SLUAAX9 June   2025 BQ25756

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2MOSFET Power Losses in Buck and Boost Chargers
    1. 2.1 Buck Mode Losses
    2. 2.2 Boost Mode Losses
    3. 2.3 Closing Thoughts for FET Losses
  6. 3Evaluating MOSFETs Using the Design Calculator
    1. 3.1 Correlating MOSFET Data Sheet Parameters With the Design Calculator Parameters
    2. 3.2 Design Calculator MOSFET Comparison Example
  7. 4BOM Evaluation
  8. 5Summary
  9. 6References

3.2 Design Calculator MOSFET Comparison Example

As an example, the design calculator is used here to compare the TI recommended MOSFET, the SiR680LDP, and the SiR880BDP as the custom MOSFET. For this example, the following operating conditions are used for both.

All other input parameters are left as the default.

Table 3-1 Operating Conditions for Design Calculator Example
Parameter Value
VIN (minimum) 5V
VIN (nominal) 10V
VIN (maximum) 50V
VBAT 21V
Vext_drv 10V
Iout 8A
fsw 200kHz
Rfsw 200kΩ
ISAT 19A
Selected Inductance, L 10μH
Selected Inductor DCR 12mΩ

These operating conditions then result in the following efficiency and power loss graphs.

After the yellow cells are filled in, the calculator can plot these graphs. Plot 1 is the recommendation, SiR680LDP, and plot 2 is SiR880BDP.

Design Calculator Efficiency and Loss Graphs for MOSFET Comparison Figure 3-3 Design Calculator Efficiency and Loss Graphs for MOSFET Comparison

In this example, the SiR880BDP MOSFET (depicted in Plot 2) has a higher efficiency for a lighter load because of the lower gate capacitance and output capacitance. The lower capacitance reduces the switching losses. At higher loads, the conduction losses become greater than the switching losses and the SiR680LDP is more efficient because of the lower RDS(ON).