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| OSHW - 24bit ADC measurement system for voltage references |
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| branadic:
Found an intersting link today and I can't remember that it was linked somewhere on eevblog before: Long term characterization of voltage references |
| rs20:
Just a thought, and feel free to point me to another thread if this has already been discussed, but the cut-outs around the voltage reference seem a bit sub-optimal? There are little PCB bridges on all four sides of the voltage reference "island", which means that that island can't freely thermally expand or contract. I don't see that thermal stresses will be reduced much at all. The suggestions in the relevant datasheet, to have a cut-out running continuously around all three sides of the reference so that it's freely cantilevered in space seem more effective and more space-efficient. |
| branadic:
Please refer to the video available by Linear Technology (Brendan Whelan) that suggest this 4-sided cutout geometry to give similar or better performance compared to the 3-sided pcb tab cutout: http://www.engineeringtv.com/video/Linear-Technology-LS8-Package-I (watch minute 6:34) Furthermore you have the advantage of running the traces over the corners instead of having all traces at one side. So, I preferd using the 4-sided cutouts and while the device runs within +10°C ... +40°C I'm not affraid of any form of cutouts. |
| rs20:
Point taken, although I can't reconcile this with my intuition. Interesting that the context was FR4 swelling due to humidity. I'd be curious if anyone's come across some actual studies on this -- all the video tautologically says is "A can give similar or better performance than B", which doesn't rule out A being better than B at all. </ot> |
| Andreas:
--- Quote from: rs20 on July 06, 2014, 07:08:30 am ---Point taken, although I can't reconcile this with my intuition. Interesting that the context was FR4 swelling due to humidity. I'd be curious if anyone's come across some actual studies on this -- all the video tautologically says is "A can give similar or better performance than B", which doesn't rule out A being better than B at all. </ot> --- End quote --- You are invited to do some studies on this. I for my part prefer the "dead bug in hole mounting" method for LS8-devices. (do not try this in production). https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg278825/?topicseen#msg278825 A other method would be mounting the reference on a ceramic substrate with the same CTE than the housing of the reference. Or using a flexible part of a PCB (kapton foil) for the mounting of the reference. With best regards Andreas |
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