OBSOLETE

LM2575EP, LM2575HVEP

SNVS301B – DECEMBER 2004 – REVISED APRIL 2013

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The peak inductor current, which is the same as the peak switch current, can be calculated from the following

formula:

where

•

(15)

Select an inductor that is rated for the peak current anticipated.

Also, the maximum voltage appearing across the regulator is the absolute sum of the input and output voltage.

For a

−12V output, the maximum input voltage for the LM2575EP is +28V, or +48V for the LM2575HVEP.

The Switchers Made Simple (version 3.3) design software can be used to determine the feasibility of regulator

designs using different topologies, different input-output parameters, different components, etc.

Figure 31. Inverting Buck-Boost Develops

−12V

NEGATIVE BOOST REGULATOR

Another variation on the buck-boost topology is the negative boost configuration. The circuit in Figure 32 accepts

an input voltage ranging from

−5V to −12V and provides a regulated −12V output. Input voltages greater than

−12V will cause the output to rise above −12V, but will not damage the regulator.

Because of the boosting function of this type of regulator, the switch current is relatively high, especially at low

input voltages. Output load current limitations are a result of the maximum current rating of the switch. Also,

boost regulators can not provide current limiting load protection in the event of a shorted load, so some other

means (such as a fuse) may be necessary.

Typical Load Current

Note: Pin numbers are for TO-220 package.

Figure 32. Negative Boost

22

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