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Op-amp failure

Hello,

I'm having problems with a DAC circuit I've built using ADI's AD5443 chip. The circuit is based on the evaluation board schematic provided in the data sheet. The design is quite straightforward and includes a +10V voltage reference, the AD5443 chip and a current-to-voltage conversion op-amp (I'm using the recommended AD8065) which provides a unipolar analog voltage output from the DAC's current output.

Initially the circuit worked fine and I was able to run several tests. Then there was sudden failure, the source of which, after some probing, proved to be the op-amp. So I replaced it with a new op-amp and tested the circuit again. Again it worked fine on the first run of tests (for the testing I'm simply sending

3 SPI logic signals from an FPGA and reading the output data) and then nothing. I'm now onto my third op-amp and have the exact same problem.

I can't fault the design which I just copied from the data sheet so I haven't a clue what the cause of this is. Any ideas?

Thanks.

Mees

Reply to
m_oylulan
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m snipped-for-privacy@hotmail.com wrote: (snip)

Start us off with a link to the data sheet, so we can see this design.

Reply to
John Popelish

I see the design requires several power supplies. Are you sure the supplies get powered up all at the same time? If the 5V supply came up first it's possible the inputs to the Op Amp get overdriven.

For safety I'd add some current-limiting, like 1K ohm resistors in series with the input leads of the op-amp, and maybe another one at the output (Or whatever value the design can tolerate without excessive offsets and frequency droops). And static-protection diodes at all the off-board connections. Cheap protection at a few cents a diode.

Reply to
Ancient_Hacker

Also, some amps have a pathological trend (snapping into high cross current and sizzling out) when one of their inputs gets pulled too far beyond the allowed common mode range. Not sure about this one but worth checking.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

For a link to the data sheet:

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All the parts are powered from the same source (+/-12V and 5V dual power supply with comm> Also, some amps have a pathological trend (snapping into high cross

I've tested the design with a different op-amp OP-97 instead of AD8065 with similar results.

Mees

Reply to
m_oylulan

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