More and more Xilinx families are becomimg available in 3.3 V versions, but not all Xilinx 3.3-V families are created equal. Here are the details:
XC2000L is the same die as XC2000, but the "L"-version is bonded differently, to make the chip wake up with CMOS thresholds ( 50% of Vcc, vs TTL thresholds in XC2000 ). The low-voltage detector is around 2.5 V for all XC2000 devices.
XC3000L is the same die as XC3000A, and XC3100L is the same die as XC3100A, but the "L" versions are specially bonded to make two changes: The device wakes up with CMOS input thresholds (50% of Vcc, vs TTL thresholds in XC3000A ), and the low-voltage detector kicks in at 2.5V (vs. 3.2V in the XC3000A ).
XC4000L is the same die as XC4000E, but the "L"-version is bonded differently, so that it wakes up with CMOS input thresholds. Both XC4000E and XC4000L have the low-voltage detector @ 2.5 V.
XC4000XL is a new design, circuit details are different from XC4000EX. Internal geometries are optimized for the 0.35 micron process and 3.3-V operation. The I/O structure is completely redesigned to achieve 5-V tolerance.
XC5200L is the same die as XC5200, but the "L" versions are specially bonded to make three changes: The low-voltage detector kicks in at 2.2V (vs. 3.2V in the XC5200 ), and the device wakes up with CMOS input thresholds =50% of Vcc Inputs are 5-V tolerant if one of the Vcc pin (called Vtt ) is connected to the 5-V Vcc. This is a simpler structure than the one in XC4000XL.
Note that XC3100L and XC5200L use a continuously running internal oscillator to generate an elevated voltage for driving the pass-transistor gates , This is called "pumped gates" and gives better speed, but results in significantly elevated idle ( quiescent ) current consumption, bad for battery-operated systems. XC3100 devices have always used this technique, while the original XC5200 devices did not, but the coming releases will.