Preliminary
Thermal Considerations
EP1117
The EP1117 regulators have thermal protection to limit junction temperature to 150ºC. However, device
functionality is only guaranteed to a maximum junction temperature of +125ºC. A heat sink may be required
depending on the maximum power dissipation and maximum ambient temperature of the application. Figure 3
show for the SOT-223 the measured values
θ
(JA)
for different copper area sizes using a 2 layers, 1.6mm, and
6Sq. cm FR-4 PCB with 2oz. copper and a ground plane layer on the backside area used for heat sinking. It can
be used as a rough guideline in estimating thermal resistance. The SOT-223 packages use a copper plane on
the PCB and the PCB itself as a heat sink. To optimize the heat sinking ability of the plane and PCB, solder the
tab of the package to the plane.
Figure 3.
θ
(JA)
vs. copper area for SOT-223 package
The thermal resistance for each application will be affected by thermal interactions with other components on
the board. Some experimentation will be necessary to determine the actual value.
The power dissipation of EP1117 is equal to : PD = (V
IN
- V
OUT
) x I
OUT
Maximum junction temperature is equal to : T
JUNCTION
= T
AMBIENT
+ (P
D
x
θ
(JA)
)
Note: T
JUNCTION
must not exceed 125°C
Safe Operation Area
Using the experiment result of previous Thermal Consideration (choose the one with 1.5cm * 1.5cm polygene
area) and
θ
(JA)
= 50°C/W spec, the safe operation area of EP1117 in SOT-223 packages can be obtained as
Figure 4.
Figure 4. Safe Operation Area of EP1117 in SOT-223 packages
(Limited by Power Dissipation with T
JUNCTION
< 125°C)
Rev.01
7/8
ETC [ ETC ]
