mic4720yml Micrel Semiconductor, mic4720yml Datasheet - Page 12

• Manufacturer Part Number: mic4720yml
• Description: Mic4720 3mm X 3mm 2.0mhz 2a Integrated Switch Buck Regulator
• Manufacturer: Micrel Semiconductor

determines whether the dominant factor in conduction
losses will be the internal MOSFET or the Schottky
diode. Higher duty cycles place the power losses on the
high side switch, and lower duty cycles place the power
losses on the Schottky diode.
Inductor conduction losses (P
multiplying the DC resistance (DCR) times the square of
the output current;
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
transitions dissipate power in the switch.
Micrel, Inc.
May 2007
P
L
=
DCR
×
how
I
OUT
2
switching
L
) can be calculated by
losses
due
to
the
12
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
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.
S-D
Figure 6. Switching Transition Losses
) and the current through the switch (I
M9999-051707
MIC4720
S-D
) are