SLVAFF1 January   2023 DRV8452 , DRV8462

PRODUCTION DATA  

  1.   Abstract
  2.   Trademarks
  3. 1Power Efficiency of Stepper Motor Drivers
  4. 2Auto-Torque
    1. 2.1 Auto-Torque: Learning Principle
      1. 2.1.1 Configuring Auto-Torque Learning Routine
    2. 2.2 Current Control
      1. 2.2.1 Setting Current Control Parameters
    3. 2.3 PD Control Loop
    4. 2.4 Impact of Auto-Torque Tuning Parameters
      1. 2.4.1 Impact of Learning Parameters on Load Transient Response
      2. 2.4.2 Impact of ATQ_UL, ATQ_LL Hysteresis
      3. 2.4.3 Impact of Load Profile on Power Saving
      4. 2.4.4 Adaptive ATQ_UL, ATQ_LL
      5. 2.4.5 PD Parameter Dependency Curves
        1. 2.4.5.1 Dependency on KP
        2. 2.4.5.2 Dependency on KD and ATQ_D_THR
        3. 2.4.5.3 Dependency on ATQ_FRZ and ATQ_AVG
        4. 2.4.5.4 Dependency on ATQ_ERROR_TRUNCATE
      6. 2.4.6 ATQ_CNT at Different Motor Speeds
      7. 2.4.7 ATQ_CNT at Different Supply Voltages
      8. 2.4.8 Motor Temperature Estimation
    5. 2.5 Efficiency Improvement With Auto-Torque
  5. 3Case Studies
    1. 3.1 Application 1: ATM Machines
      1. 3.1.1 ATM Motor Operating Conditions
      2. 3.1.2 ATM Motor With Auto-Torque
    2. 3.2 Application 2: Textile Machines
      1. 3.2.1 Textile Motor Operating Conditions
      2. 3.2.2 Textile Motor With Auto-Torque
    3. 3.3 Application 3: Printer
      1. 3.3.1 Printer Motor With Auto-Torque
  6. 4Summary
  7. 5References

1 Power Efficiency of Stepper Motor Drivers

Stepper motors are popular due to their simplicity of translating excitation changes on the input to precise positional changes on the output without using any external sensor to monitor position. The currents in stepper coils are regulated to achieve precise position and velocity control.

Torque equation for a motor is given by Equation 1. It depends on coil current and motor construction:

Equation 1. τ m a x   =   K T   × I

where τmax is the maximum supported torque, KT is motor’s torque constant and I is the coil current.

Equation 1 can be interpreted as torque capability offered by coil current I. To sustain a given load torque, the motor driver must always operate at a coil current which can offer more torque than demanded.

Conventional motor drivers configure operating full-scale current based on the peak load torque demand. This ensures that the motor does not lose steps any time peak load is demanded. The current therefore is constant irrespective of the load torque. As a result, when load torque is lower than the peak load, the driver and the motor dissipate some of the input power as resistive power loss as represented in Figure 1-1.

Figure 1-1 Power Loss With Conventional Stepper Driver

In most systems, the demand for peak load torque occurs only rarely. For example, in an ATM machine, the stepper motors might be needed to deliver peak load for less than 15% of their overall run time. A typical stepper driver though ends up delivering full-scale current to the motors all the time - leading to lower system efficiency due to the unwanted power loss, larger system size and shorter lifetime of components.