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BA6438 Folha de dados(PDF) 4 Page - Rohm |
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BA6438 Folha de dados(HTML) 4 Page - Rohm |
4 / 8 page BA6438S Motor driver ICs !Circuit 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. 1). . 30 ° Hall input Output current Fig. 1 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 ob- tained by superimposing a triangular wave on the trape- zoidal wave (Fig. 2). This process is called torque ripple cancellation. Fig. 2 (2) Torque control and reversal brake The output current can be controlled by adjusting the voltage applied to the torque control pins (pins 16 and 17). These pins are the inputs to a differential amplifier. A ref- erence voltage between 2.3 ~ 3.0V (2.5V recommended) is applied to pin 16. 0 Output current Offset Pin 16 reference voltage (2.5 V) Pin 17 voltage Dead zone (100 mV typically) Fig. 3 A brake is applied to the motor as described in the following.When the motor is running, pin 17 is given a negative potential with respect to the reference potential. If the pin 17 potential becomes positive, the IC detects the rise of pin 17 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 direc- tion. This causes a braking torque that depends on the pin 17 potential, so that the motor quickly reduces its speed. At the same time, the positive pin 17 potential is shifted to the reference potential, so that the motor stops smoothly. (3) Output current sensing and torque limitation Pin 2 is the ground pin for the output stage. To sense the output current, a resistor (0.5 Ω recommended) is con- nected between pin 2 and the ground. The output current is sensed by applying the voltage developed across this resistor to pin 22 as a feedback. The output current can be limited by adjusting the voltage applied to pin 20. The current is limited when pin 20 reaches the same potential as pin 22. The output current (IMAX. ) under this condition is given by: IMAX. = V20P(TL −CSofs) R2P where R2P is the value of the resistor connected between pin 2 and the ground, V20P is the voltage applied to pin 20, and (TL–CSofs ) is the offset between the TL and CS pins. 24pin 1pin 3pin 23pin ATC 2pin VM Fig.4 Output circuit |
Nº de peça semelhante - BA6438 |
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Descrição semelhante - BA6438 |
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