"He smiled, walking towards the man." literally translates to: "Er lächelte, auf den Mann zugehend." This is the correct structure of the sentence you made: The participle is not split.
Please note that in German, the subject is with the main activity, and the participle denotes the side activity. I'm not sure whether this is the same for English.
The far more common form of this sentence is that "gehen" is the main activity, and "lächeln" will therefore be used in the participle form: "Lächelnd ging er auf den Mann zu."
While I am not an English major, I think "He walked towards the man, smiling." also is the more common form in English, and putting the verbs the other way around transports the same subtle change in meaning.