ZHCSPH2 January   2022 DRV8251A

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and 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 Typical Characteristics
    7. 7.7 Timing Diagrams
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 External Components
    4. 8.4 Feature Description
      1. 8.4.1 Bridge Control
      2. 8.4.2 Current Sense and Regulation (IPROPI)
        1. 8.4.2.1 Current Sensing
        2. 8.4.2.2 Current Regulation
      3. 8.4.3 Protection Circuits
        1. 8.4.3.1 Overcurrent Protection (OCP)
        2. 8.4.3.2 Thermal Shutdown (TSD)
        3. 8.4.3.3 VM Undervoltage Lockout (UVLO)
    5. 8.5 Device Functional Modes
      1. 8.5.1 Active Mode
      2. 8.5.2 Low-Power Sleep Mode
      3. 8.5.3 Fault Mode
    6. 8.6 Pin Diagrams
      1. 8.6.1 Logic-Level Inputs
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Brush DC Motor
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Motor Voltage
          2. 9.2.1.2.2 Motor Current
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Stall Detection
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1 Stall Detection Timing
          2. 9.2.2.2.2 Stall Threshold Selection
        3. 9.2.2.3 Application Curves
      3. 9.2.3 Relay Driving
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
          1. 9.2.3.2.1 Control Interface for Single-Coil Relays
          2. 9.2.3.2.2 Control Interface for Dual-Coil Relays
        3. 9.2.3.3 Application Curves
      4. 9.2.4 Multi-Sourcing with Standard Motor Driver Pinout
    3. 9.3 Current Capability and Thermal Performance
      1. 9.3.1 Power Dissipation and Output Current Capability
      2. 9.3.2 Thermal Performance
        1. 9.3.2.1 Steady-State Thermal Performance
        2. 9.3.2.2 Transient Thermal Performance
  10. 10Power Supply Recommendations
    1. 10.1 Bulk Capacitance
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
  13. 13Mechanical, Packaging, and Orderable Information

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8.4.2.2 Current Regulation

The DRV8251A device integrates current regulation using a fixed off-time current chopping scheme. This allows the devices to limit the output current in case of motor stall, high torque, or other high current load events without involvement from the external controller as shown in Figure 8-5.

GUID-20210830-SS0I-JFJP-NVN7-WT4HZGVK9C0G-low.svg Figure 8-5 Off-Time Current-Regulation

The current chopping threshold (ITRIP) is set through a combination of the VREF voltage (VVREF) and IPROPI output resistor (RIPROPI). This is done by comparing the voltage drop across the external RIPROPI resistor to VVREF with an internal comparator.

Equation 3. ITRIP (A) x AIPROPI (μA/A) = VVREF (V) / RIPROPI (Ω)

For example, if VVREF = 3.3 V, RIPROPI = 1310 Ω, and AIPROPI = 1575 μA/A, then ITRIP will be approximately 1.6 A.

The fixed off-time current chopping scheme supports up to 100% duty cycle current regulation since the H-bridge automatically enables after the tOFF period and does not require a new control input edge on the INx pins to reset the outputs. When the motor current exceeds the ITRIP threshold, the outputs will enter a current chopping mode with a fixed off time (tOFF). During tOFF, the H-bridge enters a brake/low-side slow decay state (both low-side MOSFETs ON) for tOFF duration after IOUT exceeds ITRIP. After tOFF, the outputs re-enable according to the control inputs if IOUT is less than ITRIP. If IOUT is still greater than ITRIP, the H-bridge enters another period of brake/low-side slow decay for tOFF. If the state of the INx control pins changes during the tOFF time, the remainder of the tOFF time is ignored, and the outputs will again follow the inputs.

The ITRIP comparator has both a blanking time (tBLK) and a deglitch time (tDEG). The internal blanking time helps to prevent voltage and current transients during output switching from effecting the current regulation. These transients may be caused by a capacitor inside the motor or on the connections to the motor terminals. The internal deglitch time ensures that transient conditions do not prematurely trigger the current regulation. In certain cases where the transient conditions are longer than the deglitch time, placing a 10-nF capacitor on the IPROPI pin, close to the device, will help filter the transients on IPROPI output so current regulation does not prematurely trigger. The capacitor value can be adjusted as needed, however large capacitor values may slow down the response time of the current regulation circuitry.

The internal current regulation and current feedback can be disabled by tying IPROPI to GND and setting the VREF pin voltage greater than GND. If current feedback is required and current regulation is not required, set VVREF and RIPROPI such that VIPROPI never reaches the VVREF threshold. For proper operation of the current regulation circuit, VVREF must be within the range of the VREF pin voltages specified in the Recommended Operating Conditions table.