SLUS593B 鈭?DECEMBER 2003 鈭?REVISED APRIL 2004
TPS40054
TPS40055
TPS40057
APPLICATION INFORMATION
The switching losses for the high-side MOSFET are descibed in equation (33).
P
SW(fsw)
+
V
IN
where:
I
OUT
t
SW
f
SW
(Watts)
(33)
D
I
O
is the DC output current
D
t
SW
is the switching rise time, typically < 20 ns
D
f
SW
is the switching frequency
Typical switching waveforms are shown in Figure 13.
ID2
IO
ID1
d
BODY DIODE
CONDUCTION
1鈭抎
BODY DIODE
CONDUCTION
}
鈭咺
SW
0
ANTI鈭扖ROSS
CONDUCTION
SYNCHRONOUS
RECTIFIER ON
HIGH SIDE ON
UDG鈭?2139
Figure 14. Inductor Current and SW Node Waveforms
The maximum allowable power dissipation in the MOSFET is determined by equation (34).
P
T
+
where:
P
T
+
P
COND
)
P
SW(fsw)
(Watts)
and
胃
JA
is the package thermal impedance.
(35)
T
J
*
T
A
q
JA
(Watts)
(34)
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