Datasheet

R
T
=
'T
Power
LM2734Z
SNVS334E –JANUARY 2005–REVISED APRIL 2013 www.ti.com
Design Example 1:
Operating Conditions
V
IN
5.0V P
OUT
2.5W
V
OUT
2.5V P
DIODE
151mW
I
OUT
1.0A P
IND
75mW
V
D
0.35V P
SWF
53mW
Freq 3MHz P
SWR
53mW
I
Q
1.5mA P
COND
187mW
T
RISE
8ns P
Q
7.5mW
T
FALL
8ns P
BOOST
21mW
R
DSON
330mΩ P
LOSS
548mW
IND
DCR
75mΩ
D 0.568
η = 82%
Calculating the LM2734Z Junction Temperature
Thermal Definitions:
T
J
= Chip junction temperature
T
A
= Ambient temperature
R
θJC
= Thermal resistance from chip junction to device case
R
θJA
= Thermal resistance from chip junction to ambient air
Figure 13. Cross-Sectional View of Integrated Circuit Mounted on a Printed Circuit Board
Heat in the LM2734Z due to internal power dissipation is removed through conduction and/or convection.
Conduction: Heat transfer occurs through cross sectional areas of material. Depending on the material, the
transfer of heat can be considered to have poor to good thermal conductivity properties (insulator vs conductor).
Heat Transfer goes as:
silicon→package→lead frame→PCB.
Convection: Heat transfer is by means of airflow. This could be from a fan or natural convection. Natural
convection occurs when air currents rise from the hot device to cooler air.
Thermal impedance is defined as:
(39)
14 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated
Product Folder Links: LM2734Z