当我爸爸还在睡觉时我离开了家 用英语说

I left home when my father was still sleeping.

i left home while my father was still in bed/sleeping.

i left home while（when） my father was still sleeping
这种是特定翻译“当…时候,怎么怎么养”,两个动作是同时发生的,一般用while连接,当然 用when也是可以的

i left home while my father was still sleeping..