Oh yeah, test-lead inductance. 3 feet of Pomona test leads for Vcc and GND (6 feet round trip). The board I was debugging is a nixie wristwatch, and it has a small DC-DC converter that takes the 3.7 to 4.2V supply (typically a Li-ion battery) down to 3.25V to run the onboard FPGA and display drivers. Even though it's low current, say 100mA max, the DC-DC converter runs at 2-3Mhz, and has very sharp current spikes. I couldn't figure out why the converter would start, then shut down a few hundred usec later. There was all sorts of ringing on the power supply, and I had assumed it was bad probe-grounding, because I could alter it with ground clip location.
Only after I removed the ground clip, and connected to the metal sheath on the probe did it become clear I had noise on the power supply. When went to battery power (total wire length of about 1 inch), the converter ran perfectly. Using the same short leads with the bench supply (as on the battery), it also worked. From what I could tell, the noise was so bad that the DC-C converter IC became inoperable. 6 feet of testleads is about 2uH. The inductor in the converter is 1.5uH, so the testleads definitely have a major impact on the circuit. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/4170505c-4326-42e1-b332-d1a6b8175f79%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
