SLVSAX9G September   2011  – November 2025 DRV8818

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements
    7. 5.7 Motor Driver Timing Switching Characteristics
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 PWM H-Bridge Drivers
      2. 6.3.2 Current Regulation
      3. 6.3.3 Decay Mode
      4. 6.3.4 Microstepping Indexer
      5. 6.3.5 Protection Circuits
        1. 6.3.5.1 Overcurrent Protection (OCP)
        2. 6.3.5.2 Thermal Shutdown (TSD)
        3. 6.3.5.3 Undervoltage Lockout (UVLO)
    4. 6.4 Device Functional Modes
      1. 6.4.1 Sleep Mode
      2. 6.4.2 Disable Mode
      3. 6.4.3 Active Mode
      4. 6.4.4 Decay Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Stepper Motor Speed
        2. 7.2.2.2 Current Regulation
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Bulk Capacitance
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 Heatsinking
      2. 7.4.2 Layout Example
      3. 7.4.3 Thermal Considerations
        1. 7.4.3.1 Power Dissipation
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

6.3.2 Current Regulation

The PWM chopping current is set by a comparator, which compares the voltage across a current sense resistor, multiplied by a factor of 8, with a reference voltage. The reference voltage is input from the VREF pin. The full-scale (100%) chopping current is calculated as follows:

Equation 1. ICHOPA=VVREF(V)8×RSENSE(Ω)

Example:

If a 0.22Ω sense resistor is used and the VREFx pin is 3.3V, the full-scale (100%) chopping current is
3.3V / (8 × 0.22Ω) = 1.875A.

The reference voltage is also scaled by an internal DAC that allows torque control for fractional stepping of a bipolar stepper motor, as described in the Section 6.3.4 section.

When a winding is activated, the current through the winding rises until the chopping current threshold described above is reached, then the current is switched off for a fixed off time. The off time is determined by the values of a resistor and capacitor connected to the RCA (for bridge A) and RCB (for bridge B) pins. The off time is approximated by:

Equation 2. tOFFμs=RkΩ×CnF

To avoid falsely tripping on transient currents when the winding is first activated, a blanking period is used immediately after turning on the FETs, during which the state of the current sense comparator is ignored. The blanking time is determined by the value of the capacitor connected to the RCx pin and is approximated by:

Equation 3. tBLANKns=1400Ω×CnF