Datasheet

LM2595
SNVS122B –MAY 1999–REVISED APRIL 2013 www.ti.com
This type of inverting regulator can require relatively large amounts of input current when starting up, even with
light loads. Input currents as high as the LM2595 current limit (approx 1.5A) are needed for at least 2 ms or
more, until the output reaches its nominal output voltage. The actual time depends on the output voltage and the
size of the output capacitor. Input power sources that are current limited or sources that can not deliver these
currents without getting loaded down, may not work correctly. Because of the relatively high startup currents
required by the inverting topology, the delayed startup feature (C1, R
1
and R
2
) shown in Figure 38 is
recommended. By delaying the regulator startup, the input capacitor is allowed to charge up to a higher voltage
before the switcher begins operating. A portion of the high input current needed for startup is now supplied by the
input capacitor (C
IN
). For severe start up conditions, the input capacitor can be made much larger than normal.
INVERTING REGULATOR SHUTDOWN METHODS
To use the ON /OFF pin in a standard buck configuration is simple, pull it below 1.3V (@25°C, referenced to
ground) to turn regulator ON, pull it above 1.3V to shut the regulator OFF. With the inverting configuration, some
level shifting is required, because the ground pin of the regulator is no longer at ground, but is now setting at the
negative output voltage level. Two different shutdown methods for inverting regulators are shown in Figure 40
and Figure 41.
Figure 40. Inverting Regulator Ground Referenced Shutdown
Figure 41. Inverting Regulator Ground Referenced Shutdown using Opto Device
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