Design of DC Motor Driver Based on LMD18200 Component
Small electromechanical integration products require that the drive of the DC motor has both a small volume and a large current and voltage output. The Darlington three-stage tube is used to implement the PWM pulse width modulation control. Since the characteristics of the individual components of the discrete device are not the same, the speed regulation performance is not very good, and the circuit cannot achieve high stability. In comparison, the use of the HMD component dedicated to motion control, the LMD18200T, introduced by National Semiconductor (NS) has great benefits. The chip integrates CMOS control circuit and DMOS power device peak output current up to 6A continuous output current up to 3A, working voltage up to 55V also has a temperature alarm and overheating and short circuit protection.
In the non-actuated articulated robot control system, a DC servo motor driver based on the LMD18200 module was developed and applied very well.
2 motion control H-bridge module LMD18200 performance LMD18200% functional block diagram see) is the United States National Semiconductor Corporation, for the motor-driven power integration chip. It consists of four DMOS tubes and its control logic circuit is contained in an 11-pin T-220 package. Its function: rated current 3A peak current 6A; power supply voltage 55V; power transistor on-resistance 0.3n !
; TL and CMOS compatible control signal input 2.1 PWM signal type 1 Type 1 PWM signal contains both direction information and amplitude information, 0 2.2 current sampling and current limit output 1A output current pin 8 output 377nA sampling current.
The resistance between pin 8 and ground converts it into a voltage signal. The linearity and accuracy of this voltage are best when the amplitude is between 5>8V. The maximum voltage at this terminal is 12V. The current sampling circuit does not detect the feedback current and detects only the current in the upper transistor of the bridge arm. The LMD18200 contains a current-limiting protection circuit to detect inrush current in the device. The current quickly closes at 10A when the power device is turned off. After the device is turned off, the protection circuit periodically tries again to turn on the power device. Once the external short-circuit fault disappears, the device resumes normal operation. Since the short circuit will generate a lot of heat, in actual use, the LMD18200 must be equipped with a heat sink with a large enough area and the chip power supply (pin 6) needs 6.45 cm2 of copper foil on the PCB board.
2.3 Charge Pump Circuit As shown, when the high-side DMOS transistor is turned on, the gate voltage of each device should be about 8V higher than the current sampling voltage. This voltage can be obtained using an internal charge pump circuit. The use of the internal 700H: oscillator to charge the internal bootstrap capacitor can obtain 14V voltage, the rise time of the drive voltage is 20nS, which can guarantee the switching frequency of the device to 18H: The external switching capacitor can be used when the switching frequency is higher. The DMOS tube charges the bootstrap capacitor. The 9-bridge output and the bootstrap terminal are connected to a 10nF external capacitor to provide a rise time of up to 10 driving voltages to ensure that the switching frequency reaches 5008H:.
2.4 Internal freewheeling diodes and temperature alarms The four DMOS transistors in the H-bridge have freewheeling (protection) diodes. The reverse recovery time of the high-side freewheeling diode flowing through the 6A reverse current is 70n. The block diagram of the control system At the same time, since the frequency of the PWM signal in the control is up to 15.6 8H, this is relatively high for the opto-isolator device. Ordinary optoelectronics Isolation devices such as the TIL117 cannot be used. The rectangular wave of the PWM signal is input from the optoelectronic isolation device, trapezoidal waves can only be obtained at the output of the opto-isolated device, and accurate PWM control cannot be achieved. Therefore, a high-speed optical isolator 6N177 was selected. The high-speed optocoupler 6N177 is composed of a phosphorous arsenide-based light emitting diode and a photosensitive integrated detection circuit. The signal is received by a photodiode and amplified by an internal high-gain linear amplifier and output by an open collector gate. The high and low transmission delay time of this optoelectronic device is only 48n typical. 4 Conclusion This DC motor driver has been well applied in non-driven articulated robot control systems. Due to the adoption of the LMD18200 power IC, the number of devices used is reduced.
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