I had this problem with a 12 wk old rescue aussie, he was fine the first few days and then decided to go to town on my cats
I do not like to get 'physical' either, but this puppy meant business, he'd pounce, pin, (the cats would play dead), and ra ra ra in right in their faces like he was daring them to move
First time he did it, I grabbed him by the back of the scruff, and yanked him off, telling him to "leave it" and I got in HIS face, 2nd time, I got a little more intense, same correction, but grabbed him by the scruff, and really got in his face with the wraith of mom...I think he might have done it again, can't recall, but he hasn't done it since
He's now almost 13 years old..
I don't advocate what I DID to others, but sometimes extreme measures call for extreme action
While your dog may just want to play, he could unintentionally really hurt the cat..
Have you tried using a squirt bottle on him,,or try redirecting the puppy if he even "thinks" about jumping the cat??