SLVSHI4A October   2025  – December 2025 DRV81545

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specification
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Integrated Clamp Diode, VCLAMP
      2. 6.3.2 Protection Circuits
        1. 6.3.2.1 ILIM Analog Current Limit
          1. 6.3.2.1.1 Effect of Load Resistance on Power Dissipation Before TSD
        2. 6.3.2.2 Cut-Off Delay (COD)
        3. 6.3.2.3 Thermal Shutdown (TSD)
        4. 6.3.2.4 Undervoltage Lockout (UVLO)
      3. 6.3.3 Fault Conditions Summary
    4. 6.4 Device Functional Modes
      1. 6.4.1 Hardware Interface Operation
      2. 6.4.2 Parallel Outputs
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 External Components
      2. 7.2.2 Continuous Current Capability
      3. 7.2.3 Power Dissipation
      4. 7.2.4 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Bulk Capacitance
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.3.1 Bulk Capacitance

Appropriate local bulk capacitance is an important factor in motor drive system design. Having more bulk capacitance is generally beneficial, although the disadvantages include increased cost and physical size. Bulk capacitors near the motor driver act as a local reservoir of electrical charge to smooth out the motor current variation.

Experienced engineers often use general guidelines about bulk capacitance to select the capacitor values. One such guideline says to use at least 1μF to 4μF of capacitance for each Watt of load power. For example, a solenoid which draws 4 Amps from a 24V supply has a power of 96 Watts, leading to bulk capacitance of 96μF to 384μF, using this general guideline.

The voltage rating for bulk capacitors must be higher than the operating voltage, to provide margin for cases when the motor transfers energy to the supply.

A large value of bulk capacitance is desired to provide a constant VM supply voltage during current transitions, such as solenoid start-up, changes in load torque, or PWM operation. A working estimate of the required capacitance for consistent supply is essential to reduce complexity, cost and size of board electronics. We can use a general guideline method to find an appropriate capacitor size based on the expected load current variation and allowable motor supply voltage variation:

Equation 15. C B U L K > k × ∆ I M O T O R × T P W M ÷ ∆ V S U P P L Y

Where:

CBULK is the bulk capacitance

k is a scale factor to account for the ESR for typical capacitors in this type of application; k ≈ 3 is practical for these cases.

ΔIMOTOR is the expected variation in motor current, imax – imin

TPWM is the PWM period which is the reciprocal of the PWM frequency

ΔVSUPPLY is the allowable variation in the motor supply voltage.

Figure 7-4 plots several data points and applies this general guideline, showing relatively good agreement.

DRV81545 Measured Results and 3 × General Guideline, Accounting for Real-World Non-Zero ESR Values of Electrolytic Capacitors Figure 7-4 Measured Results and 3 × General Guideline, Accounting for Real-World Non-Zero ESR Values of Electrolytic Capacitors

See also the Bulk Capacitor Sizing for DC Motor Drive Applications application note.