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ContributorCyclone V custom board VCCIO puzzling behavior
There are new measured data.
If I attached a simple 10k resistor to the 1.2V rail. it will drop back to normal 1.2 range.
But the loaded /w 10k is still measuring 40mV higher than unloaded DCDC w/o the FPGA chip.
So there are some leakage current inside the diode path? from VCCPD to VCCIO?
Super Contributorresult sounds promising, a lower pull-down value like 500R or 1k can hopefully cut unwanted VCCIO leakage. I'd however expect a statement from Intel support, it might be a known problem. Particularly we should get specification of maximal leakage current.
A final question, can you exclude that the problem is caused by a partly damaged device, e.g. due to ESD?
ContributorNo this theory don't holds. If it is damaged by ESD why only 1.2V is able to trigger a higher voltage?
I will highly expected :
A internal VCCPD diode is leakage due to VCCIO-VCCPD high at VCCIO low.
As V(diode) breakdown aka current increase when voltage increase aka basic diode IV model.
However if a ESD had break the barrier then no matter it is what voltage level.
I do measured via diode model on meter and all VCCPD and VCCIO related group is almost same.
The data last I got is that around 100uA to 1mA on VCCIO rail can easily remove the voltage increase behavior.
