DAC failure mode

Robert Latest · 2007-02-28T11:35:52+00:00

Hi folks,currently I'm looking at a piece of equipment (a PC32 DSP board from Innovative Integrations) that has an AD669 D/A converter on board. Instead of the desired sweep from -10V to +10V, I get an odd assortment of linear pieces that looks like this: output ^+10 | / / | / / | / /+5 |/ / | | |0---------------------> command (0-FFFF) / / / / / /-5 / /Or, in words: When the output should be -10V (input 0000), it is -5V and rises linearly. On the 3FFF->4000 transition, the output jumps back to -5V and then rises properly to 0. On 7FFF->8000, I get a jump to +5V and a ramp to +10V, at BFFF->C000 back to +5V, and another ramp to +10V which is reached at FFFF.Question: How can such an error arise? Is this a typical DAC failure mode? Is it possible to cause it through ESD at one (buffered) analog output? Stupid question of course. Anything can be caused by ESD. I wouldn't have expected a commercial product to be that susceptible though.The background is as follows: I've been asked by a colleague to look into a problem that he seemed to have with some circuit connected to the DAC output in question. To test that other thing (which turned out to be healthy) I connected it to the PC32's output, found weird behavior, and then found the problem on the PC32 itself. Now I'm being accused of having destroyed the PC32 by touching its outputs. I won't go into the details of the accompanying issues here, but up to this point I was the only one who didn't have severe problems with this socially weird fellow, who is now convinced that I have destroyed his card and expects me to repair it. Personally I suspect that the card had been shot before and he'd just not noticed it in his measurements (which isn't all too plausible either). Malevolence on his part, weirdness aside, can be excluded.robert

Feb 28, 2007 21 Replies

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Joerg 19 years ago

No schematic? That's usually the time to crack out the near-field probes or make one and hang it onto the scope, to find the offender. Much less risky than walking the pins on a bunch of 0.625mm spacing TSSOPs.

Regards, Joerg http://www.analogconsultants.com

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joseph2k 19 years ago

They ask you to fix it and do not provide schematics? I haven't put up with that since the mid 1970's. Though i bet it is getting harder now days.

JosephKK Gegen dummheit kampfen die Gotter Selbst, vergebens. --Schiller

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