The XPLA1 CPLD does not appear to start up on a low current (high impedance) supply. Are there any times that the CPLD requires a higher level of current?
There are two distinct times that XPLA1 devices require a higher amount of current to start.
During power-up, the CPLD monitors the level of VDD. At approximately 2.4V, the device recognizes that it has enough voltage to sustain operation, and it enters a configuration and reset mode. This requires about 50mA to 100mA for a short period of time (typically 20 microseconds or so). If this initial power is not available for startup, the device will not configure properly and will draw a higher amount of current for a sustained period of time. The part might also self-heat and resemble a "latched" part.
The CPLD also requires a larger amount of current (10mA to 100mA) during ISP operations. Program and Verify require a significant amount of current to correctly perform their operations.