That, too, but the usual thin film parts can also suffer substantial parameter changes:
formatting link
Can you place the clamps right at the pin and then a resistor to wherever it needs to go? That way a few hundred ohms would suffice and there is no overvoltage on the resistors.
OK caveat first, don't listen to me and do whatever Joerg says. But I stuck diodes(clamps) right on the pins (maybe at the end of wires) and zapped a laser diode with one of those peizo sparkers in butane lighters. (all over the place.. both ways...) I guess I figure the ESD diode's are big enough to take the energy.. (actually, I thought nothing like that at the time.. it worked and I moved on.)
1/2CV**2~(call V = 10kV to make math easy.. and ignore 1/2..-10+8~10mJ Why the 10k ohm resistor? (Hey maybe I should add bit of resistance?.. I could afford a few ohms.)
I also need to be able to stand a +-30 DC overvoltage, so I want to keep the R values up, and I can't clamp the inputs lest people blow up the clamps.
The pins lead, through the resistors, to the diff input of a 24-bit delta-sigma ADC. Ultimately, I'm measuring RTDs.
I guess I could put capacitors to ground at the input pins. 10 nF or so maybe. That would make a divider/lowpass with the 100 pF body model capacitance.
I wonder if a 10K 1206 would mind a 4 KV zot. Probably not. I guess I should try it. I've got an old Kepco 4KV bench supply somewhere around here, with one tube inside.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Carbon resistors may be an option, they can take such hits easier. But ideally it should be thick non-trimmed ones, assuming tolerance is not an issue and you run it in ratiometric fashion.
That is not high-tech, too pedestrian :-)
The rail for that doesn't have to be actively managed. It could be "pumped up" by pulses only when the system gets hit with voltage levels past its normal supplies.
4kV will nominally jump 40mils... add some San Francisco "fog" and who knows. Maybe use a carbon? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
The 10K limits the current into the ADC chip inputs if the customer applies 50 volts. The ADC is rated for 10 mA max input current into its ESD diodes.
If I clamp at the input pins, I'd need +-50 volt clamps so I don't vaporize them with the specified DC overload.
I'm trying to be zen about this, not clamp/fight the overloads, but limit the currents. So, if a 1206 series resistor can't stand the ESD zap, maybe a cap at the input pin is the best way.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Well as long as whatever is driving it can stand the 10nF caps. (and whatever time constant that means.) For protection carbon comps are nice (as others said), but I'm guessing they don't come in surface mount.
(We use through hole carbon comps as termination resistors for an RF coil because they have non-magnetic leads.)
For lightning protection some time back I fielded two schemes for protecting hi-z differential analog mux inputs: - 10K carbon comp. in series with both inputs, 1uF differential cap, diode clamp - diff. gas discharge arrestor, 100k 1/2w series (both leads), 100nF differential cap., rugged CMOS mux
The idea was to limit worst case Vin to something sane, then limit mux current to something safe. (I made an IEEE surge waveform generator to blast it.)
Field failures stopped. (Except for the one, a direct hit. Lightning vaporized a bunch of the heavy steel box, and a big part of the board.)
Your zen solution is distribute the 4kV zap over a series resistor string that can handle it. Or gobble it with a cap, if you can stand the CMRR hit.
In theory, the chip is already designed for human body model. So yeah, a little capacitance will do the trick.
You could probably go a little lower on the resistance if need be. Most chips are designed for 40ma injection, so even 10ma wouldn't be that bad. You need to insure that your power supply won't be pulled up with the external current.
All that is required under injection is the part won't latch up. There is no assurance that the part won't need to be reprogrammed, assuming it has internal registers. Or that the internal logic won't be hosed after injection. If you really want a rugged system, you should detect the external overstress then reset the system. Or use an analog watchdog chip. There is nothing worse than need to boot some measurement system.
On a sunny day (Mon, 28 Apr 2014 15:23:58 -0700) it happened John Larkin wrote in :
Yes why not?
Actually whats wrong with a simple series resister (of high voltage capability), and a neon to limit volts, and then an other resistor?
in --- Rhv ------ R ----- out | 0 about 80V pp 0 neon | /// The advantage is no leakage in normal situation. There are many gas based surge arrestor types..
I nearly suggested tight-spaced pads on the layout--a home-made spark gap--just for fun. But that would be a nasty, carbonizing, metal-spalling dirt-magnet.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.