ZHCSDY9A June   2015  – July 2015 DRV8881

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 修订历史记录
  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 Diagrams
    3. 7.3 Feature Description
      1. 7.3.1  Motor Driver Current Ratings
        1. 7.3.1.1 Peak Current Rating
        2. 7.3.1.2 RMS Current Rating
        3. 7.3.1.3 Full-Scale Current Rating
      2. 7.3.2  PWM Motor Drivers
      3. 7.3.3  Bridge Control
      4. 7.3.4  Current Regulation
      5. 7.3.5  Decay Modes
        1. 7.3.5.1 Mode 1: Slow Decay
        2. 7.3.5.2 Mode 2: Fast Decay
        3. 7.3.5.3 Mode 3: 30%/70% Mixed Decay
      6. 7.3.6  AutoTune
      7. 7.3.7  Adaptive Blanking Time
      8. 7.3.8  Parallel Mode
      9. 7.3.9  Charge Pump
      10. 7.3.10 LDO Voltage Regulator
      11. 7.3.11 Logic and Tri-Level Pin Diagrams
      12. 7.3.12 Protection Circuits
        1. 7.3.12.1 VM Undervoltage Lockout (UVLO)
        2. 7.3.12.2 VCP UVLO (CPUV)
        3. 7.3.12.3 Overcurrent Protection (OCP)
        4. 7.3.12.4 Thermal Shutdown (TSD)
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 DRV8881P Typical Application
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Current Regulation
          2. 8.2.1.2.2 Stepper Motor Speed
          3. 8.2.1.2.3 Decay Modes
          4. 8.2.1.2.4 Sense Resistor
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Alternate Application
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Current Regulation
        3. 8.2.2.3 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
  11. 11器件和文档支持
    1. 11.1 文档支持
      1. 11.1.1 相关文档
    2. 11.2 社区资源
    3. 11.3 商标
    4. 11.4 静电放电警告
    5. 11.5 Glossary
  12. 12机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

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 DRV8881 is used in stepper or brushed motor control.

8.2 Typical Applications

8.2.1 DRV8881P Typical Application

The following design procedure can be used to configure the DRV8881. In this application, the DRV8881P will be used to drive a stepper motor.

DRV8881 typ_app_lvsd19.gifFigure 24. Typical Application Schematic

8.2.1.1 Design Requirements

Table 9 gives design input parameters for system design.

Table 9. Design Parameters

DESIGN PARAMETER REFERENCE EXAMPLE VALUE
Supply voltage VM 24 V
Motor winding resistance RL 4.5 Ω/phase
Motor winding inductance LL 10.5 mH/phase
Motor full step angle θstep 1.8°/step
Target microstepping level nm Non-circular 1/2 step
Target motor speed v 120 rpm
Target full-scale current IFS 800 mA

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Current Regulation

In a stepper motor, the full-scale current (IFS) is the maximum current driven through either winding. This quantity will depend on the TRQ pins, the xVREF analog voltage, and the sense resistor value (RSENSE). AVREF and BVREF can be configured to drive different currents, but in this example the same full-scale current is used in both coils.

Equation 2. DRV8881 eq_I_FS_1_lvsd19.gif

TRQ is a DAC used to scale the output current. The current scalar value for different inputs is shown in Table 10.

Table 10. Torque DAC Settings

TRQ1 TRQ0 CURRENT SCALAR (TRQ)
1 1 25%
1 0 50%
0 1 75%
0 0 100%
Example: If the desired full-scale current is 800 mA
Set RSENSE = 250 mΩ, assume TRQ = 100%.
xVREF would have to be 1.32 V.
Create a resistor divider from V3P3 (3.3 V) to set AVREF and BVREF ≈ 1.32 V.
Set R2 = 10 kΩ, set R1 = 15 kΩ

Note that IFS must also follow Equation 3 in order to avoid saturating the motor. VM is the motor supply voltage, and RL is the motor winding resistance.

Equation 3. DRV8881 eq_I_FS_2_lvsd18.gif

8.2.1.2.2 Stepper Motor Speed

Next, the driving waveform needs to be planned. In order to command the correct speed, determine the frequency of the input waveform.

If the target motor speed is too high, the motor will not spin. Make sure that the motor can support the target speed.

For a desired motor speed (v), microstepping level (nm), and motor full step angle (θstep),

Equation 4. DRV8881 eq_fstep_1_lvsd18.gif

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

The frequency ƒstep gives the frequency of input change on the DRV8881P. 1/ ƒstep = tSTEP on the diagram below.

Equation 5. DRV8881 eq_fstep_2_lvsd19.gif
DRV8881 tim_step_motor_lvsd19.gifFigure 25. Example 1/2 Stepping Operation

8.2.1.2.3 Decay Modes

The DRV8881 supports several different decay modes: slow decay, fast decay, mixed decay, and AutoTune (DRV8881E only). The current through the motor windings is regulated using an adjustable fixed-time-off scheme. This means that after any drive phase, when a motor winding current has hit the current chopping threshold (ITRIP), the DRV8881 will place the winding in one of the decay modes for TOFF. After TOFF, a new drive phase starts.

8.2.1.2.4 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 × R. For example, if the rms motor current is 1.4 A and a 250 mΩ sense resistor is used, the resistor will dissipate 1.4 A2 × 0.25 Ω = 0.49 W. The power quickly increases with higher current levels.

Resistors typically have a rated power within some ambient temperature range, along with a derated 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.

8.2.1.3 Application Curve

DRV8881 app_01_lvsd18.gif
Figure 26. DRV8881P Inputs and Output Current Waveform

8.2.2 Alternate Application

In this application, the DRV8881P will be operated in parallel mode in order to drive a single brushed-DC motor.

DRV8881 alt_app_lvsd19.gifFigure 27. Typical Application Schematic

8.2.2.1 Design Requirements

Table 11 gives design input parameters for system design.

Table 11. Design Parameters

DESIGN PARAMETER REFERENCE EXAMPLE VALUE
Supply voltage VM 24 V
Motor winding resistance RL 6 Ω
Motor winding inductance LL 4.1 mH
Target maximum motor current ITRIP 2 A

8.2.2.2 Detailed Design Procedure

8.2.2.2.1 Current Regulation

The maximum current (ITRIP) is set by the TRQ pins, the xVREF analog voltage, and the sense resistor value (RSENSE). In parallel mode the winding current is set by AVREF only and BVREF is ignored. 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 startup.

Example: If the desired regulation current is 2 A
Set RSENSE = 100 mΩ, assume TRQ = 100%.
AVREF would have to be 1.32 V.
Create a resistor divider from V3P3 (3.3 V) to set AVREF ≈ 1.32 V: Set R2 = 10 kΩ, set R1 = 15 kΩ

8.2.2.3 Application Curves

DRV8881 app_02_lvsd19.gif
Figure 28. DRV8881P Startup Current Waveform Without Current Regulation
DRV8881 app_04_lvsd19.gif
Figure 30. DRV8881P Startup Current Waveform With 2-A Current Regulation
DRV8881 app_03_lvsd19.gif
Figure 29. DRV8881P Startup Current Waveform Without Current Regulation (Zoomed In)
DRV8881 app_05_lvsd19.gif
Figure 31. DRV8881P Startup Current Waveform With 2-A Current Regulation (Zoomed In)
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