IL2596-xx

Because of differences in the operation of the inverting regulator, the standard design procedure is not used to select the

inductor value. In the majority of designs, a 33 µH, 3.5A inductor is the best choice. Capacitor selection can also be narrowed

down to just a few values. Using the values shown in Figure 7will provide good results in the majority of inverting designs.

This type of inverting regulator can require relatively large amounts of input current when starting up, even with light

loads. Input currents as high as the IL2596 current limit (approx 4.5A) are needed for at least 2 ms or more, until the output

reaches its nominal output voltage. The actual time depends 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

higher voltage before the switcher begins operating. A portion of the high input current needed for startup is now supplied by the

INVERTING REGULATOR SHUTDOWN METHODS

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 9and 10.

Figure 9. Inverting Regulator Ground Referenced Shutdown

Figure 10. Inverting Regulator Ground Referenced Shutdown using Opto Device

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Rev. 03