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

3.1.1 How Gate Current Causes Damage

Unfortunately, there are adverse effects of a high slew rate in a high-power system. The inherent capacitive coupling of the MOSFET, and the effects of parasitic LC resonance increase as more current flows through the FETs and the VDS voltage transitions more quickly.

Figure 3-1 Inductive Spiking and Coupling From Switching on MOSFET

As shown in Figure 3-1, the high-frequency component of the rising edge of the gate signal—and more importantly, the rising VDS signal going through the Miller region—causes current to flow onto the intrinsic capacitors of the other FET. This signal couples through the inherent gate-to-drain or gate-to-source capacitor because capacitors have lower impedance at higher frequencies. If these coupled signals are high enough, they can exceed absolute maximum ratings of the motor driver or turn on the low- and high-side FETs within one phase to cause a shoot-through condition as current bypasses the motor and flows through the direct path from VDRAIN to GND.

MOSFETs have a limit of maximum slew rate before they turn on due to CGD coupling. This means that if the slew rate is too high—even if the gate is shorted directly to the source—the MOSFET turns on. When considering the gate driver pulldown strength and parasitic inductance on the gate path, this reduces the maximum slew rate possible before causing unintentional turn-on.

Simply put, higher gate current means more coupling, and less gate current means less coupling.

To reiterate:

  • Too much gate current leads to damage
  • Decreasing the current prevents damage
  • Choosing the right gate drive current (IDRIVE) for the system is essential.

Now that the effects of too much gate current are understood, methods to adjust the gate current must be developed and calculation of a gate current for a given system must be derived.