STD70N03L Datasheet, PDF (9/16 Pages) STMicroelectronics – N-channel 30V - 0.0059ohm - 70A - DPAK / IPAK STripFET TM III Power MOSFET

STD70N03L - STD70N03L-1
Appendix A Power losses estimation
Power losses estimation
Figure 19. Buck converter
The power losses associated with the FETs in a synchronous buck converter can
be estimated using the equations shown in the table below. The formulas give a
good approximation, for the sake of performance comparison, of how different
pairs of devices affect the converter efficiency. However a very important
parameter, the wotking temperature, is not considered. The real device behavior is
really dependent on how the heat generated inside the devices is removed to allow
for a safer working junction temperature.
The low side (SW2) device requires:
● Very low R_DS(on) to reduce conduction losses
● Small Q_gls to reduce the gate charge losses
● Small C_oss to reduce losses due to output capacitance
● Small Q_rr to reduce losses on SW₁ during its turn-on
● The C_gd/C_gs ratio lower than V_th/V_gg ratio especially with low drain to source
voltage to avoid the cross conduction phenomenon.
The high side (SW1) device requires:
● Small Rg and Lg to allow higher gate current peak and to limit the voltage
feedback on the gate
● Small Q_g to have a faster commutation and to reduce gate charge losses
● Low R_DS(on) to reduce the conduction losses
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