LP2980 Datasheet, PDF (15/18 Pages) National Semiconductor (TI) – Micropower 50 mA Ultra Low-Dropout Regulator

Typical Applications (Continued)
brought low, the converter will be in shutdown, and will draw
less than 1 µA from the source.
Notes:
A. Drive this input with a logic signal (see Application Hints).
If the shutdown function is not to be used, tie the ON/OFF
pin directly to the V_IN pin.
B. Capacitor is required for regulator stability. Minimum size
is shown, and may be increased without limit.
C. Increasing the output capacitance improves transient re-
sponse and increases phase margin.
D. A heatsink may be required for this transistor. The maxi-
mum allowable value for thermal resistance of the heatsink
is dependent on ambient temperature and load current (see
curves in ). Once the value is obtained from the graph, a
heatsink must be selected which has a thermal resistance
equal to or lower than this value. If the value is above
60˚C/W, no heatsink is required (the TO-220 package alone
will safely dissipate this).
For these curves, a maximum junction temperature of 150˚C
is assumed for the pass transistor. The case-to-heatsink at-
tachment thermal resistance is assumed to be 1.5˚C/W. All
calculations are for 5.5V input voltage (which is worst-case
for power dissipation).
DS012078-54
FIGURE 8. Heatsink Thermal Resistance Requirements
for Figure 7
15
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