| Brushless DC motor has the advantages of small volume,low noise and high efficiency.It is widely used in industry,aerospace,automobile and other fields.With the continuous development of motor application products in the direction of miniaturization,the use of Brushless DC motor drive chips with lower cost and higher integration has gradually become the mainstream of the market,and the localization of chips has become an inevitable trend,it is of great significance to study the drive chip of Brushless DC motor.In this paper,a PWM control driver chip of Brushless DC motor is designed.Through the analysis of the working principle of Brushless DC motor and the advantages and disadvantages of two different types of H-bridge driver circuits,it is determined to select the H-bridge with high side P transistor as the main driver circuit.By comparing and analyzing the control complexity and loss of the three working modes of H-bridge,it is concluded that the unipolar working mode is more suitable for the drive chip of Brushless DC motor.According to this,the switching transistor driver circuit of H-bridge in unipolar working mode is designed,which is mainly composed of adaptive dead time control circuit,level conversion circuit and high-voltage driver circuit.The adaptive dead time control circuit can automatically adjust the dead time according to the change of switching transistor grid voltage,and the level conversion circuit converts the low-voltage level signal into the high-voltage level signal required by the subsequent high-voltage driver circuit,the high voltage drive circuit uses a current source to charge and discharge the grid of the switch transistor,which can ensure the switching speed of the switch transistor and reduce EMI at the same time.A digital PWM module is designed,which can convert the input PWM speed reference signal within the variation range of given frequency(100Hz～100kHz)and duty cycle(10%～97%)into H-bridge PWM driver signal with constant frequency(30kHz)and the same duty cycle.The method of continuously accumulating and averaging the duty cycle detection value of a single detection cycle is adopted,which not only improves the accuracy of H-bridge PWM driver signal,but also gradually increases its duty cycle after the chip is powered on,The soft start function is realized.In addition,other key circuit modules of the chip are designed,mainly including bandgap reference circuit,LDO circuit,oscillator circuit,over temperature and over voltage protection circuit.Finally,the design of the whole chip is completed.The whole circuit is simulated and analyzed based on X-FAB 0.35um BCD process.The results show that after the chip is powered on,the current in the motor coil gradually increases,which realizes the effect of soft start,and the output meets the expectation under the conditions of different input PWM frequency and duty cycle.Finally,the layout of the whole circuit is designed based on the X-FAB 0.35um BCD process design rule file,and has been verified by DRC,LVS and so on. |
