lm2594hvmx-adj National Semiconductor Corporation, lm2594hvmx-adj Datasheet - Page 25

• Manufacturer Part Number: lm2594hvmx-adj
• Description: Simple Switcher Power Converter 150 Khz 0.5a Step-down Voltage Regulator
• Manufacturer: National Semiconductor Corporation

Application Information
put reaches its nominal output voltage. The actual time de-
pends 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 rela-
tively high startup currents required by the inverting topology,
the delayed startup feature (C1, R
25 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 in-
put current needed for startup is now supplied by the input
capacitor (C
pacitor can be made much larger than normal.
IN
). For severe start up conditions, the input ca-
FIGURE 28. Inverting Regulator Ground Referenced Shutdown using Opto Device
FIGURE 27. Inverting Regulator Ground Referenced Shutdown
1
and R
(Continued)
2
) shown in Figure
25
INVERTING REGULATOR SHUTDOWN METHODS
To use the ON /OFF pin in a standard buck configuration is
simple, pull it below 1.3V (
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 27 and Figure 28 .
DS012439-42
@
25˚C, referenced to ground) to
DS012439-43
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