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

9.3.1 Power Dissipation and Output Current Capability

Total power dissipation for the device consists of three main components: quiescent supply current dissipation (PVM), the power MOSFET switching losses (PSW), and the power MOSFET RDS(on) (conduction) losses (PRDS). While other factors may contribute additional power losses, they are typically insignificant compared to the three main items.

Equation 4. PTOT = PVM + PSW + PRDS

PVM can be calculated from the nominal motor supply voltage (VVM) and the IVM active mode current specification.

Equation 5. PVM = VVM x IVM
Equation 6. PVM = 96 mW = 24 V x 4 mA

PSW can be calculated from the nominal motor supply voltage (VVM), average output current (IAVG), switching frequency (fPWM) and the device output rise (tRISE) and fall (tFALL) time specifications.

Equation 7. PSW = PSW_RISE + PSW_FALL
Equation 8. PSW_RISE = 0.5 x VM x IAVG x tRISE x fPWM
Equation 9. PSW_FALL = 0.5 x VM x IAVG x tFALL x fPWM
Equation 10. PSW_RISE = 26.4 mW = 0.5 x 24 V x 0.5 A x 220 ns x 20 kHz
Equation 11. PSW_FALL = 26.4 mW = 0.5 x 24 V x 0.5 A x 220 ns x 20 kHz
Equation 12. PSW = 53 mW = 26.4 mW + 26.4 mW

PRDS can be calculated from the device RDS(on) and average output current (IAVG).

Equation 13. PRDS = IAVG2 x (RDS(ON)_HS + RDS(ON)_LS)

RDS(ON) has a strong correlation with the device temperature. Assuming a device junction temperature of 85 °C, RDS(on) could increase ~1.5x based on the normalized temperature data. The calculation below shows this derating factor. Alternatively, Section 7.6 shows curves that plot how RDS(on) changes with temperature.

Equation 14. PRDS = 169 mW = (0.5 A)2 x (225 mΩ x 1.5 + 225 mΩ x 1.5)

Based on the example calculations above, the expressions below calculate the total expected power dissipation for the device.

Equation 15. PTOT = PVM + PSW + PRDS
Equation 16. PTOT = 318 mW = 96 mW + 53 mW + 169 mW

The driver's junction temperature can be estimated using PTOT, device ambient temperature (TA), and package thermal resistance (RθJA). The value for RθJA depends heavily on the PCB design and copper heat sinking around the device. Section 9.3.2 describes this dependence in greater detail.

Equation 17. TJ = (PTOT x RθJA) + TA
Equation 18. TJ = 98 °C = (0.318 W x 40.4 °C/W) + 85°C

The device junction temperature should remain below its absolute maximum rating for all system operating conditions. The calculations in this section provide reasonable estimates for junction temperature. However, other methods based on temperature measurements taken during system operation are more realistic and reliable. Additional information on motor driver current ratings and power dissipation can be found in Section 9.3.2 and Section 12.1.1.