I’m sorry but you are mistaken, by key pinning I assume you mean HPKP?
If I meant this I would have written HPKP. Because HPKP is HTTP Public Key Pinning. Note the HTTP - that indicates that it’s a HTTP header (at least in this case).
So no what I meant is ‘normal’ key pinning: You grab the public key of your cert, put it into your app and allow only HTTPS connections which use this cert. As you control the app and it’s hardcoded public key it’s not possible to use another cert (at least if the implementation has no flaws, of course) and you can skip the CA-check for that cert as it’s neither necessary nor useful in this case.
But as I said this of course only works if you develop an app, which only connects to your own server.