Author Topic: Faulty FPGA?  (Read 1798 times)

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Offline BoscoeTopic starter

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Faulty FPGA?
« on: April 23, 2017, 02:25:13 pm »
I'm having some strange issues with an FPGA on a custom board. I had copied and pasted he design and layout from a previous project that didn't have any issue so I'm confident the design is okay.

The issues I'm having are:

- A few GPIOs do not go to the VCCIO voltage (3.3V) instead they only reach around 1.4V and are very flaky with the pressure I apply with the probe making a difference.
- I'm try to use a PLL to create 80MHz from 100MHz which isn't working at all.

I assembled the PCB myself, the FPGA is an EP4CE6E22N, I've assembled a lot of PCBs in my time so confident it's okay. Could these issues be caused by ESD or a faulty IC?

Thanks
 

Offline radar_macgyver

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Re: Faulty FPGA?
« Reply #1 on: April 23, 2017, 02:46:58 pm »
- A few GPIOs do not go to the VCCIO voltage (3.3V) instead they only reach around 1.4V and are very flaky with the pressure I apply with the probe making a difference.

Sounds like a dry joint to me, possibly on a power pin.
 

Offline BoscoeTopic starter

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Re: Faulty FPGA?
« Reply #2 on: April 23, 2017, 03:29:37 pm »
I forgot to mention if I assign the pin a value such as 'ft_nrst = 1' in the signal list in the top module without any other driver I get the issue however only on a couple of pins. If I do not assign it in the signal list and do 'assign ft_nrst = 1' in the code section it does work. Anyone know why this might be the case?
 

Offline Daixiwen

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Re: Faulty FPGA?
« Reply #3 on: April 24, 2017, 07:28:39 am »
Is the exposed pad properly connected to ground? A common problem on the E144 package is a bad connection on the exposed pad, giving all kind of weird problems.
 

Offline marshallh

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Re: Faulty FPGA?
« Reply #4 on: April 25, 2017, 02:26:02 am »
Is the exposed pad properly connected to ground? A common problem on the E144 package is a bad connection on the exposed pad, giving all kind of weird problems.

This, all sorts of weird phenomena occur if the center pad is not WELL soldered. If you want to hand solder it you bascally have to make a board cutout and manually solder it from underneath. Never had a problem reflowing them.
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