Datasheet

LM2592HV
www.ti.com SNVS075C –MAY 2001–REVISED APRIL 2013
C
IN
— 68 μF/25V Tant. Sprague 595D
470 μF/50V Elec. Panasonic HFQ
C
OUT
— 47 μF/20V Tant. Sprague 595D
220 μF/25V Elec. Panasonic HFQ
Figure 33. Inverting −5V Regulator with Delayed Startup
Because of differences in the operation of the inverting regulator, the standard design procedure is not used to
select the inductor value. In the majority of designs, a 33 μH, 4A inductor is the best choice. Capacitor selection
can also be narrowed down to just a few values.
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 LM2592HV current limit (approx 4A) 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 33 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.
lNVERTING 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 34
and Figure 35.
Figure 34. Inverting Regulator Ground Referenced Shutdown
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