Datasheet

or
K
=
+
LOSSOUT
PP
OUT
P
K
=
IN
P
OUT
P
P
DISS-TOP
INTERNAL
SMALL
LARGE
PCB
DEVICE
P
DISS-PCB
P
DISS
T
JUNCTION
T
AMBIENT
C
T
J-PCB
C
T
J-CASE
R
T
J-PCB
R
T
J-CASE
C
T
CASE-AMB
T
CASE
EXTERNAL
P
DISS
T
PCB
R
T
PCB-AMB
C
T
PCB-AMB
R
T
CASE-AMB
LM2735
www.ti.com SNVS485F –JUNE 2007–REVISED APRIL 2013
Figure 29. Associated Thermal Model
Calculating Efficiency, and Junction Temperature
The complete LM2735 DC/DC converter efficiency (η) can be calculated in the following manner.
(18)
Power loss (P
LOSS
) is the sum of two types of losses in the converter, switching and conduction. Conduction
losses usually dominate at higher output loads, where as switching losses remain relatively fixed and dominate at
lower output loads.
Losses in the LM2735 Device: P
LOSS
= P
COND
+ P
SW
+ P
Q
Conversion ratio of the Boost Converter with conduction loss elements inserted:
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