lm2936qmx-5.0 National Semiconductor Corporation, lm2936qmx-5.0 Datasheet - Page 8

• Manufacturer Part Number: lm2936qmx-5.0
• Description: Lm2936q Ultra-low Quiescent Current Ldo Voltage Regulator
• Manufacturer: National Semiconductor Corporation

www.national.com
Applications Information
Unlike other PNP low dropout regulators, the LM2936Q re-
mains fully operational to 40V. Owing to power dissipation
characteristics of the available packages, full output current
cannot be guaranteed for all combinations of ambient tem-
perature and input voltage. As an example, consider an
LM2936QZ–5.0 operating at 25°C ambient. Using the formula
for maximum allowable power dissipation given in
we find that P
contribution of the quiescent current to total power dissipation
the maximum input voltage (while still delivering 50 mA output
current) is 17.3V. The LM2936QZ–5.0 will go into thermal
shutdown if it attempts to deliver full output current with an
input voltage of more than 17.3V. Similarly, at 40V input and
25°C ambient the LM2936QZ–5.0 can deliver 18 mA maxi-
mum.
Under conditions of higher ambient temperatures, the voltage
and current calculated in the previous examples will drop. For
instance, at the maximum ambient of 125°C the LM2936QZ–
5.0 can only dissipate 128 mW, limiting the input voltage to
7.34V for a 50 mA load, or 3.5 mA output current for a 40V
input.
The junction to ambient thermal resistance θ
distinct components: the junction to case thermal resistance
Dmax
= 641 mW at 25°C. Including the small
JA
rating has two
(Note
3) ,
8
rating θ
θ
For the SO-8 the θ
copper mounting pads on the printed circuit board as a ther-
mal conductive path to extract heat from the package.
On the SO-8 package the four ground pins are thermally con-
nected 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
pad are is placed directly beneath the package there should
not be any impact on board density.
While the LM2936Q has an internally set thermal shutdown
point of typically 160°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 LM2936Q maintains regulation to 60V, it will not
withstand a short circuit above 40V because of safe operating
area limitations in the internal PNP pass device. Above 60V
the LM2936Q will break down with catastrophic 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.
CA
. The relationship is defined as: θ
JC
; and the case to ambient thermal resistance rating
JA
rating to approximately 110°C/W. If this extra
JA
rating can be improved by using the
JA
= θ
JC
+ θ
CA
.