SLVAFS9 August   2024 DRV8316 , DRV8317

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Power Loss and Performance Expectations
  6. 3Lab Data and Analysis
    1. 3.1 Current Output, Rds(on), and PWM Frequency
    2. 3.2 Slew Rate and Device
    3. 3.3 Temporal Thermal Analysis
    4. 3.4 PCB Design
  7. 4Thermal Design Recommendations
  8. 5Summary
  9. 6References

3.2 Slew Rate and Device

The slew rate of the voltage switching on the output phases of the device can also affect the contribution of switching losses to the overall power loss of the system. The expectation is that, given a constant current output and PWM frequency, a faster slew rate reduces the switching loss, and the device runs at a cooler temperature than with a slower slew rate. This is shown in Table 3-2. Note that voltage is roughly 17.414 to 17.416V in all tests, the motor was characterized while loaded, and the package temperature was measured 2 minutes after the target output current of around 3A RMS was achieved.

Table 3-2 DRV8316 Results: Fixed PWM While Increasing Slew Rate
PWM Frequency

(kHz)

 Output Current RMS (A) Slew Rate

(V/μs)

 Package Temperature (°C, DRV8316)
20 3.00 25 108

20

 2.95 50 82.4

20

 2.98 125 68.6

20

 2.95 200 66.2
Table 3-3 DRV8317 Results: Fixed PWM While Increasing Slew Rate
PWM Frequency

(kHz)

 Output Current RMS (A) Slew Rate

(V/μs)

 Package Temperature (°C, DRV8317)
20 1.98 25 112.3

20

 1.98 50 85.5

20

 1.98 125 70.4

20

 1.98 200 65.5

Sensorless Field Oriented Control (FOC) was used to drive the motor during the above experiment. As expected, the temperature of the device package decreased as the slew rate increased. However, while an even higher slew rate can be expected to further decrease the switching losses, designers must also keep in mind that other issues can occur. High slew rates can cause unwanted half-bridge shoot-through events through dV/dt coupling, as well as poor EMI performance through node ringing during switching. All of these drawbacks must also be considered when choosing the right slew rate for the application.

Additionally, see how the DRV8316 performs compared to the DRV8317. The DRV8316 has a lower Rds(on) value than the DRV8317, so we expect the DRV8316 to have lower conduction loss. Although the above experiment shows the DRV8316 running at around 3A RMS while the DRV8317 runs at about 2A RMS, the DRV8316 is cooler at each slew rate except 200V/μs (although the difference can be attributed to measurement error). Despite the significant difference in current output, the driver with the smaller Rds(on) ran cooler than the alternative, which shows how much conduction loss contributes to the overall temperature of the device. Note, however, that these two devices are meant for different applications. When comparing the thermal performance between two devices, designers need to consider motor drivers with similar operating power and recommended end uses. The DRV8316 is designed to be used in slightly higher-power applications than the 8317 for this reason.