Datasheet
T
JA
<
T
J-MAX
± T
A-MAX
P
IC_LOSS
T
JA
<
(125 - 50) °C
5.3 W
< 14.15
°C
W
500
T
CA
Board Area_cm
2
8
°C x cm
2
W
.
T
CA
<
125°C ± 50°C
5.3 W
- 1.0
°C
W
< 13.15
°C
W
T
CA
<
T
J-MAX
± T
A-MAX
P
IC_LOSS
- T
JC
LMZ13610
www.ti.com
SNVS709E –MARCH 2011–REVISED OCTOBER 2013
POWER DISSIPATION AND BOARD THERMAL REQUIREMENTS
When calculating module dissipation use the maximum input voltage and the average output current for the
application. Many common operating conditions are provided in the characteristic curves such that less common
applications can be derived through interpolation. In all designs, the junction temperature must be kept below the
rated maximum of 125°C.
For the design case of V
IN
= 12V, V
OUT
= 3.3V, I
OUT
= 10A, and T
A-MAX
= 50°C, the module must see a thermal
resistance from case to ambient (θ
CA
) of less than:
(13)
Given the typical thermal resistance from junction to case (θ
JC
) to be 1.0 °C/W. Use the 85°C power dissipation
curves in the Typical Performance Characteristics section to estimate the P
IC-LOSS
for the application being
designed. In this application it is 5.3W.
(14)
To reach θ
CA
= 13.15, the PCB is required to dissipate heat effectively. With no airflow and no external heat-sink,
a good estimate of the required board area covered by 2 oz. copper on both the top and bottom metal layers is:
(15)
As a result, approximately 38.02 square cm of 2 oz copper on top and bottom layers is the minimum required
area for the example PCB design. This is 6.16 x 6.16 cm (2.42 x 2.42 in) square. The PCB copper heat sink
must be connected to the exposed pad. For best performance, use approximately 100, 8mil thermal vias spaced
59 mil (1.5 mm) apart connect the top copper to the bottom copper.
Another way to estimate the temperature rise of a design is using θ
JA
. An estimate of θ
JA
for varying heat sinking
copper areas and airflows can be found in the Typical Performance Characteristics. If our design required the
same operating conditions as before but had 225 LFPM of airflow. We locate the required θ
JA
of
(16)
On the Theta JA vs copper heatsinking curve, the copper area required for this application is now only 2 square
inches. The airflow reduced the required heat sinking area by a factor of three.
To reduce the heat sinking copper area further, this package is compatible with D3-PAK surface mount heat
sinks.
For an example of a high thermal performance PCB layout for SIMPLE SWITCHER power modules, refer to AN-
2093 (SNVA460), AN-2084 (SNVA456), AN-2125 (SNVA473), AN-2020 (SNVA419) and AN-2026 (SNVA424).
Copyright © 2011–2013, Texas Instruments Incorporated Submit Documentation Feedback 19
Product Folder Links: LMZ13610