Actel Silicon Explorer II User Manual page 31

VPP Pin
Internally, a diode exists between the VCC and VPP signal. Under
normal operating conditions (VPP tied high), this diode cannot be
forward-biased and the device draws normal operating current as
outlined in the Actel FPGA Data Book. If this diode becomes forward
biased (a potential risk if VPP floats and gets driven low), the device
draws excessive current. Also, we have found that the VPP pin is the
most sensitive pin to ESD on the RH1020 and RH1280.
Actel recommends that you connect the VPP pin be directly to the
VCC. Additionally, verify with an ohm meter that the VPP pins on all
flight devices are properly terminated.
Actel does not guarantee the long-term reliability of devices that were
not always in a legal operating configuration. No credible analysis has
been performed that would guarantee reliable operation of parts that
were not always in a legal operating configuration.
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