JAJSCX0C October   2015  – November 2018 DRV8885

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      概略回路図
      2.      マイクロステッピング電流の波形
  4. 4 改訂履歴
  5. 5 概要（続き）
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Indexer 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  Stepper Motor Driver Current Ratings
        1. 8.3.1.1 Peak Current Rating
        2. 8.3.1.2 RMS Current Rating
        3. 8.3.1.3 Full-Scale Current Rating
      2. 8.3.2  PWM Motor Drivers
      3. 8.3.3  Microstepping Indexer
      4. 8.3.4  Current Regulation
      5. 8.3.5  Controlling RREF With an MCU
      6. 8.3.6  Decay Modes
        1. 8.3.6.1 Mode 1: Slow Decay for Increasing and Decreasing Current
        2. 8.3.6.2 Mode 2: Slow Decay for Increasing Current, Mixed Decay for Decreasing Current
        3. 8.3.6.3 Mode 3: Mixed Decay for Increasing and Decreasing Current
      7. 8.3.7  Blanking Time
      8. 8.3.8  Charge Pump
      9. 8.3.9  LDO Voltage Regulator
      10. 8.3.10 Logic and Multi-Level Pin Diagrams
      11. 8.3.11 Protection Circuits
        1. 8.3.11.1 VM Undervoltage Lockout (UVLO)
        2. 8.3.11.2 VCP Undervoltage Lockout (CPUV)
        3. 8.3.11.3 Overcurrent Protection (OCP)
        4. 8.3.11.4 Thermal Shutdown (TSD)
    4. 8.4 Device Functional Modes
  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 Stepper Motor Speed
        2. 9.2.2.2 Current Regulation
        3. 9.2.2.3 Decay Modes
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Bulk Capacitance
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12デバイスおよびドキュメントのサポート
    1. 12.1 ドキュメントのサポート
      1. 12.1.1 関連資料
    2. 12.2 ドキュメントの更新通知を受け取る方法
    3. 12.3 コミュニティ・リソース
    4. 12.4 商標
    5. 12.5 静電気放電に関する注意事項
    6. 12.6 Glossary
  13. 13メカニカル、パッケージ、および注文情報

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

8.3.4 Current Regulation

The current through the motor windings is regulated by an adjustable fixed-off-time PWM current regulation circuit. When an H-bridge is enabled, current rises through the winding at a rate dependent on the DC voltage, inductance of the winding, and the magnitude of the back EMF present. Once the current hits the current chopping threshold, the bridge enters a decay mode for a fixed, 20 μs, period of time to decrease the current. After the off time expires, the bridge is re-enabled, starting another PWM cycle.

DRV8885 current_reg_lvsd39.gifFigure 14. Current Chopping Waveform

The PWM chopping current is set by a comparator which looks at the voltage across current sense FETs in parallel with the low-side drivers. The current sense FETs are biased with a reference current that is the output of a current-mode sine-weighted DAC whose full-scale reference current is set by the current through the RREF pin. An external resistor is placed from the RREF pin to GND in order to set the reference current. In addition, the TRQ pin can further scale the reference current.

The chopping current is calculated as follows:

Equation 1. DRV8885 eq_chop_current_lvsd39.gif

Example: If a 30-kΩ resistor is connected to the RREF pin, the chopping current will be 1 A (TRQ at 100%)

The TRQ pin is the input to a DAC used to scale the output current. The current scalar value for different inputs is shown below.

Table 5. Torque DAC Settings

TRQ CURRENT SCALAR (TRQ)
0 100%
Z 75%
1 50%