Setup
- Robust 12V supply, IE, a battery with good charge, on charge @ 13.5 - 14.4V
- Secondary supply of 5 - 15V completely independent so as to be able to apply negative voltages
- Solid ground and power wiring to the battery with say a 20A fuse to prevent fire
- 1 DPAK under short circuit conditions (0.1ohm shunt) to 12V supply directly (or through the 20A fuse) traces should not burn, record hold current
- 1 SOT223, same as above.
- 1 DPAK under negative Voltage conditions, observe any/all behaviour(s).
- 1 SOT223, same as above.
- Use bench test to put each FET under thermal load with 80% duty and 5A load, realistically you can expect all 8 DPAKs to carry as much as 2.5A each worst case, perhaps heat test in parallel and ensure board survives extended length test?
- Each protected analogue input individually connected to 12V supply and then negative supply with Voltage @ MCU and Voltage @ rail measured and verified as OK in each case.
- Progressively connect all protected analogue inputs to 12V supply and measure supply rail after each addition. Also monitor heat in clamp circuit, and if possible, even if through modification, monitor current through clamp circuit too (insert a shunt resistor of 0.1ohm?) until finally having all analogue inputs shorted to 12V without a blown supply or MCU. (hopefully)
- Force a potential of 12+ Volts (use 110V AC mains if you're brave, should be fine, layout/isolation dependent) between the comms ground and circuit ground and ensure comms are reliable (power board with 9V battery or other convenient isolated source) and ensure laptop is unplugged and running independently too.
- Overload 5V output to level necessary to trip fuse and record what that is. I don't recall which fuse you used, but if it's got too high of a trip current, the regulator could bail first, if so, we need to revise the fusing or regulator.
- Short ignition drives to ground with 12V out and 12V with ground out and ensure both IC and resistor do not overheat.
- Scraping bottom of barrel now, but perhaps try to induce instability in each power supply by externally switching a 500mA load at a moderate frequency? Observe stability of both supplies CPU behaviour?
If you can get good quality footage of any of the tests with a commentary that'd be cool too, but not necessary.
Any other ideas welcome too. Huff may have some acid for us.
Fred.