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 MOSFET Gate Current

As previously mentioned, the MOSFET drain and gate current is the backbone of power delivery to the motor. To deliver current and turn the FET on, charge must build up on the intrinsic gate capacitors of the MOSFET. This process is explained in more detail in the Fundamentals of MOSFET and IGBT Gate Driver Circuits and Understanding Smart Gate Drive application notes.

As a result, link the rate of electrical charge, or current, at the gate-to-the rise in drain-to-source voltage of the FET, as shown in the ideal first-order Equation 1:

Equation 1. S R D S =   I D R I V E × V D S Q g d

Where:

  • SRDS = slew rate of the drain to source voltage, in seconds
  • IDRIVE = current sourced to or sunk out of the gate, in amps
  • VDS = voltage difference between the MOSFET drain voltage and source, in volts
  • Qgd = inherent gate-to-drain charge for the MOSFET, in coulombs

According to Equation 1, a high IDRIVE and a small Qgd results in a very fast slew rate, as VDRAIN is usually fixed in a system unless the system supply voltage is specifically designed to change. Since a high slew rate results in lower switching losses in the MOSFETs it can seem at first beneficial to make the slew rate as high as possible. However, most designers try to use a higher slew rate without realizing that there are adverse effects of using a slew rate that is too high for the design.