Thin shots

Any help would be appreciated. I hit a lot of thin irons and I invariably top fairway woods. I've seen myself on video and I tend to raise up as I'm swing through the ball, losing my posture. I can't figure out why I'm doing this. My grip and set-up are good. I get in a good, coiled, on-plane position at the top. It's coming down that I lose it. Ball bound maybe?

practice your swing with your head placed on a spot on the wall.

Many people say "You lifted your head" when you top a ball, it is rarely the head that lifts, it's everything else.

I think you may be straightening your knees and spine as you transfer your weight to the left foot during the downswing, check this as you start to slide your hips to the left. Concentrate on maintaining your spine angle.