Datasheet


SLVS612 − APRIL 2006
17
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APPLICATION INFORMATION
UDG−0213
9
∆
I
ANTI−CROSS
CONDUCTION
SYNCHRONOUS
RECTIFIER ON
BODY DIODE
CONDUCTION
BODY DIODE
CONDUCTION
HIGH SIDE ON
I
D1
I
D2
I
O
SW
0
}
d 1−d
Figure 9. Inductor Current and SW Node Waveforms
The maximum allowable power dissipation in the MOSFET is determined by equation (29).
P
T
+
ǒ
T
J
* T
A
Ǔ
q
JA
(Watts)
where:
P
T
+ P
COND
) P
SW(fsw)
(Watts)
and θ
JA
is the package thermal impedance.
Synchronous Rectifier MOSFET Power Dissipation
The power dissipated in the synchronous rectifier MOSFET is comprised of three components: R
DS(on)
conduction losses, body diode conduction losses, and reverse recovery losses. R
DS(on
) conduction losses can
be found using equation (32) and the RMS current through the synchronous rectifier MOSFET is described in
equation (31).
I
RMS
+ I
O
1 * d
Ǹ
ǒ
Amperes
RMS
Ǔ
The body-diode conduction losses are due to forward conduction of the body diode during the anti−cross
conduction delay time. The body diode conduction losses are described by equation (32).
P
DC
+ 2 I
O
V
F
t
DELAY
f
SW
(Watts)
where:
D V
F
is the body diode forward voltage
D t
DELAY
is the total delay time just before the SW node rises.
(29)
(30)
(31)
(32)