LM2597, LM2597HV
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SNVS119C –MARCH 1998–REVISED APRIL 2013
Figure 47. Typical Circuit Using Shutdown /Soft-start and Error Flag Features
Figure 48. Inverting −5V Regulator With Shutdown and Soft-start
lNVERTING REGULATOR
The circuit in Figure 48 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 regulates it.
This example uses the LM2597-5 to generate a −5V output, but other output voltages are possible by selecting
other output 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 maximum output current greatly
depends on both the input and output voltage. The curve shown in Figure 49 provides a guide as to the amount
of output load current possible for the different input and output voltage conditions.
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 converting +20V to −5V, the regulator would
see 25V between the input pin and ground pin. The LM2597 has a maximum input voltage rating of 40V (60V for
the LM2597HV).
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