LM2936-33 National Semiconductor, LM2936-33 Datasheet - Page 7

• Manufacturer Part Number: LM2936-33
• Description: Ultra-Low Quiescent Current 3.3V Regulator
• Manufacturer: National Semiconductor

Applications Information
Under conditions of higher ambient temperatures, the volt-
age and current calculated in the previous examples will
drop. For instance, at the maximum ambient of 125˚C the
LM2936Z-3.3 can only dissipate 128 mW, limiting the input
voltage to 5.6V for a 50 mA load, or 3.0 mA output current for
a 40V input.
The junction to ambient thermal resistance θ
two distinct components: the junction to case thermal resis-
tance rating θ
rating θ
For the SO-8 and TO-252 surface mount packages the θ
rating can be improved by using the copper mounting pads
on the printed circuit board as a thermal conductive path to
extract heat from the package.
On the SO-8 package the four ground pins are thermally
connected to the backside of the die. Adding approximately
0.04 square inches of 2 oz. copper pad area to these four
pins will improve the θ
this extra pad are is placed directly beneath the package
there should not be any impact on board density.
On the TO-252 package the ground tab is thermally con-
nected to the backside of the die. Adding 1 square inch of 2
oz. copper pad area directly under the ground tab will im-
prove the θ
CA
. The relationship is defined as: θ
JA
JC
rating to approximately 50˚C/W.
; and the case to ambient thermal resistance
JA
rating to approximately 110˚C/W. If
JA
(Continued)
JA
= θ
rating has
JC
+ θ
CA
JA
.
7
While the LM2936 has an internally set thermal shutdown
point of typically 150˚C, this is intended as a safety feature
only. Continuous operation near the thermal shutdown tem-
perature should be avoided as it may have a negative affect
on the life of the device.
While the LM2936-3.3 will survive input transients to +60V,
output regulation is not guaranteed for input voltages greater
than 40V. The LM2936 will not withstand a output short
circuit with the input above 40V because of safe operating
area limitations in the internal PNP pass device. With input
voltages above 60V the LM2936 will break down with cata-
strophic effects on the regulator and possibly the load as
well. Do not use this device in a design where the input
operating voltage may exceed 40V, or where transients are
likely to exceed 60V.
Shutdown Pin
The LM2936BM has a pin for shutting down the regulator
output. Applying a Logic Level High (
pin will cause the output to turn off. Leaving the Shutdown
pin open, connecting it to Ground, or applying a Logic Level
Low (
<
0.6V) will allow the regulator output to turn on.
>
2.0V) to the Shutdown
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