Datasheet

R
qJA
+
(
)125
O
C * T
A
)
P
D
160
140
120
100
80
60
40
20
0
q
JA
( C/W)
°
0 1 2 3
4 5
6
7
8 9 10
Board Copper Area ( )in
2
DCQ
DRV
DRB
P
D
+
ǒ
V
IN
* V
OUT
Ǔ
I
OUT
TPS737xx
www.ti.com SBVS067P –JANUARY 2006–REVISED JULY 2013
POWER DISSIPATION Knowing the maximum R
θJA
, the minimum amount of
PCB copper area needed for appropriate heatsinking
Knowing the device power dissipation and proper
can be estimated using Figure 33.
sizing of the thermal plane that is connected to the
tab or pad is critical to avoiding thermal shutdown
and ensuring reliable operation.
Power dissipation of the device depends on input
voltage and load conditions and can be calculated
using Equation 6:
(6)
Power dissipation can be minimized and greater
efficiency can be achieved by using the lowest
possible input voltage necessary to achieve the
required output voltage regulation.
On both SON (DRB) and SON (DRV) packages, the
primary conduction path for heat is through the
exposed pad to the printed circuit board (PCB). The
pad can be connected to ground or be left floating;
Note: θ
JA
value at board size of 9in
2
(that is, 3in ×
however, it should be attached to an appropriate
3in) is a JEDEC standard.
amount of copper PCB area to ensure the device
Figure 33. θ
JA
vs Board Size
does not overheat. On the SOT-223 (DCQ) package,
the primary conduction path for heat is through the
tab to the PCB. That tab should be connected to
Figure 33 shows the variation of θ
JA
as a function of
ground. The maximum junction-to-ambient thermal
ground plane copper area in the board. It is intended
resistance depends on the maximum ambient
only as a guideline to demonstrate the effects of heat
temperature, maximum device junction temperature,
spreading in the ground plane and should not be
and power dissipation of the device and can be
used to estimate actual thermal performance in real
calculated using Equation 7:
application environments.
NOTE: When the device is mounted on an
(7)
application PCB, it is strongly recommended to use
Ψ
JT
and Ψ
JB
, as explained in the Estimating Junction
Temperature section.
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