Financial terms of the deal weren't disclosed.
"I feel humbled and excited at the same time," McMichael said of joining the Chargers, according to the team's official Web site. "I feel like I've been in a dormant state for three years. I feel like my time has finally come. Sometimes you feel like you've got to wait for certain good things to happen to you, and this is a breath of fresh air. I'm excited to be here."
"We're excited to add Randy to the team," Turner said in a statement released by the team. "He brings experience and added depth to the tight end position."
The Associated Press contributed to this report.