Datasheet

LP2980-N
www.ti.com SNOS733M –APRIL 2000–REVISED JUNE 2013
Increasing Output Current
Figure 39. 5V/400mA Regulator
The LP2980-N can be used to control higher-current regulators, by adding an external PNP pass device. With
the PNP transistors shown in Figure 39, 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 40.
To ensure regulation, the minimum input voltage of this regulator is 6V. This “headroom” is the sum of the V
BE
of
the external transistor and the dropout voltage of the LP2980-N.
Notes:
1. 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.
2. Recommended devices (other PNP transistors can be used if the current gain and voltage ratings are
similar).
3. Capacitor is required for regulator stability. Minimum size is shown, and may be increased without limit.
4. Increasing the output capacitance improves transient response and increases phase margin.
5. Maximum safe input voltage and load current are limited by power dissipation in the PNP pass transistor and
the maximum 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 several ambient temperatures.
Figure 40. Safe Operation Boundary Curves for Figure 39
Copyright © 2000–2013, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Links: LP2980-N