SLVSAX9E September   2011  – January 2016 DRV8818

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 Motor Driver Timing Switching Characteristics
    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 H-Bridge Drivers
      2. 7.3.2 Current Regulation
      3. 7.3.3 Decay Mode
      4. 7.3.4 Microstepping Indexer
      5. 7.3.5 Protection Circuits
        1. 7.3.5.1 Overcurrent Protection (OCP)
        2. 7.3.5.2 Thermal Shutdown (TSD)
        3. 7.3.5.3 Undervoltage Lockout (UVLO)
    4. 7.4 Device Functional Modes
      1. 7.4.1 RESETn, ENABLEn, and SLEEPn Operation
      2. 7.4.2 Decay Modes
  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
      1. 10.1.1 Heatsinking
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
      1. 10.3.1 Power Dissipation
  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 DRV8818 is used for bipolar stepper motor control. The microstepping motor driver provides precise regulation of the coil current and ensures a smooth rotation from the stepper motor.

8.2 Typical Application

Figure 9 shows a common system application of the DRV8818.

DRV8818 typ_app_slvsax9.gif Figure 9. Typical Application Schematic

8.2.1 Design Requirements

See Table 3 for the design parameters.

Table 3. Design Parameters

DESIGN PARAMETER REFERENCE EXAMPLE VALUE
Supply Voltage VM 24 V
Motor Winding Resistance RL 4.0 Ω
Motor Winding Inductance IL 3.7 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

8.2.2 Detailed Design Procedure

8.2.2.1 Stepper Motor Speed

The first step in configuring the DRV8818 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 5. DRV8818 equation_6_slvsax9.gif
Equation 6. DRV8818 equation_7_slvsax9.gif

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

For the DRV8818, the microstepping level is set by the USMx pins. 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.

8.2.2.2 Current Regulation

In a stepper motor, the set 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. The gain of DRV8818 is set for 8 V/V.

Equation 7. DRV8818 equation_8_slvsax9.gif

To achieve IFS = 1.25 A with RSENSE of 0.1 Ω, VREF should be 1.56 V.

8.2.3 Application Curves

DRV8818 wvfrm_01_mixed_decay_slvsax9.png Figure 10. Mixed Decay
DRV8818 wvfrm_03_mixed_decay_slvsax9.png Figure 12. Mixed Decay on Decreasing Steps
DRV8818 wvfrm_02_slow_decay_slvsax9.png Figure 11. Slow Decay on Increasing Steps