Occasional ContributorCyclone IV GX Oscillator failures
We have an oscillator driving clock input through a 22 ohm resistor. The trace is very very short.
We produced 30 boards and had 6 oscillators fail.
We have done many PCIe designs with the CIVGX and have not seen this problem. All of the previous designs use a 50 MHz oscillator with a reconfig pll that generates 50 and 125 for the PCIe hard IP. We switched this one to 64 to improve the accuracy of an 8MHz clock output and forgot to change the reconfig pll inclk settings. The PCIe actually worked until a board failed. then we fixed all of the plls that we had programmed.
Replacing the oscillator fixes the board temporarily. The oscillators fail again several hours to a day later. We have tried several different types and manufacturers of the oscillators.
I replaced the 22 ohm resistor with a 220 in an attempt to characterize the output and input. The FPGA operates normally and doesn't seem to present much of a load. I can see the effect of a scope probe on the input, and the FPGA input is not much more.
Both oscillators with the 220 ohm resistors have eventually failed.
The oscillator and the FPGA are powered from the same 3.3V supply coming from a PCIe slot in a computer and are located directly next to the gold fingers.
I don't see any power supply noise, and 3 different test environments have been used.
I don't see any kind of output characterizations or detailed data for the oscillator.
Any help here would be greatly appreciated.
1) 50 MHz oscillator with 50 MHz design in the FPGA was tested w/ no failures. 10 of these units are being used in the field.
2) During qualification testing, it's discovered that an 8 MHz output is actually 8.006 MHz. The internal divider is set to 32/25 and the output should be exact. I couldn't fix this in the FPGA.
3) I change the 50 MHz oscillator to 64 MHz and the PLL to 1/1 and now my 8 MHz is really 8 +/- 50 ppm.
4) All of the boards that I have are re-tested and a few are sent to be used.
5) One of the boards that I have and one in the field show no activity on the PCIe. Then 2 more.
6) The PLL that drives the PCIe still has an INCLK value of 50 MHz. The downstream values of the PLL should be 50, 125, 312.50, and 1250 but are actually running at 64, 160, 400, and 1600. I fixed the INCLK value of that PLL, but the boards do not recover.
7) The failed boards have little or no amplitude on the 64 MHz, so we replace those oscillators. The oscillators all fail within 24 hours.
We bought several different kinds of oscillators -- same results. -- The oscillators all fail within 24 hours. 9) I replaced the 22 ohm series termination with 220 -- same results. -- The oscillators all fail within 24 hours.
10) I contacted EPSON and Abracon engineers who told me that the oscillators will tolerate a short circuit indefinitely and recover when the short is removed.
11) I replaced 2 FPGAs so far and they have been in continuous operation for 3 days now. I'm sending 2 more out to be replaced.
12) I have 11 boards that have never failed in a burn-in environment and have been running for 3 days.
So, YES the FPGAs were damaged and somehow killed bulletproof oscillators along the way.
In the timing analyzer, the higher clock values are shown to be derived. Other than that, there was no way to tell that my chips were time bombs in the field.
