Datasheet

R
T
JA
=
165
o
C - 94
o
C
322 mW
= 220
o
C/W
6P
COND
+ P
SWF
+ P
SWR
+ P
Q
+ P
BOOST
= P
INTERNAL
P
INTERNAL
= 322 mW
R
T
JA
=
165
o
C - T
A
P
INTERNAL
LM2734Z
SNVS334E –JANUARY 2005–REVISED APRIL 2013 www.ti.com
(44)
Once this is determined, the maximum ambient temperature allowed for a desired junction temperature can be
found.
Design Example 3:
Operating Conditions
Package SOT-6
V
IN
12.0V P
OUT
2.475W
V
OUT
3.30V P
DIODE
523mW
I
OUT
750mA P
IND
56.25mW
V
D
0.35V P
SWF
108mW
Freq 3MHz P
SWR
108mW
I
Q
1.5mA P
COND
68.2mW
I
BOOST
4mA P
Q
18mW
V
BOOST
5V P
BOOST
20mW
T
RISE
8ns P
LOSS
902mW
T
FALL
8ns
R
DSON
400mΩ
IND
DCR
75mΩ
D 30.3%
(45)
Using a standard Texas Instruments Thin SOT-6 demonstration board to determine the R
θJA
of the board. The
four layer PCB is constructed using FR4 with 1/2oz copper traces. The copper ground plane is on the bottom
layer. The ground plane is accessed by two vias. The board measures 2.5cm x 3cm. It was placed in an oven
with no forced airflow.
The ambient temperature was raised to 94°C, and at that temperature, the device went into thermal shutdown.
(46)
If the junction temperature was to be kept below 125°C, then the ambient temperature cannot go above 54.2°C.
T
J
- (R
θJA
x P
LOSS
) = T
A
(47)
The method described above to find the junction temperature in the Thin SOT-6 package can also be used to
calculate the junction temperature in the WSON package. The 6 pin WSON package has a R
θJC
= 20°C/W, and
R
θJA
can vary depending on the application. R
θJA
can be calculated in the same manner as described in method
#2 (see example 3).
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