Electronics > Projects, Designs, and Technical Stuff
Lead length to bypass cap "must exceed 20mm" ??
Arjunan M R:
It's a mistake.Look at their evaluation board.The caps are not that far away from the ic.
T3sl4co1l:
--- Quote from: coppercone2 on May 28, 2019, 04:52:14 am ---
--- Quote from: T3sl4co1l on May 28, 2019, 04:03:19 am ---They're CMOS with a somewhat hefty stage driving the monolithic air core transformer. No different from, say, 74LVC logic driving runt pulses.
Tim
--- End quote ---
Are you sure? I thought I saw the waveforms on one of those devices in the datasheet (may have been silicon laboratories) where they show a nice sine wave based on/off modulation, like they are connecting and disconnecting a power amplifier from a oscillator, not digital logic driving magnetics??
figure 20 of the datasheet link shows a sinewave/evelope detector deal
--- End quote ---
1. They're just showing the concept, not the particulars.
2. The drivers may well be slow enough that it looks pretty rounded! RF amps in CMOS are the same basic thing, from 125kHz RFID tag readers to Wifi radios (the latter being rather more careful in design, however).
Tim
capt bullshot:
--- Quote from: T3sl4co1l on May 28, 2019, 06:10:46 am ---
--- Quote from: coppercone2 on May 28, 2019, 04:52:14 am ---
--- Quote from: T3sl4co1l on May 28, 2019, 04:03:19 am ---They're CMOS with a somewhat hefty stage driving the monolithic air core transformer. No different from, say, 74LVC logic driving runt pulses.
Tim
--- End quote ---
Are you sure? I thought I saw the waveforms on one of those devices in the datasheet (may have been silicon laboratories) where they show a nice sine wave based on/off modulation, like they are connecting and disconnecting a power amplifier from a oscillator, not digital logic driving magnetics??
figure 20 of the datasheet link shows a sinewave/evelope detector deal
--- End quote ---
1. They're just showing the concept, not the particulars.
--- End quote ---
Yes, we've experienced some real electromagnetic emission issues with these ADUM parts. Not the gate drivers in particular, but the Delta/Sigma frontends. You'll have to place the decoupling caps as close as possible and you need some GND and VCC planes to cope with them. Their internal CMOS drivers emit quite fast transients through the supply pins, causing trouble at several 100MHz when doing EMI compliance testing. So Tim is right about the internal structures, this was confirmed by ADI also. In more recent parts, they've changed the modulation scheme, maybe this reduces EMI also.
Otherwise, for the 20mm minimum length requirement (this cleary doesn't apply here), I've done such specs before. In this particular case to add some ESR to a ceramic cap to keep the LDO from ringing / oscillation. Beware, you'll also have to specify trace width and thickness too.
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