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

2.2 Current Control

This section explains how the auto-torque algorithm modifies the motor coil current according to the applied load torque to minimize the resistive losses in the system.

Table 2-2 lists the registers associated with current control.

Table 2-2 Registers for Current Control
Parameter Description
ATQ_UL[7:0]
ATQ_LL[7:0]		 Upper and lower boundaries of the hysteretic band within which ATQ_CNT is controlled by modifying the motor current.
ATQ_TRQ_MIN[7:0]
ATQ_TRQ_MAX[7:0]		 Programmable minimum and maximum current limit when auto-torque is enabled.
ATQ_TRQ_DAC[7:0] Outputs the value of motor current when auto-torque is enabled. ATQ_TRQ_DAC can vary between ATQ_TRQ_MIN and ATQ_TRQ_MAX.
CNT_OFLW The CNT_OFLW flag becomes 1b if ATQ_CNT is more than ATQ_UL.
CNT_UFLW the CNT_UFLW flag becomes 1b if ATQ_CNT is less than ATQ_LL.

As shown in Equation 4, the ATQ_CNT parameter is proportional to the load torque and inversely proportional to the current setting of the stepper driver.

An idealized representation of this relation is shown in Figure 2-5.

Figure 2-5 ATQ_CNT as a Function of Load Torque

The auto-torque algorithm confines the ATQ_CNT within the hysteretic band defined by the user programmable ATQ_UL and ATQ_LL parameters, by modulating the motor current, as shown in Figure 2-5.

  • Maximum amount of load torque that the motor can support without step loss or stall is proportional to the motor current.
  • If load torque demand increases (T1 to T2), the ATQ_CNT goes above the ATQ_UL threshold, and in response, the algorithm brings the ATQ_CNT within the band by increasing the current (I3 to I4).
  • When load torque demand drops (T2 to T1) and ATQ_CNT goes below ATQ_LL, the algorithm reduces the current to bring the ATQ_CNT within the hysteretic band (I5 to I4).