SLVSFU6 January   2022 DRV8251A

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  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

Package Options

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

8.4.2.1 Current Sensing

The IPROPI pin outputs an analog current proportional to the current flowing through the low-side power MOSFETs in the H-bridge scaled by AIPROPI. The IPROPI output current can be calculated by Equation 1. The ILSx in Equation 1 is only valid when the current flows from drain to source in the low-side MOSFET. If current flows from source to drain or through the body diode, the value of ILSx for that channel is zero. For instance, if the bridge is in the brake, slow-decay state, then the current out of IPROPI is only proportional to the current in one of the low-side MOSFETs.

Equation 1. IPROPI (μA) = (ILS1 + ILS2) (A) x AIPROPI (μA/A)

The AERR parameter in the Electrical Characteristics table is the error associated with the AIPROPI gain. It indicates the combined effect of offset error added to the IOUT current and gain error.

The motor current is measured by an internal current mirror architecture on the low-side FETs which removes the need for an external power sense resistor as shown in Figure 8-4. The current mirror architecture allows for the motor winding current to be sensed in both the drive and brake low-side slow-decay periods allowing for continuous current monitoring in typical bidirectional brushed DC motor applications. In coast mode, the current is freewheeling and cannot be sensed because it flows from source to drain. However, the current can be sampled by briefly reenabling the driver in either drive or slow-decay modes and measuring the current before switching back to coast mode again.

GUID-B7C98B8D-FADE-4EEE-9952-E47D2EBAD287-low.gif Figure 8-4 Integrated Current Sensing

The IPROPI pin should be connected to an external resistor (RIPROPI) to ground in order to generate a proportional voltage (VIPROPI) on the IPROPI pin with the IIPROPI analog current output. This allows for the load current to be measured as the voltage drop across the RIPROPI resistor with a standard analog to digital converter (ADC). The RIPROPI resistor can be sized based on the expected load current in the application so that the full range of the controller ADC is utilized. Additionally, the DRV8251A device implements an internal IPROPI voltage clamp circuit to limit VIPROPI with respect to VVREF on the VREF pin and protect the external ADC in case of output overcurrent or unexpected high current events.

The corresponding IPROPI voltage to the output current can be calculated by Equation 2.

Equation 2. VIPROPI (V) = IPROPI (A) x RIPROPI (Ω)

The IPROPI output bandwidth is limited by the sense delay time (tDELAY) of the internal current sensing circuit. This time is the delay from the low-side MOSFET enable command (from the INx pins) to the IPROPI output being ready.

If the device is alternating between drive and slow-decay (brake) in an H-bridge PWM pattern then the low-side MOSFET sensing the current is continuously on and the sense delay time has no impact to the IPROPI output. If a command on the INx pins disables the low-side MOSFETs (according to the logic tables in Section 8.4.1), the IPROPI output will disable with the input logic signal. Although the low-side MOSFETs may still conduct current as they disable according to the device slew rate (noted in the Electrical Characteristics table by tRISE time), IPROPI will not represent the current in the low-side MOSFETs during this turnoff time.