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  • 24V Stepper Motor Design with AutoTune

  • Created: Sep 04, 2016

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Summary

This design is an application of Texas Instruments’ DRV8880 stepper motor driver, an integrated motor driver solution for bipolar stepper motors. The device integrates two N-channel power MOSFET H-bridges, current regulation circuitry, and a microstepping indexer. The circuit design showcases how quickly Auto-Tune can adapt to changes in system inputs or motor characteristics without the need to apply any type of parameter tuning.


For stepper motors, a common design problem is tuning, which involves selecting the best decay mode to operate the stepper motor efficiently. A well-behaved current waveform makes a well-behaved stepper that will run smoothly (less vibration), quietly (less noise) and efficiently (less power dissipation). Unfortunately, there are a lot of factors that can affect the waveform, such as supply voltage, motor parameters, motor speed and load. Finding a fixed decay mode to match these settings can sometimes be difficult, especially if these parameters will shift during operation. Auto-Tune greatly simplifies the decay mode selection by automatically configuring the decay mode between slow, mixed, and fast decay. In mixed decay, Auto-Tune dynamically adjusts the fast decay percentage of the total mixed decay time. This feature eliminates motor tuning by automatically determining the best decay setting that results in the lowest ripple for the motor.


To enable the Auto-Tune mode, pull the ATE pin logic high. Ensure the DECAYx pins are logic low. The Auto-Tune mode is registered internally when exiting from sleep mode or the power-up sequence. The ATE pin can be shorted to V3P3 to pull it logic high for this purpose. The decay mode setting is optimized iteratively each PWM cycle. If the motor current overshoots the target trip level, then the decay mode becomes more aggressive (add fast decay percentage) on the next cycle in order to prevent regulation loss. If there is a long drive time to reach the target trip level, the decay mode becomes less aggressive (remove fast decay percentage) on the next cycle in order to operate with fewer ripples and more efficiently. On falling steps, Auto-Tune will automatically switch to fast decay in order to reach the next step quickly.


The DRV8880 stepper motor driver can be used on many applications like automatic teller and money handling machines, video security cameras, multi-function printers and document, scanners, 3D printers, office automation machines, factory automation and robotics.

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