IL2575-XX Datasheet, PDF (10/17 Pages) IK Semicon Co., Ltd – 1.0 A, 15 V, Step-Down Switching Regulator

IL2575-xx
NOTE: This picture does not show the complete circuit.
Figure 18. Inverting Buck–Boost Regulator Shut Down
Circuit Using a PNP Transistor
Negative Boost Regulator
This example is a variation of the buck–boost topology and is called a negative boost regulator. This
regulator experiences relatively high switch current, especially at low input voltages. The internal switch
current limiting results in lower output load current capability.
The circuit in Figure 19 shows the negative boost configuration. The input voltage in this application
ranges from –5.0 V to –12 V and provides a regulated –12 V output.
If the input voltage is greater than –12 V, the output will rise above –12 V accordingly, but will not
damage the regulator.
Figure 19. Negative Boost Regulator
Design Recommendations:
The same design rules as for the previous inverting buck–boost converter can be applied. The output
capacitor Cout must be chosen larger than would be required for a standard buck converter. Low input
voltages or high output currents require a large value output capacitor (in the range of thousands of uF). The
recommended range of inductor values for the negative boost regulator is the same as for inverting
converter design.
Another important point is that these negative boost converters cannot provide current limiting load
protection in the event of a short in the output so some other means, such as a fuse, may be necessary to
provide the load protection.
Rev. 00