transistors. FAbsolute maximum ratings (Ta = 25_C)
5) Motor power supply series regulators. 6) Built-in circuit for output-to-GND short-circuit detection. 7) Two FG amplifiers. 8) Available in a SDIP 32-pin power shrink package.
FRecommended operating conditions (Ta = 25_C)
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Motor driver ICs
FBlock diagram
BA6871BS
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Motor driver ICs
FPin descriptions
BA6871BS
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Motor driver ICs
FInput / output circuits (1) Driver output
BA6871BS
(2)
Hall input
(3)
ED / S
(4)
Torque control input
(5)
Torque limit and current sensing
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Motor driver ICs
BA6871BS
(6)
Series regulator
(7)
Amplifier I / O
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Motor driver ICs
BA6871BS
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC1 = 5V, VM = VCC2 = 12V, AMP*VCC = 12V)
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Motor driver ICs
FCircuit operation (1) Pseudo-linear output and torque ripple cancellation The IC generates a trapezoidal (pseudo-linear) output current, whose waveform phase is 30 degrees ahead of that of the Hall input voltage (Fig. 8).
BA6871BS
The trapezoidal waveform of output current would create intermittence in the magnetic field generated by the 3-phase motor, and would result in an irregular rotation of the motor. To prevent this, the output waveform is obtained by superimposing a triangular wave on the trapezoidal wave (Fig. 9). This process is called torque ripple cancellation.
These pins are the inputs to a differential amplifier. A reference voltage between 2.3 X 3.0V (2.5V recommended) is applied to pin 10. A brake is applied to the motor as described in the following. When the motor is running, pin 11 is given a negative potential with respect to the reference potential. If the pin 11 potential becomes positive, the IC detects the rise of pin 11 potential above the reference potential and activates the motor direction detecting circuit. The motor direction detecting circuit sends a signal to the motor direction setting circuit to reverse the motor direction. This causes a braking torque that depends on the pin 11 potential, so that the motor quickly reduces its speed. At the same time, the positive pin 11 potential is shifted to the reference potential, so that the motor stops smoothly. (3) Output current sensing and torque limitation Pin 31 is the ground pin for the output stage. To sense the output current, a resistor (0.5 recommended) is connected between pin 31 and the ground. The output current is sensed by applying the voltage developed across this resistor to pin 13 as a feedback. The output current can be limited by adjusting the voltage applied to pin 12. The current is limited when pin 12 reaches the same potential as pin 13. The output current (IMAX.) under this condition is given by: V12P*(TL*CSofs) IMAX. = R31P where R31P is the value of the resistor connected between pin 31 and the ground, V12P is the voltage applied to pin 12, and (TL*CSofs) is the offset between the TL and CS pins.
(2) Torque control and reversal brake The output current can be controlled by adjusting the voltage applied to the torque control pins (pins 10 and 11).
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Motor driver ICs
BA6871BS
(4) Motor direction control (pin 29) The motor mode is: Forward when the pin 29 voltage is less than 0.9V, Stop when the voltage is between 1.3 X 3.0V, Reverse when the voltage is above 3.5V. In the stop mode, high- and low-side output transistors are turned off, resulting in a high impedance state. (5) Output transistor saturation prevention circuit This circuit monitors the output voltage and maintain the operation of the output transistors below their saturation levels. Operating the transistors in the linear characteristic range provides good control over a wide range of current and good torque characteristics even during overloading.
As shown in Fig. 14, the regulator circuit reduces the power consumed by the IC by reducing the collector-toemitter (C-E) voltage of the driver transistors. Nearly all the power dissipated by the IC is dissipated between the collectors and emitters of the output transistors. More power is consumed as the C-E voltage increases and as the output current increases. The output transistor C-E voltage is equal to the difference between the supply voltage and the voltage applied to the motor. Because the voltage across the motor decreases with decreasing drive current, the C-E voltage must increase if the supply voltage is fixed. Therefore, to improve the efficiency of the driver and to prevent the power rating of the IC being exceeded, the supply voltage must be varied in response to changes in the output current. The supply voltage is decreased at low current and increased at high current so that no excessive voltage is applied between the transistor collectors and emitters. (7) Output-to-ground short-circuit detection The motor output pins of the IC may be short-circuited to the ground by some fault conditions. A short-circuited output can destroy the output transistors because of excessive current, excessive voltage, or both. Even when a short-circuit condition does not completely destroy the device, it can still cause extreme overheating. To prevent this, the BA6871BS contains a short-circuit detection circuit that turns off the motor drive current if the output-toground potential becomes abnormally low.
(6) Series regulator The BA6871BS has a series regulator output pin. The IC outputs a sink current according to the HIGH level output voltage detected.
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Motor driver ICs
FApplication example
BA6871BS
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Motor driver ICs
FOperation notes The BA6871BS has two thermal shutdown circuits (TSD1 and TSD2) to protect the IC. The typical shutdown temperatures are 175_C for TSD1 and 215_C for TSD 2. When the TSD1 is activated at an elevated chip temperature, the output pins (pins 1, 3, and 30) are set to the open state. TSD1 is functional against excessive power dissipation, output short-circuiting, and other irregularities in the output current, but does not work against overheating caused by high internal currents due to externally caused IC damage or pin-to-pin short-circuiting. When TSD2 is activated at a higher chip temperature, the high- and low-side output transistors are turned on, and the internal resistance between the motor power supply FElectrical characteristic curves
BA6871BS
pin (pin 2) and the output ground pin (31 pin) drops to less than 3. The motor power supply current (IM) is then given by VM [V] IM = RM)R31P)3 [] where IM is the motor supply current VM is the motor supply voltage, RM is the motor power supply output resistance, R31P is the pin-31 resistance. In your application, make sure to connect between the motor power supply and pin 2 a circuit breaker that operates at currents less than IM.
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Motor driver ICs
BA6871BS
FExternal dimensions (Units: mm)
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