SLVAF76 August   2021 TPS62901 , TPS62902 , TPS62902-Q1 , TPS62903 , TPS62903-Q1

 

  1.   Trademarks
  2. 1Applications With Limited Area
    1. 1.1 Best TPS62903 Configuration to Reduce Size
    2. 1.2 Design Example
  3. 2Applications With High Efficiency and Thermal Requirement
    1. 2.1 Conduction Losses in the MOSFET
    2. 2.2 Conduction Losses in the Inductor
    3. 2.3 Switching Losses in the MOSFET
    4. 2.4 Losses in the Input and Output Capacitors
    5. 2.5 Analysis and Recommendations
  4. 3Conclusion

2.1 Conduction Losses in the MOSFET

The conduction loss in the MOSFET inside the buck converter is the power loss due to the on-resistance (RDS(ON)) of the high-side FET and low-side FET as they conduct current. As the high-side FET is on and the low-side FET is off, the conduction loss of the high-side FET can be estimated from the output current, on-resistance, and on-duty cycle (D). As the high-side FET is off and the low-side FET is on, the conduction loss of the low-side FET can be estimated from the output current, on-resistance, and off-duty cycle (1-D). Use Equation 1 and Equation 2 to estimate the power loss on both the high-side and low-side FETs. Equation 1 and Equation 2 provide a good estimate of the FET conduction power losses and how the RDS(ON) contributes to efficiency:

Equation 1. C o n d u c t i o n _ L o s s _ H _ F E T = I O U T _ r m s 2   ×   R D S O N _ H × D
Equation 2. Conduction_Loss_L_FET=IOUT_rms2 × RDSON_L×(1-D)

D is duty cycle and can be calculated as VOUT/VIN. Choosing a converter that has low RDS(ON) is key to improve efficiency of the system. The TPS62903 has very low RDS(ON), the high-side FET on resistance is 62 mΩ and the low-side FET on resistance is only 22 mΩ. This helps on the reducing the conduction loss.