Datasheet

LM2991
SNVS099H –MAY 1999–REVISED JUNE 2013 www.ti.com
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Adjust Pin Current Low Voltage Behavior
Figure 15. Figure 16.
Maximum Power Maximum Power Dissipation
Dissipation (TO-220) (DDPAK/TO-263)
(1)
Figure 17. Figure 18.
(1) The maximum allowable power dissipation is a function of the maximum operating junction temperature (T
J(MAX))
, the thermal resistance
of the package (θ
JA
), and the ambient temperature (T
A
). The maximum allowable power dissipation is: P
D
= (T
J(MAX)
− T
A
)/θ
JA
, where
T
J(MAX)
is 125°C, and T
A
is the maximum expected ambient temperature. If this dissipation is exceeded, the die temperature will rise
above 125°C. Excessive power dissipation will cause the LM2991 to go into thermal shutdown (See Thermal Shutdown). For the
LM2991, the junction-to-ambient thermal resistance is 53°C/W for the TO-220, 73°C/W for the DDPAK/TO-263, and junction-to-case
thermal resistance is 3°C/W. If the DDPAK/TO-263 package is used, the thermal resistance can be reduced by increasing the PC board
copper area thermally connected to the package. Using 0.5 square inches of copper area, θ
JA
is 50°C/W; with 1 square inch of copper
area, θ
JA
is 37°C/W; and with 1.6 or more square inches of copper area, θ
JA
is 32°C/W.
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