LP2980 Datasheet, PDF (14/18 Pages) National Semiconductor (TI) – Micropower 50 mA Ultra Low-Dropout Regulator

Increasing Output Current
FIGURE 6. 5V/400mA Regulator
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The LP2980 can be used to control higher-current regulators,
by adding an external PNP pass device. With the PNP tran-
sistors shown in Figure 6, the output current can be as high
as 400 mA, as long as the input voltage is held within the Safe
Operation Boundary Curves shown below in Figure 7.
To ensure regulation, the minimum input voltage of this reg-
ulator is 6V. This “headroom” is the sum of the V_BE of the
external transistor and the dropout voltage of the LP2980.
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. Recommended devices (other PNP transistors can be
used if the current gain and voltage ratings are similar).
C. Capacitor is required for regulator stability. Minimum size
is shown, and may be increased without limit.
D. Increasing the output capacitance improves transient re-
sponse and increases phase margin.
E. Maximum safe input voltage and load current are limited
by power dissipation in the PNP pass transistor and the max-
imum ambient temperature for the specific application. If a
TO-92 transistor such as the MPS2907A is used, the thermal
resistance from junction-to-ambient is 180°C/W in still air.
Assuming a maximum allowable junction temperature of 150°
C for the MPS2907A device, the following curves show the
maximum V_IN and I_L values that may be safely used for sev-
eral ambient temperatures.
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FIGURE 7. Safe Operation Boundary Curves for
Figure 6
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