SLVS912J January   2009  – January 2016 DRV8821

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Dissipation Ratings
    8. 6.8 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 PWM Motor Drivers
      2. 7.3.2 Current Regulation
      3. 7.3.3 Blanking Time
      4. 7.3.4 Microstepping Indexer
      5. 7.3.5 xRESETn and xENBLn Operation
      6. 7.3.6 Protection Circuits
        1. 7.3.6.1 Overcurrent Protection (OCP)
        2. 7.3.6.2 Thermal Shutdown (TSD)
        3. 7.3.6.3 Undervoltage Lockout (UVLO)
        4. 7.3.6.4 Shoot-Through Current Prevention
    4. 7.4 Device Functional Modes
      1. 7.4.1 Decay Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Stepper Motor Speed
        2. 8.2.2.2 Current Regulation
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Bulk Capacitance
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
      1. 10.3.1 Power Dissipation
      2. 10.3.2 Heatsinking
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The DRV8821 can be used to drive two bipolar stepper motors.

8.2 Typical Application

DRV8821 DRV8821_Typical_Application.png Figure 12. Typical Application Schematic

8.2.1 Design Requirements

Table 3 shows the design parameters.

Table 3. Design Parameters

DESIGN PARAMETER REFERENCE EXAMPLE VALUE
Supply voltage VM 24 V
Motor winding resistance RL 7.4 Ω/phase
Motor step full angle θstep 1.8°/step
Target microstepping angle nm 1/8 step
Target motor speed V 120 rpm
Target full-scale current IFS 1 A

8.2.2 Detailed Design Procedure

8.2.2.1 Stepper Motor Speed

The first step in configuring the DRV8821 requires the desired motor speed and stepping level. The DRV8821 can support from full step to 1/8 step mode. If the target motor speed is too high, the motor will not spin. Make sure that the motor can support the target speed. For a desired motor speed (v), a microstepping level (nm), and motor full step angle (θstep).

Equation 2. DRV8821 equation_912.gif

θstep can be found in the stepper motor data sheet or often written on the motor itself.

For DRV8821, the microstepping levels are set by the xUSM0/xUSM1 pins and can be any of the settings in Table 1. Higher microstepping means a smoother motor motion and less audible noise, but increases the switching losses and requires a higher ƒstep to achieve the same motor speed.

8.2.2.2 Current Regulation

The chopping current (ICHOP) is the maximum current driven through either winding. This quality will depend on the sense resistor value (RXISEN).

Equation 3. DRV8821 eq_02_slvs912.gif

ICHOP is set by a comparator which compares the voltage across RXISEN to a reference voltage. Note that ICHOP must follow Equation 4 to avoid saturating the motor.

Equation 4. DRV8821 eq_01_slvs912.gif

where

  • VM is the motor supply voltage.
  • RL is the motor winding resistance.

8.2.3 Application Curves

DRV8821 SLOWDECAY_HALFSTEP.png Figure 13. ½ Step Microstepping with Slow Decay
DRV8821 MIXEDDECAY_HALFSTEP.png Figure 15. 1/2 Step Microstepping with Mixed Decay
DRV8821 SLOWDECAY_EIGHTH_STEP.png Figure 14. 1/8 Step Microstepping with Slow Decay
DRV8821 MIXEDDECAY_EIGHTHSTEP.png Figure 16. 1/8 Step Microstepping with Mixed Decay