how to safely observe VCC behaviour of a DUT with a DSO during an ESD event? - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: August 11, 2014, 07:34:59 pm
content: Ineedtoseewhat's happening to my device during an ESD event (I'm simulating it by using an electronic BBQ igniter).Even if I don't have a DSO with the needed bandwidth to capture the discharge in detail (or even see it!), I should however see any glitches or spikes to the various parts of the circuit (VCC, GND, I/Os etc.) and see how (and if) effective are the solutions I'm trying to implement to avoid any ESD issues.I don't have any high voltage probe to use.A 1MOhm resistor, rated for high voltages, in series with the DSO probe set at 10x, may be enough?

author: AndyC_772
author_rank: Super Contributor
timestamp: August 11, 2014, 07:46:24 pm
content: I doubt you'll see anything useful. ESD events transmit wide band radio interference, which will be picked up by your probe cable and will appear on the scope trace whatever you do.What, specifically, are you looking for?

author: mcinque
author_rank: Unknown
timestamp: August 11, 2014, 07:57:53 pm
content: Thank you for your reply.I'm looking for voltage spikes on power rails and/or spikes on digital I/O.I want to understand if the ESD event does not discharge fully to the ground or if the issue is (like you said) a matter of radio interference.

author: David Hess
author_rank: Super Contributor
timestamp: August 11, 2014, 08:18:59 pm
content: I have not had the problems AndyC_772 describes when using a coaxial probe environment and ground loops are avoided. The usual rules for high frequency probing apply regarding long ground clips. Ground loops can be detected by running the test with the probe shorted at the measurement point. High voltage differential probes might deliver better results and the same shorted probes test applies. In some cases the test point can be connected directly to the oscilloscope which I might try with heavy double shielded coaxial cable.Usually there is some interference no matter what you do as Dave has shown in some of his videos but with care it is manageable.It probably will not hurt it but I would not bother trying to measure the ESD directly with the oscilloscope. The energy levels involved are just not that high. What is normally seen is abnormal circuit operation. Relative measurements are useful to evaluate various mitigation measures.

author: Andreas
author_rank: Super Contributor
timestamp: August 11, 2014, 08:47:49 pm
content: Quote from: mcinque on August 11, 2014, 07:34:59 pmSorry but I doubt that the BBQ igniter produces similar results that can be compared with ESD.(risetime, pulse width, peak current, energy).So the results (and your measures found by the method) will help against BBQ spikes but not necessarily against real ESD.On the other side by setting your probe you will change your D.U.T. (device under test).The ESD currents without probe will flow a different way as with probe. (and different parts may be influenced).Especially when using a plastic housing or a not fully shielded device.(So probably you have to sell your devices with the oscilloscope attached.)With best regardsAndreas

author: mcinque
author_rank: Unknown
timestamp: August 11, 2014, 09:17:13 pm
content: QuoteYou're right.Quote