MIC2208_10 Datasheet, PDF (11/18 Pages) Micrel Semiconductor – 3mm x 3mm 1MHz 3A PWM Buck Regulator

Micrel, Inc.
(P_L) can be calculated by multiplying the DC resistance
(DCR) times the square of the output current:
P_L = DCR × I_OUT2
Also, be aware that there are additional core losses
associated with switching current in an inductor. Since
most inductor manufacturers do not give data on the
type of material used, approximating core losses
becomes very difficult, so verify inductor temperature
rise.
Switching losses occur twice each cycle, when the
switch turns on and when the switch turns off. This is
caused by a non-ideal world where switching transitions
are not instantaneous, and neither are currents. Figure 6
demonstrates (Or exaggerates.) how switching losses
due to the transitions dissipate power in the switch.
MIC2208
Normally, when the switch is on, the voltage across the
switch is low (virtually zero) and the current through the
switch is high. This equates to low power dissipation.
When the switch is off, voltage across the switch is high
and the current is zero, again with power dissipation
being low. During the transitions, the voltage across the
switch (V_S-D) and the current through the switch (I_S-D) are
at middle, causing the transition to be the highest
instantaneous power point. During continuous mode,
these losses are the highest. Also, with higher load
currents, these losses are higher. For discontinuous
operation, the transition losses only occur during the “off”
transition since the “on” transitions there is no current
flow through the inductor.
Figure 6. Switching Transition Losses
May 2010
11
M9999-051410-D