SLVSCH4 July   2014 DRV8842-EP

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Schematic
  5. 5 Revision History
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Motor Driver Timing Requirements
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 PWM Motor Drivers
      2. 8.3.2 Bridge Control
      3. 8.3.3 Current Regulation
      4. 8.3.4 Blanking Time
      5. 8.3.5 nRESET and nSLEEP Operation
      6. 8.3.6 Protection Circuits
        1. 8.3.6.1 Overcurrent Protection (OCP)
        2. 8.3.6.2 Thermal Shutdown (TSD)
        3. 8.3.6.3 Undervoltage Lockout (UVLO)
      7. 8.3.7 Thermal Protection
      8. 8.3.8 Heatsinking
    4. 8.4 Device Functional Modes
      1. 8.4.1 Decay Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Power Dissipation
        2. 9.2.2.2 Current Regulation Considerations
        3. 9.2.2.3 Slow, Fast, and Mixed Decay Modes
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Bulk Capacitance
    2. 10.2 Power Supply and Logic Sequencing
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Trademarks
    2. 12.2 Electrostatic Discharge Caution
    3. 12.3 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9 Application and Implementation

9.1 Application Information

The DRV8842-EP is used in DC motor control. This integrated driver drives up to a 5-A peak with precise winding current control.  The motor is controlled through a PWM interface and device faults are reported through the nFAULT pin. The following design is a common application of the DRV8842-EP.

9.2 Typical Application

typ_app_SLVSCH4.gif

9.2.1 Design Requirements

Design Parameters Reference Example Value
Supply voltage VM 24 V
Motor winding resistance RL 13.23 Ω
Motor winding inductance IL 4.03 mH
Motor type BDC Brushed DC motor
Sense resistor RSENSE 100 mΩ
Full-scale current IFS 3.5 A

9.2.2 Detailed Design Procedure

9.2.2.1 Power Dissipation

Average power dissipation in the DRV8842-EP when running a DC motor can be roughly estimated by Equation 2.

Equation 2. eq2_lvsab7.gif

where

  • P is the power dissipation of one H-bridge
  • RDS(ON) is the resistance of each FET
  • IOUT is the RMS output current being applied to each winding

IOUT is equal to the average current drawn by the DC motor. Note that at start-up and fault conditions, this current is much higher than normal running current; also consider the peak currents and their duration. The factor of 2 is due to two FETs conducting winding current (one high side and one low side) at any instant.

The maximum amount of power that can be dissipated in the device depends on ambient temperature and heatsinking.

Note that RDS(ON) increases with temperature, so as the device heats, the power dissipation increases. Take this into consideration when sizing the heatsink.

9.2.2.2 Current Regulation Considerations

For the DRV8842-EP, the set full-scale current (IFS) is the maximum current that can be driven. This quantity depends on the VREF analog voltage and the sense resistor value (RSENSE). The gain of DRV8842-EP is set for 5 V/V. This value can be adjusted from 0% to 100% through the use of the relative current bits I[4:0].

Equation 3. eq_I_FS_LVSCH4.gif

To achieve IFS = 3.5 A with RSENSE of 0.1 Ω, V(VREF) should be 1.75 V, and I[4:0] should be 0x1F.

9.2.2.3 Slow, Fast, and Mixed Decay Modes

The DRV8842-EP supports three different decay modes: slow decay, fast decay, and mixed decay. The current through the motor winding is regulated using a fixed-frequency PWM scheme. This means that after any drive phase, when a motor winding current has hit the current chopping threshold (ITRIP), the DRV8842-EP places the winding in one of the three decay modes until the PWM cycle has expired. After, a new drive phase starts.

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.

9.2.3 Application Curves

25_fwd_LVSCH4.gif
Figure 6. 25% Duty Cycle, Forward Direction
25_rev_LVSCH4.gif
Figure 8. 25% Duty Cycle, Reverse Direction
75_fwd_LVSCH4.gif
Figure 7. 75% Duty Cycle, Forward Direction
75_rev_LVSCH4.gif
Figure 9. 75% Duty Cycle, Reverse Direction