IL2575-xx
Figure 16. Inverting Buck–Boost
Regulator with Delayed Startup
It has been already mentioned above, that in some situations, the delayed startup or the undervoltage
lockout features could be very useful. A delayed startup circuit applied to a buck–boost converter is shown in
Figure 16.
Figure 22 in the “Undervoltage Lockout” section describes an undervoltage lockout feature for the same
converter topology.
NOTE: This picture does not show the complete circuit.
Figure 17. Inverting Buck–Boost Regulator Shut Down
Circuit Using an Optocoupler
With the inverting configuration, the use of the ON/OFF pin requires some level shifting techniques.
This is caused by the fact, that the ground pin of the converter IC is no longer at ground. Now, the ON/OFF
pin threshold voltage (1.4 V approximately) has to be related to the negative output voltage level. There are
many different possible shut down methods, two of them are shown in Figures 17 and 18.
Rev. 00
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