SLVSA73F April   2010  – July 2014 DRV8825


  1. Features
  2. Applications
  3. Description
  4. Simplified Schematic
  5. Revision History
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 PWM Motor Drivers
      2. 8.3.2 Current Regulation
      3. 8.3.3 Decay Mode
      4. 8.3.4 Blanking Time
      5. 8.3.5 Microstepping Indexer
      6. 8.3.6 nRESET, nENBL, and nSLEEP Operation
      7. 8.3.7 Protection Circuits
        1. Overcurrent Protection (OCP)
        2. Thermal Shutdown (TSD)
        3. Undervoltage Lockout (UVLO)
    4. 8.4 Device Functional Modes
      1. 8.4.1 STEP/DIR Interface
      2. 8.4.2 Microstepping
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. Stepper Motor Speed
        2. Current Regulation
        3. Decay Modes
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Bulk Capacitance
    2. 10.2 Power Supply and Logic Sequencing
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Protection
      1. 11.3.1 Power Dissipation
      2. 11.3.2 Heatsinking
  12. 12Device and Documentation Support
    1. 12.1 Trademarks
    2. 12.2 Electrostatic Discharge Caution
    3. 12.3 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9 Application and Implementation

9.1 Application Information

The DRV8825 is used in bipolar stepper control. The microstepping motor driver provides additional precision and a smooth rotation from the stepper motor. The following design is a common application of the DRV8825.

9.2 Typical Application


9.2.1 Design Requirements

Design Parameter Reference Example Value
Supply Voltage VM 24 V
Motor Winding Resistance RL 3.9 Ω
Motor Winding Inductance IL 2.9 mH
Motor Full Step Angle θstep 1.8°/step
Target Microstepping Level nm 8 µsteps per step
Target Motor Speed v 120 rpm
Target Full-Scale Current IFS 1.25 A

9.2.2 Detailed Design Procedure Stepper Motor Speed

The first step in configuring the DRV8825 requires the desired motor speed and microstepping level. If the target application requires a constant speed, then a square wave with frequency ƒstep must be applied to the STEP pin.

If the target motor startup speed is too high, the motor will not spin. Make sure that the motor can support the target speed or implement an acceleration profile to bring the motor up to speed.

For a desired motor speed (v), microstepping level (nm), and motor full step angle (θstep),

Equation 2. eq_fstep_1_LVSA06.gif

Equation 3. eq_fstep_2_LVSA06.gif

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

For the DRV8825, the microstepping level is set by the MODE pins and can be any of the settings in Table 1. Higher microstepping will mean a smoother motor motion and less audible noise, but will increase switching losses and require a higher ƒstep to achieve the same motor speed. Current Regulation

In a stepper motor, the set full-scale current (IFS) is the maximum current driven through either winding. This quantity depends on the xVREF analog voltage and the sense resistor value (RSENSE). During stepping, IFS defines the current chopping threshold (ITRIP) for the maximum current step. The gain of DRV8825 is set for 5 V/V.

Equation 4. eq_Ifs_LVSA06.gif

To achieve IFS = 1.25 A with RSENSE of 0.2 Ω, xVREF should be 1.25 V. Decay Modes

The DRV8825 supports three different decay modes: slow decay, fast decay, and mixed decay. The current through the motor windings is regulated using a fixed-frequency PWM scheme. This means that after any drive phase, when a motor winding current has hit the current chopping threshold (ITRIP), the DRV8825 will place the winding in one of the three decay modes until the PWM cycle has expired. Afterward, a new drive phase starts.

The blanking time, tBLANK, defines the minimum drive time for the current chopping. ITRIP is ignored during tBLANK, so the winding current may overshoot the trip level.

9.2.3 Application Curves

Figure 8. Microstepping Current (Phase A) vs STEP Input, Mixed Decay
Figure 10. Microstepping Current (Phase A) vs STEP Input, Mixed Decay on Decreasing Steps
Figure 9. Microstepping Current (Phase A) vs STEP Input, Slow Decay on Increasing Steps