LP38511-1.8 NSC [National Semiconductor], LP38511-1.8 Datasheet - Page 11

• Manufacturer Part Number: LP38511-1.8
• Description: 800 mA Fast-Transient Response Low-Dropout Linear Voltage Regulator with Error Flag
• Manufacturer: NSC [National Semiconductor]

POWER DISSIPATION/HEATSINKING
A heatsink may be required depending on the maximum pow-
er
temperature (T
sistance (θ
the junction temperature (T
ified in the Operating Ratings. The total power dissipation of
the device is given by:
where I
(specified under Electrical Characteristics).
The maximum allowable junction temperature rise (ΔT
pends on the maximum expected ambient temperature (T
(MAX)
temperature (T
The maximum allowable value for junction to ambient Ther-
mal Resistance, θ
HEATSINKING TO-263 PACKAGE
The TO-263 and the TO-263 THIN packages use the copper
plane on the PCB as a heatsink. The tab, or DAP, of these
packages are soldered to the copper plane for heat sinking.
Figure 3 shows a curve for the θ
different copper area sizes, using a typical PCB with 1 ounce
copper and no solder mask over the copper area for heat
sinking.
) of the application, and the maximum allowable junction
dissipation
P
GND
D
JA
= ( (V
is the operating ground current of the device
) of the package. Under all possible conditions,
J(MAX)
A(MAX)
ΔT
IN
θ
JA
−V
J
JA
, can be calculated using the formula:
):
= T
) of the application, and the thermal re-
OUT
= ΔT
(P
J(MAX)
) x I
D(MAX)
J
J
/ P
) must be within the range spec-
OUT
− T
D(MAX)
),
) + (V
A(MAX)
JA
of TO-263 package for
FIGURE 2. ERROR Flag Operation, biased from V
maximum
IN
x I
GND
)
ambient
J
) de-
(1)
(2)
(3)
A
11
As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. The minimum
value for θ
PCB is 32°C/W.
Figure 4 shows the maximum allowable power dissipation for
TO-263 packages for different ambient temperatures, assum-
ing θ
125°C.
FIGURE 3. θ
FIGURE 4. Maximum Power Dissipation vs Ambient
JA
is 35°C/W and the maximum junction temperature is
JA
Temperature for TO-263 Package
for the TO-263 package mounted to a two-layer
JA
vs Copper (1 Ounce) Area for TO-263
IN
package
20182935
20182934
20182936
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