IRF7335D1 International Rectifier, IRF7335D1 Datasheet - Page 10

• Manufacturer Part Number: IRF7335D1
• Description: Dual FETKY CO-PACKAGED DUAL MOSFET PLUS SCHOTTKY DIODE
• Manufacturer: International Rectifier

Control FET
P
P
Power MOSFET Selection for Non-Isolated DC/DC Converters
10
loss
loss
This can be expanded and approximated by;
= P
I
Q
I
Q
rms
conduction
g
2
oss
2
Q
i
V
g
gd
g
R
V
ds(on )
in
+ P
V
f
in
f
switching
f
+ P
I
drive
Q
+ P
i
gs 2
g
output
V
in
f
Synchronous FET
by;
*dissipated primarily in Q1.
portant characteristic; however, once again the im-
portance of gate charge must not be overlooked since
it impacts three critical areas. Under light load the
MOSFET must still be turned on and off by the con-
trol IC so the gate drive losses become much more
significant. Secondly, the output charge Q
verse recovery charge Q
are transfered to Q1 and increase the dissipation in
that device. Thirdly, gate charge will impact the
MOSFETs’ susceptibility to Cdv/dt turn on.
of the converter and therefore sees transitions be-
tween ground and V
a rate of change of drain voltage dV/dt which is ca-
pacitively coupled to the gate of Q2 and can induce
a voltage spike on the gate that is sufficient to turn
the MOSFET on, resulting in shoot-through current .
The ratio of Q
potential for Cdv/dt turn on.
Figure A: Q
P
P
loss
loss
The power loss equation for Q2 is approximated
For the synchronous MOSFET Q2, R
The drain of Q2 is connected to the switching node
P
I
conduction
Q
rms
Q
oss
g
2
oss
2
Characteristic
gd
/Q
V
R
g
gs1
V
ds(on)
in
in
must be minimized to reduce the
P
. As Q1 turns on and off there is
drive
f
f
rr
both generate losses that
P
output
*
Q
rr
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V
in
ds(on)
oss
is an im-
f
and re-