The Philippines international has penned a one-month deal with Chris Powell's side, who moved for the stopper after injuries to Rob Elliot and Ross Worner.
Etheridge has yet to feature for the Cottagers' first team but progressed to No.2 behind David Stockdale during Mark Schwarzer's participation in the Asia Cup 2011.
The 21-year-old will stay at The Valley until April 5 and is eligible to feature in the Addicks' clash against MK Dons on Tuesday.
Source: PA
Source: PA