(2-way) bubble calling situation

[Gramps]

Here's an interesting bubble hand I just encountered. Big stack is pushing *any two* cards here.

$525+$30 Hold'em No Limit - Level VIII (200/400) - 2006/10/25 - 20:29:44 (ET)

UTG (700 in chips)
Button (10175 in chips)
SB (1655 in chips)
BB (970 in chips)

SB posts the ante 25
UTG posts the ante 25**
Button posts the ante 25
BB posts the ante 25

UTG folds
Big STack raises 9400 to 9800
SB folds
BB looks down and sees ____ and calls off his last 545 chips

What's the least BB has to have here to make his call correct if you give big stack a true range of 100%? What if the big stack (whether correct or not) folds his worst ~1/2 hands and only is pushing top 50% here (you've seen evidence from recent/past play that where the BB gets < 3 BB or so in these bubble spots, the big stack will back off a fair amount, etc.).