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

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9 Power Supply Recommendations

9.1 Bulk Capacitance

Having an appropriate local bulk capacitance is an important factor in motor-drive system design. It is generally beneficial to have more bulk capacitance, while the disadvantages are increased cost and physical size.

The amount of local capacitance needed depends on a variety of factors, including:

  • The highest current required by the motor system
  • The power supply capacitance and ability to source current
  • The amount of parasitic inductance between the power supply and motor system
  • The acceptable voltage ripple
  • The type of motor used (brushed dc, brushless dc, stepper)
  • The motor braking method

The inductance between the power supply and the motor drive system limits the rate current can change from the power supply. If the local bulk capacitance is too small, the system responds to excessive current demands or dumps from the motor with a change in voltage. When adequate bulk capacitance is used, the motor voltage remains stable and high current can be quickly supplied.

The device data sheet generally provides a recommended value, but system-level testing is required to determine the appropriate sized bulk capacitor.

DRV8811 power_supply_rec_SLVS865.gif Figure 13. Example Setup of Motor Drive System With External Power Supply

The voltage rating for bulk capacitors should be higher than the operating voltage, to provide margin for cases when the motor transfers energy to the supply.