Many devices currently require the control of multiple motors, which naturally increases the development difficulty during the design and development process, and this difficulty increases with the number of controlled axes. The TMC428 is a 3-axis stepper motor control chip developed by TRINAMIC. It can reduce the amount of peripheral circuitry, reduce the workload of motor control software design, lower development costs, and shorten research and development time.
The TMC428 possesses all the motion control functions required by the system. It serves as the core for controlling and driving three TMC2X6 or TMC2X9 (the company's driver chips) to form a 3-axis stepper system. This control system boasts advantages such as small size, simple structure, and the ability to form a virtual closed loop internally. The I/O section can be implemented by its host microcontroller.
1. Main performance
The TMC428 is a small, cost-effective two-phase stepper motor control chip. It features two independent SPI ports, which can be connected to a microprocessor and a stepper motor driver with an SPI interface to form a complete system. Control commands can be given by the microprocessor via the SPI interface. The TMC428 provides all the functions related to digital motion control, including position control, speed control, and microstepping control—common control functions for stepper motors. If these functions were performed by the microprocessor, they would consume significant system resources. Therefore, using the TMC428 frees up the microprocessor, allowing resources to be used for interface expansion and higher-level control of the stepper motor. In addition, the TMC236 is also a stepper motor driver with a serial interface developed by TRINAMIC. A daisy-chain structure of three TMC236s is a serial communication-based network structure that allows multiple devices with serial communication interfaces to relay data. The TMC428 can connect to these devices via the SPI interface to simultaneously control three two-phase stepper motors.
The main features of TMC428 are as follows :
● It can control up to 3 axes of 2-phase stepper motors, and each axis can operate independently.
● It communicates with microcontroller chips and driver chips via simple SPI, making it easy to use and facilitate the construction of a virtual closed-loop network. The controller can monitor the status of the driver at all times.
● Contains a 24-bit position counter
●Based on the motor motion parameters (position, speed, acceleration) given by the microprocessor, the drive pulse waveform and sequence are generated by lines according to a trapezoidal or triangular velocity pattern to control the position and speed of the motor. Motor parameters such as speed, acceleration, and target position can be changed during motor operation.
● Microstep control is available. 6-bit microstepping resolution allows for settings of 64, 32, 16, 8, 4, 2, and 1. Each motor can be individually selected with its desired microstepping resolution. The maximum full-step frequency is 20kHz.
Programmable current proportional control allows the motor to use different operating currents under different operating conditions.
3. Internal structure and working principle
The internal structure of the TMC428 is shown in Figure 3. The TMC428 consists of registers and on-chip RAM of various units. Internally, it includes two external serial interfaces, a waveform generator and a pulse generator, a microstepping unit, a multi-port RAM controller, and an interrupt controller.
The TMC428 typically obtains control instructions from a microprocessor, which in turn reads and writes to the TMC428's registers and RAM by sending and receiving fixed-length data packets. The TMC428's registers and on-chip RAM have different functions. Registers store overall motor configuration parameters and motion parameters, while the on-chip RAM stores the configuration of the drive serial interface and the microstepping table. Overall motor parameters refer to the configuration of the TMC236 in the driver daisy chain. Motion parameters include the current position, target position, maximum speed, maximum acceleration, current ratio, waveform generator and pulse generator parameters, and microstepping resolution for each motor. The on-chip RAM includes a 64-address data space, with each address storing 24 bits of data. The first 32 bits are the configuration of the driver daisy chain serial communication data packets, and the last 32 bits are the microstepping table.
After initialization, the TMC428 can automatically send data packets to each TMC2X6 or TMC2X9 driver chip in the daisy chain. This means the driver serial interface can operate automatically after initialization without microprocessor intervention. Motor control is achieved simply by writing the position and speed into the designated registers. The TMC428's multi-port RAM controller manages the data access timing. This allows the microprocessor to read and write data from registers and on-chip RAM at any time.
The waveform generator processes the motion parameters stored in the registers and calculates the motor speed curve. The pulse generator then generates step pulses based on the speed calculated by the waveform generator. When step pulses are generated, the TMC428's driver serial interface automatically sends data packets to the stepper motor driver daisy chain to drive the stepper motor. When microstepping control is used, the microstepping unit begins processing the step pulses generated by the pulse generator, and simultaneously generates full-step, half-step, and microstep pulses according to the selected microstepping resolution, sending them to the driver daisy chain via the driver serial port.
The driver serial interface is the communication interface between the TMC428 and the driver daisy chain. The length of the serial data packets between the TMC428 and the driver is configurable to accommodate SPI ring structures composed of circuits of different types and manufacturers, with a maximum data length of 64 bits. After initialization, communication between the TMC428 and the stepper motor driver is completed automatically. Different types of drivers with SPI interfaces can be mixed and matched to form a daisy chain structure and connect to the TMC428.
After initialization, the TMC428 can automatically send data packets to each TMC2X6 or TMC2X9 driver chip in the daisy chain. This means the driver serial interface can operate automatically after initialization without microprocessor intervention. Motor control is achieved simply by writing the position and speed into the designated registers. The TMC428's multi-port RAM controller manages the data access timing. This allows the microprocessor to read and write data from registers and on-chip RAM at any time.
The waveform generator processes the motion parameters stored in the registers and calculates the motor speed curve. The pulse generator then generates step pulses based on the speed calculated by the waveform generator. When step pulses are generated, the TMC428's driver serial interface automatically sends data packets to the stepper motor driver daisy chain to drive the stepper motor. When microstepping control is used, the microstepping unit begins processing the step pulses generated by the pulse generator, and simultaneously generates full-step, half-step, and microstep pulses according to the selected microstepping resolution, sending them to the driver daisy chain via the driver serial port.
The driver serial interface is the communication interface between the TMC428 and the driver daisy chain. The length of the serial data packets between the TMC428 and the driver is configurable to accommodate SPI ring structures composed of circuits of different types and manufacturers, with a maximum data length of 64 bits. After initialization, communication between the TMC428 and the stepper motor driver is completed automatically. Different types of drivers with SPI interfaces can be mixed and matched to form a daisy chain structure and connect to the TMC428.
4. Application
4.1 Compatibility
The TMC428 is compatible with stepper motor driver circuits from most manufacturers. It can be directly connected to stepper motor drivers with SPI ports, or connected to common parallel port drivers via additional components. Even stepper motor drivers with step and direction inputs can be controlled by the TMC428. Connecting the TMC2X6 or TMC2X9 stepper motor driver chips in a simple serial daisy-chain configuration and using the TMC428 to construct a 3-axis stepper motor control system allows for better utilization of the TMC428's capabilities.
4.2 Status Detection
Real-time monitoring of motor operating status is crucial for the safety and control of the entire system, and the TMC428 provides status detection functionality. Each time the processor sends a data packet to the TMC428, the TMC428 returns data to the microprocessor. Most motor drive circuits with serial ports provide different status bits (operating, inactive, etc.) and error flags (short circuit, open circuit, overheating, etc.). This allows the TMC428 to provide the current motor motion parameters, operating mode, and status bits at any time. The data packet returned to the TMC428 from the motor drive daisy chain is 48 bits long. The TMC428 stores this data in two 24-bit registers. The microprocessor can then directly read the information in these registers, such as detecting motor position, speed, acceleration, and even current parameters during motor operation.
5. System Composition
The system uses RAM or a simple, inexpensive microcontroller as its microprocessor, combined with a TMC428 and driver chips TMC2X6 (TMC236, 239) or TMC2X9 (TMC239, 249) to control and drive a 3-axis stepper motor. The TMC236 and TMC246 integrate a dual-bridge driver circuit composed of HVC MOSFETs, using a constant current chopper drive method to drive the bipolar two-phase stepper motor, offering advantages such as low power consumption and high efficiency. The entire system is shown in Figure 4.
As shown in Figure 4, the system composed of a dedicated stepper motor motion controller and drive circuit has advantages such as simple peripheral circuitry, strong anti-interference capability, and high reliability, reducing the development cost of the control circuit. The entire system has only five ICs besides the power supply, resulting in a small size and simple control, making it particularly suitable for driving 3-axis stepper motors. Experiments have shown that the stepper motor controlled by this driver has high positioning accuracy, good acceleration and deceleration performance, and excellent start-stop and reverse performance. It is widely used in security equipment, instrumentation, office automation, and many other fields.
In addition, to help customers improve the control accuracy of their systems, TRINAMIC has developed the TMC423 encoder processing chip, which can form a three-axis closed-loop control and can receive input from a three-axis incremental encoder.
