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Does your board allow to detect easily if it's actually a VCCPT short or a PCB respectively solder short? Also a broken bypass MLCC or tantal cap should be considered.
If the short is actually inside the FPGA, a serious violation of maximum ratings for VCCPT would be the most likely explanation.
By the way, could you clearly detect a short? Core voltage supplies may have low resistance in unpowered state and also show considerable start-up currents in some cases. I'm not sure for Stratix IV, please check the handbook thorougly. It may be also a case of insufficient power delivery of your VCCPT supply.
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thanks for reply
we take the FPGA off of the PCB board yesterday ,and test the FPGA,and found it is only 1ohm between VCCPT and GND.
i know some power pin have low resistance with GND ,just like Core voltage which is only 2ohm. But VCCPT is not like that if it is ok.
Maybe something wrong with the power supply (PTH05010w),but it's ok when we test it .VCCIO (bank 7\8) of this FPGA also connect to the same power supply,but it's ok.And the resistance between VCCIO and GND is normol.
So i want to know if there is something wrong about the FPGA itself,before the first configuration.
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