SLVAF66 June   2021 DRV3255-Q1 , DRV8300 , DRV8301 , DRV8302 , DRV8303 , DRV8304 , DRV8305 , DRV8305-Q1 , DRV8306 , DRV8307 , DRV8308 , DRV8320 , DRV8320R , DRV8323 , DRV8323R , DRV8340-Q1 , DRV8343-Q1 , DRV8350 , DRV8350F , DRV8350R , DRV8353 , DRV8353F , DRV8353R

 

  1. 1 Introduction to High-Power Motor Applications
    1. 1.1 Effects of a Poorly-Designed High-Power Motor Driver System
    2. 1.2 Example of the High-Power Design Process
  2. 2 Examining a High-Power Motor Drive System at a High Level
    1. 2.1 Anatomy of the Motor Drive Power Stage and How to Troubleshoot
    2. 2.2 Troubleshooting a High-Power System
  3. 3 High-Power Design Through MOSFETs and MOSFET Gate Current (IDRIVE)
    1. 3.1 MOSFET Gate Current
      1. 3.1.1 How Gate Current Causes Damage
      2. 3.1.2 Gate Resistors and Smart Gate Drive Technology
        1. 3.1.2.1 Gate Resistors
        2. 3.1.2.2 Smart Gate Drive and Internally-Controlled Sink and Source Gate Currents
        3. 3.1.2.3 Summary for Gate Resistors and Smart Gate Drive Technology
      3. 3.1.3 Example Gate Current Calculation for a Given FET
  4. 4 High-Power Design Through External Components
    1. 4.1 Bulk and Decoupling Capacitors
      1. 4.1.1 Note on Capacitor Voltage Ratings
    2. 4.2 RC Snubber Circuits
    3. 4.3 High-Side Drain to Low-Side Source Capacitor
    4. 4.4 Gate-to-GND Diodes
  5. 5 High-Power Design Through a Parallel MOSFET Power Stage
  6. 6 High-Power Design Through Protection
    1. 6.1 VDS and VGS Monitoring
      1. 6.1.1 Turning Off the FETs During an Overcurrent, Shoot-Through, or FET Shorting Event
    2. 6.2 Passive Gate-to-Source Pulldown Resistors
    3. 6.3 Power Supply Reverse Polarity or Power Supply Cutoff Protection
  7. 7 High-Power Design Through Motor Control Methods
    1. 7.1 Brake versus Coast
      1. 7.1.1 Algorithm-Based Solutions
      2. 7.1.2 External Circuit Solutions
      3. 7.1.3 Summary of Brake versus Coast
  8. 8 High-Power Design Through Layout
    1. 8.1 What is a Kelvin Connection?
    2. 8.2 General Layout Advice
  9. 9 Conclusion
  10. 10Acknowledgments

4.2 RC Snubber Circuits

Figure 4-3 Example RC Snubbers

The snubber circuit is not only used in motor driver applications but is also used in a lot of switching regulator circuits. As a result, there are a lot of resources that have covered this subject.

For an introduction, the RC snubber consists of a resistor and capacitor connected in series from the switch node to a constant voltage reference, such as a GND connection. For a motor drive circuit, place an RC snubber between the phase node and the high-side drain of the FET, and between the phase node and the low-side source of the FET shown in Figure 4-3.

They are most effective reducing phase oscillations, or voltage ringing across each MOSFET. They reduce the initial spike at a node and provide a dampening factor to reduce the number of ringing cycles.

However, the values of RC must be tuned for the parasitics of a particular system. Unless the parasitics can be modeled, the R and C values are chosen experimentally. Luckily, there are many resources explaining how to calculate them, such as the E2E FAQ for Proper RC Snubber Design for Motor Drivers as an example.

In summary:

  • RC snubbers are very good at reducing the settling time of a ringing node
  • Optimal RC snubber values depend on the parasitic values of a given system
  • Place snubbers very close to the MOSFET, on the same layer
    • If placed on opposite layers of the FET, the via inductance reduces the effectiveness of the snubber