What is a trial court's obligation to instruct a defendant on a particular defense?

"In the absence of a request for a particular instruction, a trial court's obligation to instruct on a particular defense arises `"only if [1] it appears that the defendant is relying on such a defense, or [2] if there is substantial evidence supportive of such a defense and the defense is not inconsistent with the defendant's theory of the case."' [Citations.]" (People v. Dominguez (2006) 39 Cal.4th 1141, 1148, quoting People v. Barton (1995) 12 Cal.4th 186, 195, italics added.)