(Reuters) – Hewlett-Packard Co said its interim Chairman Ralph Whitworth resigned from the board of directors, effective July 16, to focus on his health. Whitworth, who runs activist hedge fund Relational Investors LLC, joined HPs board in 2011. He was appointed HPs interim chairman last year. HPs shares were down slightly at $34.01 in premarket trading on Tuesday. (Reporting by Supantha Mukherjee in Bangalore; Editing by Kirti Pandey)