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  • Microstepping circuit for stepper motors

  • Created: May 17, 2016

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Summary

The stepper motor is a DC motor that spins one step at a time, compared to other motors, which spin continuously. The rotation of the stepper motor is incremental; because of these no feedback information is needed about its position. A stepper motor with microstepping can improve the performance of the motor especially at very low rpm. This reference design is a microstepping circuit for stepper motor that features the TC4469 logic input CMOS Quad drivers/MOSFET drivers. This MOSFET driver unlike other MOSFET drivers has two inputs for each output (AND/INV).


The circuit’s controller is built around the microcontroller. The speed setting for the circuit is controlled by the potentiometer (R2) connected to the pin RA0, which is one of the ADC channels of the microcontroller. The EN1 and EN2 connection between the microcontroller and the IC bridge driver enables the two sets of bridges in the driver IC. Four PWMs are used in the microcontroller (RC1, RC2, RB2, and RB3). The connections CNT1 and CNT2 (pin RB2 and RB3) switches the connection CCP1 and CCP2 (RC1 and RC2) to appropriate PWM inputs of Driver IC (U2 and U5). The two PWM (RC1 and RC2) modules of PIC18F4520-E/P-ND are used to control current through two windings of the stator, and can be used for both full and half step. The resistors R9 and R10, connected to pin 1 and 15 of U2 are used to convert voltages from current feedbacks of the motor windings. In the I/O pins of the microcontroller, the pin RD5 is connected with a SPST switch for drive enable. The pin RD6 is connected to a push-button switch for motor direction selection (FWD/REV). Each press of the switch will toggle the direction. The pin RD7 is connected to a push-button switch for “inch” movement of the motor. Each press of this switch will move the motor by a step, controlled by software. The DIP (1-3) switches connected to RD0, RD1, and RD2 select the number of steps. A 20MHz crystal is used as the main oscillator. The TC4469 has a high peak output current of 1.2A with an operating voltage supply of 4.5V to 18V. The four PWM are also connected to the MOSFET driver.


The TC4469 is a robust and highly latch-up resistant. They can tolerate up to 5V of noise spiking on the ground line and can handle up to 0.5 of reverse current on the driver outputs. It is ideal for direct driving low current motors or MOSFETs in a H-bridge configuration for high current motor drive. The stepper motor has advantage over other DC motors in terms of positioning, control, incremental, and low speed torque. The incremental and it's repeatable steps make it ideal for application that requires precise positioning and control like automation, robotics, open loop control, and plotters. The stepper motor also is very good at low speed rotation since it has maximum torque at low speeds compared to other dc motors. A stepper motor with a microstepping offers a smooth movement at low speeds, increased step positioning resolution, and maximum torque at both low and high step-rates.

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