SLVSD29 October   2015 DRV8704

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 SPI Timing Requirements
    7. 6.7 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  Direct PWM Input Mode (Dual Brushed DC Gate Driver)
      3. 7.3.3  Current Regulation
      4. 7.3.4  Decay Modes
      5. 7.3.5  Blanking Time
      6. 7.3.6  Gate Drivers
      7. 7.3.7  Configuring Gate Drivers
      8. 7.3.8  External FET Selection
      9. 7.3.9  Protection Circuits
        1. 7.3.9.1 Overcurrent Protection (OCP)
        2. 7.3.9.2 Gate Driver Fault (PDF)
        3. 7.3.9.3 Thermal Shutdown (TSD)
        4. 7.3.9.4 Undervoltage Lockout (UVLO)
      10. 7.3.10 Serial Data Format
    4. 7.4 Device Functional Modes
    5. 7.5 Register Maps
      1. 7.5.1 Control Registers
        1. 7.5.1.1 CTRL Register (Address = 0x00h)
          1. Table 4. CTRL Register
        2. 7.5.1.2 TORQUE Register (Address = 0x01h)
          1. Table 5. TORQUE Register
        3. 7.5.1.3 OFF Register (Address = 0x02h)
          1. Table 6. OFF Register
        4. 7.5.1.4 BLANK Register (Address = 0x03h)
          1. Table 7. BLANK Register
        5. 7.5.1.5 DECAY Register (Address = 0x04h)
          1. Table 8. DECAY Register
        6. 7.5.1.6 Reserved Register Address = 0x05h
          1. Table 9. Reserved Register
        7. 7.5.1.7 DRIVE Register Address = 0x06h
          1. Table 10. DRIVE Register
        8. 7.5.1.8 STATUS Register (Address = 0x07h)
          1. Table 11. STATUS Register
  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 External FET Selection
        2. 8.2.2.2 IDRIVE Configuration
        3. 8.2.2.3 Current Chopping Configuration
        4. 8.2.2.4 Decay Modes
        5. 8.2.2.5 Sense Resistor
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Bulk Capacitance
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  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

7.3.3 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 and inductance of the winding and the magnitude of the back EMF present. Once the current hits the current chopping threshold, the bridge disables the current for a fixed period of time, which is programmable between 525 ns and 128 µs by writing to the TOFF bits in the OFF register. After the off time expires, the bridge is re-enabled, starting another PWM cycle.

Note that the decay mode is set by DECMOD bits in the DECAY register. Slow, fast, mixed, or auto mixed decay modes are available.

The chopping current is set by a comparator which compares the voltage across a current sense resistor connected to the xISENx pins, multiplied by the gain of the current sense amplifier, with a reference voltage. The current sense amplifier is programmable in the CTRL register.

When driving in PWM mode, the chopping current is calculated as follows:

Equation 1. DRV8704 eq_01_Ichop_lvsd29.gif

where

  • TORQUE is the setting of the TORQUE bits
  • ISGAIN is the programmed gain of the ISENSE amplifiers (5, 10, 20, or 40).