Details weren't announced, but various reports said the extension was worth $11 million.
Smith's previous contract was due to expire following the 2009 season. He was promoted in April 2003 after John Butler died of cancer.
The Chargers have won the AFC West three times in four seasons under Smith. They'll try to break a four-game postseason losing streak dating to January 1995 when they host the Tennessee Titans on Sunday in the wild-card round.
GIANTS: The great unknown for New York in the playoffs is quarterback Eli Manning .
If Manning performs the way he did against the New England Patriots this past weekend, the Giants (10-6) have a good shot at beating the Buccaneers (9-7) in Tampa in Sunday's NFC wild-card game.
The concern is that the bad Manning could show up in the postseason once again. He is 0-for-2 in the playoffs.
In losing wild-card games to Carolina and Philadelphia the past two years, Manning was 26-of-45 for 274 yards, two touchdowns and four interceptions.
While the Giants had a heartbreaking 38-35 loss to the Patriots on Saturday, Manning was outstanding. He was 22-of-32 for 251 yards, with four touchdowns and one interception.
JAGUARS: Fred Taylor isn't worried as much about the Pittsburgh Steelers' home-field advantage as he is their bad field.
Taylor, one of Jacksonville's star running backs, chided the Steelers for their substandard grass field. He suggested they spend $1 million on artificial turf to improve one of the NFL's worst playing surfaces.
The Jaguars play an AFC wild-card game in Pittsburgh on Saturday night.
"That field is terrible," Taylor said in a conference call with Pittsburgh reporters. "That's a lawsuit pending. That's ridiculous."
Taylor's comments were unexpected only because he ran for 147 yards and the winning touchdown on that snow-covered, mushy field during Jacksonville's 29-22 victory in Pittsburgh on Dec. 16.
BRONCOS: Denver has more work to do in rebuilding its once-touted offensive line after left tackle Matt Lepsis told coach Mike Shanahan he's retiring.
Lepsis acknowledged his play slipped in his 11th season after returning from ACL surgery on his right knee.