LP38511_09 Datasheet, PDF (11/14 Pages) National Semiconductor (TI) – 800 mA Fast-Transient Response Low-Dropout Linear Voltage Regulator with Error Flag

FIGURE 2. ERROR Flag Operation, biased from V_IN
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POWER DISSIPATION/HEATSINKING
A heatsink may be required depending on the maximum pow-
er dissipation (P_D(MAX)), maximum ambient
temperature (T_A(MAX)) of the application, and the thermal re-
sistance (θ_JA) of the package. Under all possible conditions,
the junction temperature (T_J) must be within the range spec-
ified in the Operating Ratings. The total power dissipation of
the device is given by:
P_D = ( (V_IN−V_OUT) x I_OUT) + (V_IN x I_GND)
(1)
where I_GND is the operating ground current of the device
(specified under Electrical Characteristics).
The maximum allowable junction temperature rise (ΔT_J) de-
pends on the maximum expected ambient temperature (T_A
(MAX)^{) of the application, and the maximum allowable junction}
temperature (T_J(MAX)):
ΔT_J = T_J(MAX)− T_A(MAX)
(2)
The maximum allowable value for junction to ambient Ther-
mal Resistance, θ_JA, can be calculated using the formula:
θ_JA = ΔT_J / P_D(MAX)
(3)
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FIGURE 3. θ_JA vs Copper (1 Ounce) Area for TO-263
package
As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. The minimum
value for θ_JA for the TO-263 package mounted to a two-layer
PCB is 32°C/W.
Figure 4 shows the maximum allowable power dissipation for
TO-263 packages for different ambient temperatures, assum-
ing θ_JA is 35°C/W and the maximum junction temperature is
125°C.
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_JA of TO-263 package for
different copper area sizes, using a typical PCB with 1 ounce
copper and no solder mask over the copper area for heat
sinking.
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FIGURE 4. Maximum Power Dissipation vs Ambient
Temperature for TO-263 Package
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