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BrianSune_Froum's avatar
BrianSune_Froum
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5 months ago
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Cyclone V custom board VCCIO puzzling behavior

Dear Intel and all, I am working on Cyclone V soc 5CSEBA5U19C8N. There is a very puzzling VCCIO behavior. According to "Cyclone® V Device Family Pin Connection Guidelines PCG-01014-3.2". Any 3...
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  • BrianSune_Froum's avatar
    BrianSune_Froum
    5 months ago

    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?

FvM's avatar
FvM
Icon for Super Contributor rankSuper Contributor
5 months ago
Hi,
result 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?
BrianSune_Froum's avatar
BrianSune_Froum
Icon for Contributor rankContributor
5 months ago

No 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.