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
DRB
KTT
P
D
+
ǒ
V
IN
* V
OUT
Ǔ
I
OUT
TPS796
www.ti.com SLVS351O –SEPTEMBER 2002 –REVISED NOVEMBER 2013
THERMAL INFORMATION
Knowing the maximum R
θJA
, the minimum amount of
POWER DISSIPATION
PCB copper area needed for appropriate heatsinking
can be estimated using Figure 24.
Knowing the device power dissipation and proper
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 4:
(4)
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 the SON (DRB) package, the primary conduction
path for heat is through the exposed pad to the
printed circuit board (PCB). The pad can be
Note: θ
JA
value at board size of 9in
2
(that is, 3in ×
connected to ground or be left floating; however, it
3in) is a JEDEC standard.
should be attached to an appropriate amount of
copper PCB area to ensure the device does not
Figure 24. θ
JA
vs Board Size
overheat. On both SOT-223 (DCQ) and DDPAK
(KTT) packages, the primary conduction path for heat
Figure 24 shows the variation of θ
JA
as a function of
is through the tab to the PCB. That tab should be
ground plane copper area in the board. It is intended
connected to ground. The maximum junction-to-
only as a guideline to demonstrate the effects of heat
ambient thermal resistance depends on the maximum
spreading in the ground plane and should not be
ambient temperature, maximum device junction
used to estimate actual thermal performance in real
temperature, and power dissipation of the device and
application environments.
can be calculated using Equation 5:
NOTE: When the device is mounted on an
application PCB, it is strongly recommended to use
(5)
Ψ
JT
and Ψ
JB
, as explained in the Estimating Junction
Temperature section.
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