More and more cars are equipped with power windows, and the control circuit of the stepper motor is particularly critical to the overall quality of the power windows. Below is a practical drive circuit for a stepper motor in automotive power windows. This circuit uses the MTD2005F, a two-phase bipolar stepper motor driver integrated circuit from SHINDENGEN, which is particularly suitable for controlling high-power automotive power window stepper motors. The MTD2005F is a two-phase motor constant current drive chip that integrates power devices and control logic. It requires some simple external connections to achieve constant current chopper control of the motor. The constant current drive circuit of the MTD2005F is shown in Figure 1, and the motor coil circuit is shown in Figure 2. The circuit operation is as follows. Figure 1 Schematic diagram of constant current drive of MTD2005F Figure 2 Schematic diagram of motor coil circuit (1) External signal controls Q1 and Q2 to turn on, generating current A (power supply → Q1 → motor coil → Q2 → Rs → ground). Current A is converted into voltage Vs through sampling resistor Rs. When Vs rises to the reference voltage Vref, the current comparator outputs a control signal to turn off Q1. (2) When constant current control is activated, Q1 is turned off, and the inductance of the coil generates current B (ground → Dfw → motor coil → Q2 → Rs → ground). (3) After the chopping cycle T, Q1 is turned on again, generating current A again. The current rises again, and when Vs rises to the reference voltage Vref, Q1 is turned off again. After this, the second and third steps are continuously cycled. (4) External signal turns off Q1 and Q2, generating current C (ground → Dfw → motor coil → Dfb → power supply), and the current drops rapidly. Design of driving current The design of driving current Ip is shown in the following formula. Ip = (5·R3)/(R2+R3)·N·(1/RS) Where R2 and R3 are as shown in the example; Rs is the current sampling resistor, such as R6 and R7 in the example; N is the percentage of PWM. During motor operation, if the control system modifies the PWM value, the motor's drive current Ip will change. This is important in practical applications. For example, if the motor needs to accelerate and decelerate, the motor drive current should ideally be changed. Chopper Frequency Design Chopper period T = 0.72Ct·Rt Chopper frequency f = 1/T To avoid noise in the audio range, the chopper frequency f is usually set to at least 20kHz. However, if the frequency is too high, it will increase the power consumption of the integrated chip and increase heat generation. It is recommended that Ct = 4700pF (2200～4700pF), Rt = 13kΩ (10～40kΩ), and the maximum chopper frequency f be 30kHz. Power Reduction Design Inserting a Schottky diode between the output terminal and power ground can reduce the power consumption of the IC driver chip, as shown in Figure 3. Figure 3: Power Reduction Circuit Diagram; Figure 4: Acceleration/Deceleration Curve Example. These external Schottky diodes can shunt most of the freewheeling current, thereby reducing the internal power consumption of the chip. The effectiveness of power reduction also depends on the inserted Schottky diode; it is recommended to use the D1FS4 Schottky diode from SHINDENGEN. Output Current Logic Control Phase A and B control the direction of the current. In the case of 1-2 excitation, ENA A and B are used in combination. The truth table and control sequence are shown below. Stepper Motor Acceleration/Deceleration Design Through the logic control of the output current, the stepper motor can be made to rotate forward or backward. To reduce noise and shaking during the operation of the electric window, the stepper motor needs to be able to smoothly accelerate to a certain speed or decelerate to a stop. There are generally two types of acceleration/deceleration curves: progressive and stepped. In automotive electric window applications, the stepped curve is more effective in practical use. The stepped acceleration/deceleration curve is shown in Figure 5. Figure 5: Practical Example Schematic Diagram and Application Example The circuit principle of the application example is shown in Figure 5. The PWM design value is 50%, and the parameters of the components used are as follows. U1: MTD2005F U2: 74HCT07 R1: 13K, 1% R2: 10K, 1% R3: 1K, 1% R4, R5: 10K R6, R7: 0.33Ω, 1W, 1% C1: 4700pF, 5% C2, C3: 1000pF C4: 47μF, 50V C5: 0.1μF D1, D2, D3, D4: D1FS4 Theoretical chopping frequency: f＝1/0.72·4700·10-12·13·103=22.7kHz; Theoretical driving current: Ip=（5×1）/（10+1）×50% ×（1/0.33）=0.68A; The actual measurement results are shown in Figure 6. The chopping frequency is 23kHz and the driving current is 700mA, which meets the design requirements. Figure 6. Actual test current waveform