LM2598S-ADJ National Semiconductor, LM2598S-ADJ Datasheet - Page 27

• Manufacturer Part Number: LM2598S-ADJ
• Description: SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator/ with Features
• Manufacturer: National Semiconductor

Application Information
lNVERTING REGULATOR
The circuit in Figure 26 converts a positive input voltage to a
negative output voltage with a common ground. The circuit
operates by bootstrapping the regulators ground pin to the
negative output voltage, then grounding the feedback pin,
the regulator senses the inverted output voltage and regu-
lates it.
This example uses the LM2598-5 to generate a −5V output,
but other output voltages are possible by selecting other out-
put voltage versions, including the adjustable version. Since
this regulator topology can produce an output voltage that is
either greater than or less than the input voltage, the maxi-
mum output current greatly depends on both the input and
output voltage. The curve shown in Figure 27 provides a
guide as to the amount of output load current possible for the
different input and output voltage conditions.
FIGURE 25. Typical Circuit Using Shutdown /Soft-start and Error Flag Features
FIGURE 26. Inverting −5V Regulator With Shutdown and Soft-start
(Continued)
27
The maximum voltage appearing across the regulator is the
absolute sum of the input and output voltage, and this must
be limited to a maximum of 40V. In this example, when con-
verting +20V to −5V, the regulator would see 25V between
the input pin and ground pin. The LM2598 has a maximum
input voltage rating of 40V.
DS012593-43
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DS012593-42