Jerry, I am glad you use very appropriate ESD precautions for your kit assembly.?

I would venture to guess that most QMX kit assemblers are not as careful, and may not even be using an anti-static mat (based on photos they have posted).

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Regarding the PCM1804, On Thu, Dec 5, 2024 at 07:51 AM, Jerry Gaffke wrote:

From page 2 of the TI datasheet we see this fairly standard disclaimer:? "These circuits have been qualified to protect this device against electrostatic discharges (ESD) of up to 2 kV according to MIL-STD-883C, Method 3015; however, it is advised that precautions be taken to avoid application of any voltage higher than maximum-rated voltages to these high-impedance circuits."?

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Yes, the PCM1804 and the STM32 processor have ESD protection built in.? But PLEASE do not confuse this with the need to take proper ESD precautions during assembly.? The built-in protections on these devices will protect the devices during reasonably careful handling, but will not protect against common ESD events if you don't take ESD precautions.? Note the following table taken from an ESD training course ()

Just moving around at your workstation, or picking up a plastic bag of parts will generate many thousands of volts of static charge, many times the level of protection built into the devices.? And you don't even have to directly touch the device for damage to take place - just getting your charged finger close can allow the static discharge to occur.? And you don't have to see a spark - damaging ESD takes place at much lower levels than those that cause a visible spark.

If static was such a prevalent issue during the build of these kits, I'd expect blown BS170 gates to be more prevalent than blown PCM1804's.

This is a mis-conception.? Yes, the BS170s are also sensitive to static, but their gates are over 1000 times larger than the gates of the many tiny transistors in the PCM1804.? An ESD event that would cause a very minor defect in the gate of a BS170 could blow out or damage several transistors in the PCM1804.? It is very interesting to view electron-microscope scans of ESD events - they blow little 'craters' in one or more layers of the semiconductor material, sometimes just leaving a tiny hole in a non-important place, other times destroying transistor gates, or partially blasting through metal layer traces, which later fail like a fuse, etc.

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So yes, since I understand that the PCM1804 functionality is tested at the factory before shipment, I re-assert my belief that many of the reported PCM1804 failures are likely happening due to ESD issues during assembly (including the failure that I had), and likely have nothing to do with the small over-voltages that can make it through the smps L-C filter and protection diode.

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Stan KC7XE