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[Abstract] The LMD18200 is a H-bridge assembly that is dedicated to DC motor-driven H-bridge introduced by the National Semiconductor Company (NS). Integrated CMOS control circuits and DMOS power devices on the same chip, using it to form a complete motion control system with the main processor, motor, and incremental encoders. LMD18200 is widely used in printers, robots, and various automation control. This article describes the structure, principle and typical application of the LMD18200 chip.
1, main performance
L peak output current up to 6A, continuous output current 3A;
l The working voltage is up to 55V;
l low rds (on) Typically 0.3W per switch;
l TTL / CMOS compatible input;
l None "shang-through" current;
l has temperature alarms and overheating and short-circuit protection;
l The chip is increased by 145 ° C, and the chip is turned off when the knot temperature reaches 170 ° C;
L has good anti-interference.
2. Typical application
l Drive DC motors, step machine
l Servo mechanism system location and speed
l Applicable to robot control systems
l Applicable to digital control systems
l Applicable to computer printers and plotter
3, internal structure and pin description
The LMD18200 profile structure is shown in Figure 1, and the internal circuit block Figure 2 is shown in the figure. It has 11 pins, using TO-220 and double-column insert packages.
The functions of each pin are as follows:
Be
Pin
name
Function description
1,11
Subload input capacitive connection end of bridge arms 1, 2
At the foot 1 and the foot 2, the foot 10 and the foot 11 should access 10UF from the boiled capacitance
2, 10
H bridge output
Be
3
Direction input
When the steering, the output drive current is shown in Table 1. This pin control output 1 and the direction of current between the output 2 (both pin 2, 10), thereby controlling the direction of the motor rotation.
4
Brake input
When the brake is made, the output drive current is shown in Table 1. The motor winding is shorted to make it brakes through this end. When the brakes, the foot is logically high, and the PWM signal input (pin 5) is set to logic high, and the logic state of the 3 pin is determined to the device used by the short circuit motor. 3 feet are logic high levels, two high-end transistors in the H bridge are turned on; 3 feet are logically low, and two low-end transistors in the H bridge are turned on. The foot 4 is logically high, and the foot 5 is logically low. All transistors in the h bridge turn off, at this time, only small bias streams (1.5mA) per output.
5
PWM signal input
The relationship between the PWM signal and the driving current direction is shown in Table 1. This end is used with 3 feet (direction input), which is determined in the PWM signal type.
6,7
Power terminal and negative end
Be
8
Current sampling output
A current sampling signal is provided, typically 377 μA / a.
9
Temperature alarm output
Temperature alarm output provides temperature alarm signal. When the chip is knocked at 145 ° C, the end becomes low; when the knot temperature reaches 170 ° C, the chip is turned off.
Be
Table 1 LMD18200 Logic Table
Be
PWM
Steering
brake
Actual output drive current
Motor working status
Hide
Hide
L
Exube 1, flow 2
Forward
Hide
L
L
Flowing into 1, out of 2
Reverse
L
×
L
Exube 1, out 2
stop
Hide
Hide
Hide
Exube 1, out 2
stop
Hide
L
Hide
Flowing into 1, flowing into 2
stop
L
X
Hide
None
Be
LMD18200 Working principle:
Internal integrated four DMOS tubes, form a standard H-drive bridge. The gate control voltage is supplied to the two switchgears of the upper bridge arm by the charging pump circuit, and the charging pump circuit is from a 300 kHz operating frequency. The second charging pump circuit can be formed at the pin 1, 11 outer capacitance, the larger the outer capacitance, the faster the capacitance input to the switching pipe gate, the shorter the voltage rises, and the operating frequency can be higher. The pin 2, 10 is connected to the DC electrical armature, and the direction of the current current should be from the lead to pin 10; the direction of the current should be from the pin 10 to the pin 2 during the reverse rotation. The current detecting output pin 8 can be connected to the ground resistance, output overflow through the resistance. The overcurrent threshold of the internal protection circuit is 10A, and the output is automatically blocked when the value is exceeded, and the output is periodically automatically recovered. If the overcurrent duration is longer, the overheating protection will turn off the entire output. The overheating signal can also be output by the pin 9, and the pin 9 has an output signal when the temperature is 145 degrees.
4, typical application
The LMD18200 typical application circuit is shown in Figure 3.
The LMD18200 provides a bipolar drive mode and a single pole drive mode. The bipolar drive means that the voltage polarity of the motor armature is positive and negative in a PWM cycle. Although the bipolar reversible system has the advantages of low speed operation, there is also a shortcoming of current fluctuations, large power loss, and must increase the risk of switching tubes to avoid switching tubes, which limits the improvement of the switching frequency. Therefore, only the control of the medium and small power DC motor. This article will be described in the unipolar reversible drive. The unipolar driving method refers to the motor electrical electrical electromechanical voltage in a PWM cycle.
The application circuit is an example of the Motorola 68332CPU and an LMD18200 interface that forms a unipolar driven DC motor closed-loop control circuit. In this circuit, the PWM control signal is input through the pin 5, while the steering signal is input through the pin 3. Depending on the duty cycle of the PWM control signal to determine the speed and steering of the DC motor. A incremental photoelectric encoder is used to feed back the actual position of the motor, output AB two phases, detect the motor speed and position to form a closed loop position feedback, thereby achieving an accurate control motor.
5, conclude
The digital control of the motor is the development trend of motor control, and the motor is controlled by the microcontroller is the most commonly used means of achieving digital control of motor. Use a special motor control chip LMD18200 to alleviate the load on the microcontroller, and work more reliable.
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