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Unformatted text preview: ication, keeping other parameters the
same as above, now the dissipation would be 1.16
W, which exceeds the specification for IXD_409PI.
So in this case, it is recommended to use either the
IXD_409YI (TO -263 package) or IXD_409CI (TO220) package. Both these packages can dissipate
about 17 W with proper heat sinking arrangement.
The TO-263 is a surface mount package and can be
soldered onto a large pad on a copper surface of a
PCB for achieving good heat transfer. For TO -220
package, a heat sink can be used.
Let us take another example of a boost converter,
using IXFK55N50 at VDS = 250 VDC and at I =
D 27.5 Amps. Assuming sw = 500 kHz, Vcc = 12 V.
From the curve of Gate Charge for IXFK55N50 in
the Data Sheet one can determine that Qg = 370 nC.
Let us set R
Gext = 1.0 Ohm. We use IXD_414YI or
IXD_414CI here, which can dissipate 12W. Here
typical value of ROH = ROL = 0.6 Ohm. Substituting
the above values in our equation, we compute the
power dissipation to be:
PD = 0.6 x 12 x 370 x 500 kHz x 10-9
0.6 + 1.0 + 0.0
PD = 0.83 W.
With adequate air circulation, one may just be able
to use the PDIP Package. However, it is
recommended to use TO -263 or TO -220 package
for reliable performance.
For the third example, considering driving a large
size MOSFET module VMO 580-02F at fsw = 250
kHz. Let Vcc = 10 V, ROH = ROL = 0.6 Ohm, RGext=
0.0 Ohm. We read that Qg =2750 nC at Vcc = 10 V
off the VMO 580-02F data sheet. Now:
PD = 0.6 x 10 x 2750 x 250kHz x 10 -9
0.6+ 0.0 + 0.0
PD = 6.86 W IXAN0009 IXD_414YI (TO-263) or IXD_414CI (TO-220)
can easily drive this load provided adequate
heat sinking and proper airflow is maintained.
Comments above for mounting TO-263 and/or
TO-220 packages apply here as well. For
derating use 0.1 W/o C. So for an ambient
temperature of 50 o C, it works out to be 2.5 W.
As the limit of IXD_414YI or IXD_414CI is 12 W,
subtracting 2.5 W from this yields 9.5 W. So
6.86 W is still within limit. Thermal Impedance
(Junction to Case) is 0.55o C/W for TO -263 and
TO-220, hence a rise in case temperature
should be within limit. If we increase Vcc to 15V,
conduction losses in MOSFET could reduce due
to lower RDS(on), but obtaining the same rise...
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- Winter '08