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I think what you are trying to say is you can use a buck CONTROLLER in an inverting buck boost, but then you drew an upsidedown (inverted) boost as referenced in the maxim document. How you arrange and connect the components matters. You didn't connect the load to v-out and ground, you connected it to v-in and v-out(and now the capacitor is out of place). I thought you were talking about a buck converter, then an inverting buck/boost converter, when really a low-side boost converter is what you meant (with the inductor and diode on the bottom and the diode reversed). Instead of boosting the top rail, it boosts the bottom rail more negative.
note: either boost or inverted boost can buck in the other direction if you use a half bridge. There is no forward buck, different control scheme. review (b) in the previous picture.
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