LM317L MDA National Semiconductor, LM317L MDA Datasheet - Page 7

• Manufacturer Part Number: LM317L MDA
• Description: 3-Terminal Adjustable Regulator
• Manufacturer: National Semiconductor

Application Hints
mum. When the 1W pulse is ended, the thermal regulation
again shows a 7mV change as the gradients across the
LM317L chip die out. Note that the load regulation error of
about 14mV (0.14%) is additional to the thermal regulation
error.
PROTECTION DIODES
When external capacitors are used with any IC regulator it is
sometimes necessary to add protection diodes to prevent
the capacitors from discharging through low current points
into the regulator. Most 10µF capacitors have low enough
internal series resistance to deliver 20A spikes when
shorted. Although the surge is short, there is enough energy
to damage parts of the IC.
When an output capacitor is connected to a regulator and
the input is shorted, the output capacitor will discharge into
D1 protects against C1
D2 protects against C2
LM317L micro SMD Light Sensitivity
Exposing the LM317L micro SMD package to bright sunlight
may cause the V
of fluorescent lighting the output is not affected. The LM317
REF
to drop. In a normal office environment
(Continued)
FIGURE 3. Regulator with Protection Diodes
7
the output of the regulator. The discharge current depends
on the value of the capacitor, the output voltage of the
regulator, and the rate of decrease of V
this discharge path is through a large junction that is able to
sustain a 2A surge with no problem. This is not true of other
types of positive regulators. For output capacitors of 25 µF or
less, the LM317L’s ballast resistors and output structure limit
the peak current to a low enough level so that there is no
need to use a protection diode.
The bypass capacitor on the adjustment terminal can dis-
charge through a low current junction. Discharge occurs
when either the input or output is shorted. Internal to the
LM317L is a 50Ω resistor which limits the peak discharge
current. No protection is needed for output voltages of 25V
or less and 10µF capacitance. Figure 3 shows an LM317L
with protection diodes included for use with outputs greater
than 25V and high values of output capacitance.
micro SMD does not sustain permanent damage from light
exposure. Removing the light source will cause LM317L’s
V
REF
to recover to the proper value.
00906409
IN
. In the LM317L,
www.national.com