The Federal Trade Commission has requested additional information and documentary materials from Amazon.com Inc.          AMZN,         -1.52%        and Roomba parent iRobot Corp.          IRBT,         -0.43%        relating to their planned merger, according to a regulatory filing on Tuesday. The companies expect to promptly respond to the request, which will extend the waiting period imposed by the  Hart-Scott-Rodino Antitrust Improvements Act until 30 days after they have complied. Amazon announced plans to acquire iRobot for $61 a share in cash in August, in a deal that values the company at about $1.7 billion, including debt. iRobot shares were down 1.4% premarket and have fallen 12% in the year to date, while the S&P 500          SPX,         -1.20%        has fallen 18%.