SLVAFZ3 December   2024 DRV8161 , DRV8162 , DRV8350 , DRV8350F , DRV8353 , DRV8353F

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2System Power Requirements
  6. 3Motor Current and MOSFET Selection
    1. 3.1 How Does a BLDC Motor Driver System Work?
    2. 3.2 Motor Current and QG Value Relation
    3. 3.3 Role of a Motor Driver
    4. 3.4 Can my MOSFET be Driven or Commutated?
      1. 3.4.1 Example 1 – Medium Power (4.8kW – 48V × 100A)
      2. 3.4.2 Example 2 – High Power (19.2kW – 48V × 400A)
  7. 4Motor Driver Specifications to Consider
    1. 4.1 DRV8353 - Internally Generated Gate Drive Supply
    2. 4.2 DRV8161/DRV8162 – Externally Generated Gate Drive Supply
  8. 5Advantages of TI’s BLDC Drivers With Smart Gate Drive
  9. 6Maximum Source and Sink Current and QGD
  10. 7Older Designs
  11. 8Summary
  12. 9References

5 Advantages of TI’s BLDC Drivers With Smart Gate Drive

A key consideration when driving a MOSFET is determining how fast the gates can be charged as it determines the MOSFET’s slew time. The charge needed by the MOSFET to connect the drain voltage to the source, and the rate at which the driver is configured to deliver that charge, determines the VDS (Voltage Drain to Source) slew rate. The VDS slew happens during the QGD portion of the MOSFET gate charge. Figure 5-1 shows the different charging regions of the MOSFET. By increasing the gate current, the MOSFET is able to turn on and off faster, decreasing the switching losses of the MOSFET.

MOSFET Turn-on ResponseFigure 5-1 MOSFET Turn-on Response

TI’s Smart Gate Drive (SGD) technology allows the user to select the peak gate drive current needed to turn-on/turn-off the MOSFET. For more information on SGD please check out Understanding Smart Gate Drive application note.

Most of TI’s BLDC drivers offer a peak source/sink gate current of 1A/2A respectively. The SGD offers numerous levels of adjustment to the gate current allowing the driver to adjust the VDS slew rate and allow the driver to work with various sized MOSFETs.

Equation 4 shows how to calculate peak gate current needed for desired slew times.

Equation 4. Tturn-on/turn-off=MOSFET QGDIsource/sink

Table 5-1 calculates the peak gate current needed to achieve desired slew rates for the MOSFETs described in earlier examples. Using SGD, the user is able to choose a current level closest to the desired slew rate.

Table 5-1 Gate Current and Slew time calculation

Example MOSFET

Gate-Drain

Charge

Turn

On Time

Turn

Off Time

Source

Current

Sink

Current

MOSFET AQGD (nC)Turn on (ns)Turn off (ns)Isource (mA)Isink (mA)
3010050300.0600.0
200100150.0300.0
300150100.0200.0
40020075.0150.0
MOSFET BQGD (nC)Turn on (ns)Turn off (ns)Isource (mA)Isink (mA)
4010050400.0800.0
200100200.0400.0
300150133.3266.7
400200100.0200.0
Note: Generally, the turn off time is selected to be faster than the turn on time.