SLVS865J September   2008  – April 2017 DRV8811

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 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
  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. 8.2.2.3 Decay Modes
      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 Information
      1. 10.3.1 Heatsinking
    4. 10.4 Power Dissipation
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 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 application section 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 DRV8811 device 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 DRV8811 device.

DRV8811 typ_app_slvs865.gif Figure 9. Typical Application Schematic

8.2.1 Design Requirements

Table 3. Design Parameters

DESIGN PARAMETER REFERENCE EXAMPLE VALUE
Supply voltage VM 24 V
Motor winding resistance RL 4 Ω
Motor winding inductance IL 3.7 mH
Motor full-step angle θstep 1.8°
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 DRV8811 device 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 start-up speed is too high, the motor does 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. DRV8811 equation_6_slvs865.gif
Equation 6. DRV8811 equation_7_slvs865.gif

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

For the DRV8811 device, the microstepping level is set by the USMx pins. Higher microstepping means a smother motor motion and less audible noise, but increases 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 depends on the VVREF 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 DRV8811 device is set for 8 V/V.

Equation 7. DRV8811 equation_8_slvs865.gif

To achieve IFS = 1.25 A with RSENSE of 0.1 Ω, VVREF should be 1 V.

8.2.2.3 Decay Modes

The DRV8811 device supports three different decay modes: slow decay, fast decay, and mixed decay. The current through the motor windings is regulated using a fixed off-time scheme.

This means that the current increases until it reaches the current chopping threshold (ITRIP), after which it enters the configured decay mode for a fixed period of time. The cycle then repeats after the decay period expires.

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.

8.2.3 Application Curves

DRV8811 wvfrm_01_mixed_decay_slvs865.png
Figure 10. Mixed Decay
DRV8811 wvfrm_03_mixed_decay_slvs865.png
Figure 12. Mixed Decay on Decreasing Steps
DRV8811 wvfrm_02_slow_decay_slvs865.png
Figure 11. Slow Decay on Increasing Steps