Datasheet

R
T
=
'T
Power
6P
COND
+ P
SW
+ P
DIODE
+ P
IND
+ P
Q
+ P
BOOST
= P
LOSS
LMR12010
www.ti.com SNVS731A –SEPTEMBER 2011–REVISED SEPTEMBER 2011
V
BOOST
is normally between 3VDC and 5VDC. The I
BOOST
rms current is approximately 4.25mA. Total power
losses are:
(37)
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 LMR12010 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 27. Cross-Sectional View of Integrated Circuit Mounted on a Printed Circuit Board.
Heat in the LMR12010 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:
(38)
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