Abstract: The SPI-7210M is a two-phase stepper/bipolar motor driver IC, applicable to 1- to 2-phase excitation motors with a power supply voltage of 36V (max) and a motor current of ±1.0A. This article details the working principle and design considerations of the SPI-7210M, and provides a performance comparison with the mainstream product UDN2916LB. Keywords: Stepper motor driver, SPI-7210M, UDN2916LB Introduction Stepper motors are digital components, easily interfaced with digital circuits, but the signal energy of general digital circuits is far from sufficient to drive stepper motors. Therefore, a matching driver circuit is necessary to drive the stepper motor. The SPI-7210M introduced in this article is a new generation stepper motor driver product manufactured by SANKEN. Compared with many mainstream products on the market, the SPI-7210M ensures precise control and long-term reliable operation of the stepper motor. The SPI -7210M is a two-phase stepper motor driver that uses a dual-power supply: a primary power supply and a control logic power supply (VBB, 8–30V). The device consists of a base drive circuit (VDD, 3–5.5V), a current control circuit, and an overheat protection PWM circuit. The SPI-7210M requires few external components (two power detection resistors and two power setting resistors) and uses a 16-pin HSOP package. The internal structure and pin functions of the SPI-7210M are shown in the schematic diagram. Table 1 lists its pin functions. The internal power control circuit supplies power to the VBB terminal, with a voltage range of 8–30V. Its TSD (overheat protection) circuit forces the chip to stop operating when the chip temperature exceeds 160°C, ensuring product lifespan. Therefore, the design should ensure that the chip's operating temperature is below 160°C; otherwise, the product lifespan will be drastically shortened. The input circuit of the motor control signal can control the logic level of the OutA and OutB outputs through the logic Ph of the control terminal. When the Ph signal is low, the current from OUTB flows into OUTA; when Ph is high, the current flows from OUTA into OUTB. Its control logic truth table is shown in Table 2. The function of the motor PWM current control circuit is to compare the reference voltage (V[sub]REF[/sub]) input through the REF terminal and the voltage (V[sub]SENSE[/sub]) at the SENSE terminal, and output a PWM control signal to the pre-drive circuit (Logic & PRI-Drive) to control the output current. Application Design Example The EPSON MU-110 printer chip, which is widely used in ECR, POS, and tax-controlled cash registers, is shown in Figure 2. Figure 2 shows an application circuit using SPI-7210M to drive the motor. The current parameters of the paper feed motor in the printer core are as follows: Acceleration/deceleration drive current: 300±21 mA (2-phase excitation) Constant speed drive current: 300±21 mA (2-phase excitation) Holding current: 90±20 mA (2-phase excitation) From the above parameters, it can be seen that the motor drive current ITRIPMAX required for this circuit is 300 mA; if the selected parameters are VDO resistor 5V, R1 7 kΩ1, R2 3kΩ, RS 1kΩ2, then: VREF = VDOR2/(R1+R2) = 1.5VITRIPMAX = VREF /(5R[sub]s[/sub])=300mA In the specific design, during acceleration/deceleration and constant speed driving, if I0 and I1 are both set to low level, then the driving current of the paper feed motor should be I[sub]TRIPMAX[/sub]=300 mA; while in the holding state, if I0 is set to low level and I1 is set to high level, then the driving current of the paper feed motor should be 1/3, that is: I[sub]TRIPMAX[/sub]=90mA. The figure shows the relevant current waveforms when using this drive circuit. Based on the waveforms, the current during paper feed motor acceleration is 60×5=300 mA (which meets the theoretical value of 300±21 mA); the current during paper feed motor holding state is 17×5=85 mA (which meets the theoretical value of 90±20mA). During the design, the PWM oscillation frequency can be fixed at around 25 kHz. In fact, under the control of the low-voltage control circuit, the chip will stop when the motor power supply and logic power supply are below the operating voltage range to prevent malfunctions and abnormal losses. During this stop state, all output lines are OFF. When the internal PWM is OFF, the load current will recover. During this period, the SPI-7210M can turn on the MOSFET (insulated-gate field-effect transistor, see the internal block diagram in Figure 1) at the appropriate time. The MOSFET does not flow into the drive transistor; instead, current flows into the low-resistance MOSFET itself, thus reducing the drive's own losses and lowering the overall chip temperature rise. Therefore, no additional Schottky diode is needed externally to the SPI-7210M chip. Comparison with UDN2916LB Figure 4 shows a comparison of motor drive circuits based on UDN2916LB and SPI-7210M. Table 3 shows a comparison of several key parameters. The power loss and temperature rise in Table 3 were obtained under 24V/0.4A conditions. In fact, the main differences between UDN2916LB and SPI-7210M are as follows: (1) UDN2916LB is a product of Allegro more than 20 years ago, with relatively backward technology, larger package, and more heat generation; while SPI-7210M is a product of SANKEN in 2005, using the current advanced technology in the industry, with a smaller package and less heat generation. (2) SPI-7210M fixes the PWM oscillation frequency to about 25 kHz, reducing the number of external resistors and capacitors; while the PWM oscillation frequency of UDN2916LB needs to be adjusted by connecting resistors and capacitors outside the chip, which increases the space occupied by the device on the PCB. Since the capacitance value is greatly affected by temperature, and in the design, the resistors and capacitors are generally placed close to the driver chip, the heat generation of the driver chip will directly affect the working temperature of the resistors and capacitors, which will cause the PWM oscillation frequency affected by the resistors and capacitors to shift after the temperature rises, thus causing the deviation of the drive current, and eventually burning out the motor or the driver chip itself (and there are similar hidden dangers when the ambient temperature changes). In the design and production process, I have found that the burnout of the drive chip and motor is often related to the improper selection of external resistors and capacitors. (3) When the load current rises, the MOSFET inside the SPI-7210M will consume most of the current due to its low internal resistance, which can reduce the loss of the drive transistor itself and reduce the temperature rise of the entire chip; while the UDN2916LB requires four Schottky diodes to be connected to the output to disperse some of the heat generated during the current rise and reduce the temperature rise of the drive chip itself. (4) Cost advantage: At present, the market reference price of SPI-7210M is about 1.5 yuan cheaper than UDN2916LB; for the whole control scheme, since the SPI-7210M has four fewer resistors, four fewer capacitors and four fewer Schottky diodes, the overall cost of the scheme can be reduced by 2 to 2.5 yuan; if we add the cost of the reduced PCB area due to the smaller package of SPI-7210M and the reduced PCB area of ​​the external components, its cost advantage and reduction will be more obvious. (5) In terms of software control, the SPI-7210M is completely consistent with the UDN2916LB; that is to say, for older UDN2916LB products, only minor modifications to the relevant hardware parameters and circuits are needed to use the SPI-7210M, without any software changes. Therefore, replacement is relatively convenient. Conclusion Compared with the current mainstream product UDN2916LB, the SPI-7210M has fewer external components, lower losses, lower overall cost, and less PCB space required; at the same time, no software changes are needed during replacement, making it relatively convenient. This chip has been used in large quantities in foreign products and has been reliably verified, but its use in China is still relatively limited. Currently, this chip has been verified by the author in small batches, and overall, its performance is relatively stable, which can effectively improve the reliability of products. References [1] He Limin, Design of Single-Chip Microcomputer Application System [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 1999. [2] Gao Zhongmin, Design of Mechatronics System [M]. Beijing: Machinery Industry Press, 1997. [3] Wang Xiaoming, Single-Chip Microcomputer Control of Electric Motor [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2002.