SLVSA74E May   2010  – September 2015 DRV8829

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 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 Motor Drivers
      2. 7.3.2 Blanking Time
      3. 7.3.3 nRESET and nSLEEP Operation
      4. 7.3.4 Protection Circuits
        1. 7.3.4.1 Overcurrent Protection (OCP)
        2. 7.3.4.2 Thermal Shutdown (TSD)
        3. 7.3.4.3 Undervoltage Lockout (UVLO)
      5. 7.3.5 Current Regulation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Bridge Control
      2. 7.4.2 Decay Mode
  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 Sense Resistor
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Bulk Capacitance Sizing
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
    4. 10.4 Power Dissipation
      1. 10.4.1 Heatsinking
  11. 11Device and Documentation Support
    1. 11.1 Community Resources
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 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 DRV8829 is used in brushed motor or stepper control.

8.2 Typical Application

In this application, the DRV8829 will be used to drive a brushed-DC motor. The following design procedure can be used to configure the DRV8829.

DRV8829 typ_app_lvsa74.gifFigure 5. Typical Application Schematic

8.2.1 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 0.83 Ω
Motor winding inductance LL 232.5 µH
Target chopping current ITRIP 3.5 A

8.2.2 Detailed Design Procedure

The maximum current (ITRIP) is set by the Ix pins, the VREF analog voltage, and the sense resistor value (RSENSE). When starting a brushed-DC motor, a large inrush current may occur because there is no back-EMF. Current regulation will act to limit this inrush current and prevent high current on start-up.

Equation 2. DRV8829 eq1_lvs997.gif
Example: If the desired chopping current is 3.5 A
Set RSENSE = 100 mΩ
VREF would have to be 1.75 V.
Create a resistor divider from V3P3OUT (3.3 V) to set VREF ≈ 1.75 V.
Set R2 = 18 kΩ, set R1 = 16 kΩ

8.2.2.1 Sense Resistor

For optimal performance, it is important for the sense resistor to be:

  • Surface-mount
  • Low inductance
  • Rated for high enough power
  • Placed closely to the motor driver

The power dissipated by the sense resistor equals Irms² x R.  For example, if the rms motor current is 2-A and a 100-mΩ sense resistor is used, the resistor will dissipate 2 A² × 0.1 Ω = 0.4 W.  The power quickly increases with greater current levels.

Resistors typically have a rated power within some ambient temperature range, along with a de-rated power curve for high ambient temperatures.  When a PCB is shared with other components generating heat, margin should be added.  It is always best to measure the actual sense resistor temperature in a final system, along with the power MOSFETs, as those are often the hottest components.

Because power resistors are larger and more expensive than standard resistors, it is common practice to use multiple standard resistors in parallel, between the sense node and ground.  This distributes the current and heat dissipation.

8.2.3 Application Curves

DRV8829 app_01_lvsa74.gifFigure 6. Motor Start-up without Current Regulation, Overcurrent Trips
DRV8829 app_03_lvsa74.gifFigure 8. Motor Start-up With Current Regulation, Motor Reaches Steady State
DRV8829 app_02_lvsa74.gifFigure 7. Motor Start-up With Current Regulation