SDAA218 November   2025 DRV8363-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Power Loss and Thermals in Motor Driver Systems
    1. 2.1 Conduction Losses
    2. 2.2 Switching Losses
      1. 2.2.1 Effect of Switching Frequency
  6. 3Real World Motor Driver Limitation
    1. 3.1 Electro-Magnetic Interference (EMI) – System Noise Considerations
    2. 3.2 Motor Driver Voltage Tolerance
  7. 4Summary
  8. 5References

2.1 Conduction Losses

Conduction losses in MOSFETs occur when current conducts from drain to source. The channel resistance of the MOSFET while conducting, is commonly referred to as on-state resistance, or Rds(on). These losses scale with the square of the current, so motor current becomes the dominating factor in determining conduction losses. Conduction losses during FOC commutation are calculated using the formula:

Equation 1. P c o n d u c t i o n   =   3   ×   I R M S 2   ×   R d s ( o n )

Example 1

Assume two systems with total power of 960W.

System A = 12V Battery

System B = 48V Battery

Equation 2. P   =   I   ×   V

Based on Equation 2, if the same desired power output for both the 12V and 48V system is assumed, using Ohm's law we can deduce that the 48V system operates with four times less current. Therefore, less current will pass through the MOSFETs, resulting in 16 times less conduction losses in the 48V system based on Equation 1. Figure 2-1 illustrates the losses shown in Example 1.

Conduction Losses 12V vs 48V Figure 2-1 Conduction Losses 12V vs 48V