. as you mentioned '는데' has some background information,(usually nagative meaning) A: will you go to shoping now?(지금 쇼핑하러 갈까?) B: i'm too sleepy now so.....(나 지금 많이 졸리는데..) 'i don't wanna go' is omitted (가기 싫은데, 안가면 안될까? 라는 의미를 함축하고 있음) one more example A: will you give me a cigarette?( 담배 한개 줄래?) B: I quit smoking since last week..(나 지난주부터 담배 끊었는데....) "i don't have one" is omitted (나 담배 없어) in those case, you can use "나 많이 졸려요" "나 지난주 부터 담배 끊었어" but it's a kind of habit that korean usally don't like to speak direct way.. but want others understand them... it's a culture difference... but as you know, it's depends on person. not all korean. ^^. and one more thing ~ 는데, used in other situation.. 밥 먹는데 얼마나 걸리니?(how long does it take to eat your meal?) 할수 있는데 까지 해보지 뭐?(I'll do what i can do) making verb to noun ^^ you can use it!

It's a versatile word that means "and", "but", "by the way". 나 뭐 좀 물어볼 게 있어. I have something to ask. 나 뭐 좀 물어볼 게 있는데. I have something to ask. (implies "Do you mind my asking?") 뭐해? What are you doing? 뭐하는데? What are you doing? 뭐하는데 implies: - I have something to do with you. - I'd like you to do something. " - (or just simply) I'm curious. If someone does something instead of what they're supposed to do, you can say "뭐하는데?! What are you doing?! (That's not what you're told to do!)" 나 졸린데 커피 좀 사다줄 수 있어? I'm sleepy, could you please buy me a cup of coffee? This one is what you're told about. And about the last two examples Hoon mentions, those are the different word, -는 데.