I'm working on a design that has digital isolators and a 14-bit a/d on the same board. The app notes say Analog Devices' isoPower isolators pound 700mA 1nS spikes into their power supply pins at up to 300MHz.
Nasty.
Anyone tried this?
-- Cheers, James Arthur
We use the ADUM1400 and 1401 data isolators, 16 to a board, on a couple of products, and 12 on the new one I recently posted a pic of. The two 16-channel ones are microvolt-resolution things, one input and one output.
The input module uses a 24-bit delta-sigma ADC, and the output thing uses a 16-bit dac per channel. We haven't seen any problems from RF feedthru affecting our analog stuff, but we haven't tried to pass FCC or CE with these. We do the power coupling with ISDN-type transformers at around 80 KHz, with soft-edge drive.
If you're concerned about the power one getting into a fast ADC, I'd suggest some common-mode inductors on the input and/or output, and some caps to ground wherever you can stand them.
Incidentally, SiLabs has compatible data couplers for about half the price. We're qualifying them now.
John
Thanks for the info.
AD's dire warnings seem to be for their isoPower units (the ones that also generate isolated power). The straight isolators don't seem to be nearly the problem, noise-wise -- the dc-to-dc part is the jack- hammer.
This board's pre-existing, the A/D's slow, but SAR, so you wonder why that's not been a problem.
I'll isolate the Vdd's with beads to start. That should be a monster step up from what's there now.
James
snipped
Meaty, beady, big and hopefully not too bouncy. :-)
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