LP2980-N_16 Datasheet, PDF (18/30 Pages) Texas Instruments – Micropower 50-mA Ultra Low-Dropout Regulator in SOT-23 Package

LP2980-N
SNOS733O – APRIL 2000 – REVISED JUNE 2015
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Figure 37. Safe Operation Boundary Curves for Figure 36
With limited input voltage range, the LP2980-N can control a 3.3-V, 3-A regulator with the use of a high current-
gain external PNP pass transistor as shown in Figure 38. If the regulator is to be loaded with the full 3 A, heat
sinking will be required on the pass transistor to keep it within its rated temperature range. See Figure 39. For
best load regulation at the high load current, the LP2980-N output voltage connection should be made as close
to the load as possible.
Although this regulator can handle a much higher load current than can the LP2980-N alone, it can be shut down
in the same manner as the LP2980-N. When the ON/OFF control is brought low, the converter will be in
shutdown, and will draw less than 1 μA from the source.
Figure 38. 5 V to 3.3 V at 3-A Converter
NOTES:
Note A: Drive this input with a logic signal (see ON/OFF Input Operation). If the shutdown function is not to be
used, tie the ON/OFF pin directly to the IN pin.
Note B: Capacitor is required for regulator stability. Minimum size is shown, and may be increased without limit.
Note C: Increasing the output capacitance improves transient response and increases phase margin.
Note D: A heatsink may be required for this transistor. The maximum allowable value for thermal resistance of
the heatsink is dependent on ambient temperature and load current (see curves in Figure 39). 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.
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