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Accurate and highly efficient stepper motor control

How semiconductor advances can drive improved motor control

Stepper motors are integrated into applications where precise control is a basic operating requirement. From printers and vending machines, to industrial robots, stepper motors are often the only option. To achieve their precision, designers need to ensure that the rotor never loses synchronization as a result of stalling. In order to compensate, a current margin that is sufficient to prevent heavy torque changes, is normally used.

Application of a constant current results in a significant loss in drive efficiency. This extra, unused energy is dissipated in the stepper motor coils as heat, as well as in the electronic drive circuitry. It is possible to adjust the current applied by implementing real-time monitoring, but this requires significant design effort, sensing circuitry, and control algorithm development.

In order to simplify the development of highly-efficient stepper motor drives, Toshiba has developed their Active Gain Control (AGC) stall prevention technology. Through the implementation of a closed-loop control system, the technology compensates for changes in motor torque, applying the correct amount of current as demanded by the application. This still ensures that the motor does not stall while also achieving an optimal power efficiency that cannot be achieved using conventional motor control drivers.

The AGC technology results in power consumption reduction of up to 30 % compared to conventional motor control solutions. Additionally, the silicon control chip operates at a temperature of around 30 °C lower than when AGC is not used. This is all achieved without the need to resort to microcontrollers, ADCs or sensors.

Devices such as the TB67S128FTG offer clock-in controlled bipolar stepper-motor drive with control down to a resolution of 1/128. It also includes an in-built sense resistor, negating the need for a separate sense resistor. Utilizing a BiCD process, the device is rated at 50 V and can handle drive currents of up to 5 A. An integrated 5 V regulator enables the use of a single power supply. In addition, error detection features, such as over current and thermal shutdown, are also implemented.

Toshiba also provide a comprehensive reference design to speed up development with this stepper motor driver. The package includes an application note, bill-of-materials (BOM), schematic, and gerber files. To download your free AGC design package, please click here:

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·Before creating and producing designs and using, customers must also refer to and comply with the latest versions of all relevant TOSHIBA information and the instructions for the application that Product will be used with or for.