SLVAFV2 June   2024 LMR51610 , TPS629210

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Estimate and Measure the Voltage Drop in Buck Converter
    1. 2.1 Estimation of Voltage Drop in Buck Converter Working in CCM
    2. 2.2 Measurement of Voltage Drop of Buck Converter
  6. 3Voltage Drop Comparison Between Calculation, Simulation, and Measurement
  7. 4Summary
  8. 5References

4 Summary

This application note provides a mathematical method for calculating the theoretical voltage drop in the buck converter. The simulation model and practical tests in TPS629210 and LMR51610 were used to verify this theory. The calculation and simulation results showed a high degree of consistency. In practice, the temperature offset of the FETs introduces a certain level of nonlinearity. The calculation results are highly accurate once we add the influence of the temperature in the FETs.

Therefore, based on the above theoretical analysis, simulation and test results. This application note provides an easy way to calculate the voltage drop and how to select proper devices to fully utilize the battery.

  • Devices with low Rdson

From Equation 4, the main contributor to the voltage drop is the Rdsonof the FETs. In addition, when devices operate in the dropout zone, the duty cycle always increases to the upper limit of the duty cycle. Therefore, the Rdson of the low-side FETS is negligible, and we need to choose a device with a lower Rdson of the high-side FETs to decrease the voltage drop as much as possible.

  • Devices with 100% duty cycle control mode

To further decrease the voltage drop in dropout zone, we can select a device with 100% duty cycle function. A 100% duty cycle indicates direct conduction from the input to the output. This eliminated the influence of the duty cycle.