SLVSCH0 April   2014 DRV8824-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Schematic
  5. 5 Revision History
  6. 6 Terminal Configuration and Functions
  7. 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. 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 Blanking Time
      4. 8.3.4 Microstepping Indexer
      5. 8.3.5 nRESET, nENBLE and nSLEEP Operation
      6. 8.3.6 Protection Circuits
        1. 8.3.6.1 Overcurrent Protection (OCP)
        2. 8.3.6.2 Thermal Shutdown (TSD)
        3. 8.3.6.3 Undervoltage Lockout (UVLO)
      7. 8.3.7 Thermal Information
        1. 8.3.7.1 Thermal Protection
        2. 8.3.7.2 Power Dissipation
        3. 8.3.7.3 Heatsinking
    4. 8.4 Device Functional Modes
      1. 8.4.1 Decay Mode
  9. 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. 9.2.2.1 Stepper Motor Speed
        2. 9.2.2.2 Current Regulation
        3. 9.2.2.3 Decay Modes
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  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

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メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

9 Application and Implementation

9.1 Application Information

The DRV8824-Q1 is used in bipolar stepper control. The following design procedure can be used to configure the DRV8824-Q1.

9.2 Typical Application

typ_app_schematic_slvsch0.gifFigure 8. Typical Application Schematic

9.2.1 Design Requirements

Table 3 gives design input parameters for system design.

Table 3. Design Parameters

DESIGN PARAMETER REFERENCE EXAMPLE VALUE
Supply voltage VM 24 V
Motor winding resistance RL 1.0 Ω/phase
Motor winding inductance LL 3.5 mH/phase
Motor full step angle θstep 1.8°/step
Target microstepping level nm 8 microsteps per step
Target motor speed v 120 rpm
Target full-scale current IFS 1.25 A

9.2.2 Detailed Design Procedure

9.2.2.1 Stepper Motor Speed

The first step in configuring the DRV8824-Q1 requires the desired motor speed and microstepping level. If the target application requires a constant speed, then a square wave with frequency fstep must be applied to the STEP pin.

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), microstepping level (nm), and motor full step angle (θstep),

Equation 3. eq3_fstep_slvsch0.gif

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

For the DRV8824-Q1, the microstepping level is set by the USM pins and can be any of the settings in . Higher microstepping will mean a smother motor motion and less audible noise, but will increase switching losses and require a higher fstep to achieve the same motor speed.

9.2.2.2 Current Regulation

In a stepper motor, the full-scale current (IFS) is the maximum current driven through either winding. This quantity will depend on the VREF analog voltage and the sense resistor value (RSENSE). During stepping, IFS defines the current chopping threshold (ITRIP) for the maximum current step.

Equation 4. eq4_Ifs_slvsch0.gif

IFS is set by a comparator which compares the voltage across RSENSE to a reference voltage. There is a current sense amplifier built in with programmable gain through ISGAIN. Note that IFS must also follow the equation below in order to avoid saturating the motor. VM is the motor supply voltage and RL is the motor winding resistance.

Equation 5. eq5_Ifs_slvsch0.gif

9.2.2.3 Decay Modes

The DRV8824-Q1 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 DRV8824-Q1 will place the winding in one of the three decay modes until the PWM cycle has expired. Afterwards, 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

typ_app1_slvsch0.gifFigure 9. Microstepping Waveform, Phase A, Mixed Decay
typ_app3_slvsch0.gifFigure 11. Microstepping Waveform, Mixed Decay on Decreasing Steps
typ_app2_slvsch0.gifFigure 10. Microstepping Waveform, Slow Decay on Increasing Steps