ESD protections
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From: linnix on 18 Apr 2010 13:17 We are making a device with 18 inputs and 12 outputs, plus USB signals. We are concerned about EMI/ESD protections. There is ferric core (for EMI) and clamping diode (for ESD) on the USB line. Should we also protect the I/Os against ESD? Are inputs more critical than outputs? We can also change the buffer/decoder chip. Is older fab tech (0.5 vs. 0.35 micron) better for ESD, with bigger components? Thanks.
From: Jamie on 19 Apr 2010 01:57 linnix wrote: > We are making a device with 18 inputs and 12 outputs, plus USB > signals. We are concerned about EMI/ESD protections. There is ferric > core (for EMI) and clamping diode (for ESD) on the USB line. Should > we also protect the I/Os against ESD? Are inputs more critical than > outputs? We can also change the buffer/decoder chip. Is older fab > tech (0.5 vs. 0.35 micron) better for ESD, with bigger components? > Thanks. yes, unless you have optical protection on the inputs, it's very important to protect the inputs with TVS type diodes.. And you may want to use the unipolar type, if the input is sensitive to reverse polarity.
From: D Yuniskis on 18 Apr 2010 14:36 linnix wrote: > We are making a device with 18 inputs and 12 outputs, plus USB > signals. We are concerned about EMI/ESD protections. There is ferric > core (for EMI) and clamping diode (for ESD) on the USB line. Should > we also protect the I/Os against ESD? Are inputs more critical than Think about where your I/O's are going. E.g., chances are, the USB port is "exposed" to the user "casually". If, OTOH, the other I/O's are tied to the field in such a way that they aren't *intended* to see "service", you can dramatically change the signal conditioning that you deploy to better suit the service they *will* see. > outputs? We can also change the buffer/decoder chip. Is older fab > tech (0.5 vs. 0.35 micron) better for ESD, with bigger components? > Thanks.
From: linnix on 18 Apr 2010 14:50 On Apr 18, 11:36 am, D Yuniskis <not.going.to...(a)seen.com> wrote: > linnix wrote: > > We are making a device with 18 inputs and 12 outputs, plus USB > > signals. We are concerned about EMI/ESD protections. There is ferric > > core (for EMI) and clamping diode (for ESD) on the USB line. Should > > we also protect the I/Os against ESD? Are inputs more critical than > > Think about where your I/O's are going. The I/Os are routed to a connector, then a flexible cable of 30cm. But it could be subject to ESD while connect/disconnect the cable during installation. ESD protection will double the cost (mainly 4 layers vs. 2 layers PCB) for added components. Short term (5 to 10% returns due to damages) is manageable, but long term might not. > E.g., chances are, the USB port is "exposed" to the user "casually". USB is fully protected, since there are only two wires. > If, OTOH, the other > I/O's are tied to the field in such a way that they aren't > *intended* to see "service", you can dramatically change the > signal conditioning that you deploy to better suit the service > they *will* see. > > > outputs? We can also change the buffer/decoder chip. Is older fab > > tech (0.5 vs. 0.35 micron) better for ESD, with bigger components? > > Thanks.
From: larwe on 18 Apr 2010 16:57 On Apr 18, 3:57 pm, Archimedes' Lever <OneBigLe...(a)InfiniteSeries.Org> wrote: > >> Optoisolation is better still if you can manage it. > > >Too expensive. > > Bullshit. Maybe not. Look, there is a spectrum of protection vs cost, I can accept that. In fact in my day job we do not use optoisolation for this reason exactly. But when I've done a contract vending machine project, I used optos on every input because my experience with coin- op arcade games was that they frequently die when people use piezo zappers on them...
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