Xilinx Boards and Kits

[gszakacs]

---

donwaltman wrote:

I don't see any other possibilities other than a broken 3002 except maybe a broken 11040 ADC.  However, Maxim like Xilinx is a reputable company and they don't put out trash, so I'm hestitant to rest on those conclusions.

---

 They probably weren't trash when they left Maxim.  It is possible that the 3002 was damaged by ESD

or momentary power supply overvoltage.

-- Gabor

[eteam00]

I'm currently using 8mA drive with slow slew.  There are three signals output from the FPGA- SCLK, CS and DOUT.  All are distorted (after the shifter), e.g. my 800khz serial clock never reaches zero and is nearly indistinquishable because of the skew.

After the MAX3002 shifter?  (it's important to be very specific in forum posts)

Did you verify the power supplies on the Maxim board?  All of them?

Next would be to probe the pins of the MAX3002 device.  After the supplies are verified.

-- Bob Elkind

[eteam00]

It is possible that the 3002 was damaged by ESD or momentary power supply overvoltage.

The MAX3002 is rated for 15KV ESD tolerance.  That's pretty good.

Here's another thought:  very carefully inspect the MAX3002 device, at position U5 on the Maxim board.  Make sure it is marked MAX3002, and not MAX3000 or MAX3000E.

-- Bob Elkind

[donwaltman]

I checked the supply for the VL side (2.5V) and for the VCC side (3.3V) and the enable (2.5V) directly from the pins on the chip.  The inputs and outputs were also read directly from the chip pins. 

There are no power supplies on the  Maxim board; it's all supplied from the Xilinx SP605.

Chip damage could have occurred, however I wouldn't think that all three in/outs would be damaged the same way and I have not powered the board externally, only from the SP605.

It almost seems like this bidirectional design may have its pecularities but I wouldn't think they would put it out there if it were that unreliable.

[donwaltman]

3002, did it

[eteam00]

3002, did it

Well, unless your scope inputs are set to 50-ohm input term instead of 1M-ohm, I have no brilliant ideas left.

If it was my board, I would fire up a soldering station and start lifting pins for further troubleshooting.  I wouldn't recommend that for anyone else.

-- Bob Elkind

[donwaltman]

Well thanks for all the help.  It at least gives me some confidence that I'm not crazy.  Tomorrow when I get access to the fine tip iron, I may lift the SCLK ADC pin. 

It's only an $80 eval board, but my greatest fear is getting another one and the same freaking thing happening. 

Thanks again for the help.  I'll post any significant findings.

[donwaltman]

     Just an update on the MAX3002 level changer where the input signals were steep-edged and square and the output was crap.  Bob Elkin had mentioned a scope probe, but the same probe had accurately measured the inputs and just to be sure I measured the resistance going into the scope through the probe and got about 10M.  After narrowly escaping state-mandated commitment, I tried another probe just for the hell of it.  The signal looked improved but still distorted.  I put the probe on 10:1 and got a perfect signal. 

    I'm guessing the original probe had a capacitive load, but I was still shocked that the load of a good probe on 1:1 was too much for this chip.  I guess the 6k output impedance was a clue. 

    I think the manufacturers should do a better job of specifically documenting this in their data sheets.

    Thanks to all who helped.

[eteam00 · Accepted solution]

To sum up, after 29 posts in this thread:

The appearance of a problem was due to either faulty scope probe or incorrect scope setting.

Agreed?  If this problem has been resolved, please mark the thread as 'solved'.

-- Bob Elkind