We got a few moments of "free time" and followed up with the second 3303X-E calibration. As mentioned this second 3303X-E was required to support and on-going design effort, it was "enhanced" to a 3303X following the procedures outlined here, same as was our first 3303X-E awhile back.
The 1st 3303X is used to supply critical voltages to expensive chips and has the current limits set to under 20ma, just above the normal operating currents. This has already saved the day
A certain dumb arse we won't mention
used a standard Raspberry Pi breakout PCB for the 40 pin GPIO connector to get access to the 40 analog DAC channels which are on a 40 pin header and are used to drive HV amplifiers, Bi-Phase modulators and Bi-Polar offset modes in another custom PCB. When the system was turned on and commands sent via SPI to activate the various individual channels, certain channels would cause an overcurrent condition and the 3303X would go into a limit condition. This was thought to be due to shorts on the 100 pin LQFP device, after carefully viewing and probing under a microscope this was not the case, which then led to examining all the custom PCB traces for possible shorts without any discovered. So back to the setup but without the IO connector in place, no overcurrent, but with the IO connector and overcurrent condition
Turns out the breakout PCB doesn't route each individual pins to the male connector as expected, but ties the various common pins of the Raspberry Pi GPIO together, thus shorting certain pins as experienced
Anyway, the second 3303X was used for a more general supply of for VCC and VEE use and current limits set to an arbitrary 100ma and not verified. After calibration it was noted the current limit was engaged at ~80ma on both channels without any load!! This was thought to be a calibration issue and all the memory was reset and another calibration performed, the result was the same. After many memory and power resets, multiple calibration attempts, this condition still resides even tho the current readings are very accurate over the entire range, as are the voltage readings. This high OC condition seems to be an offset since the readings at actual currents also show an offset of similar value (~80ma). Both supplies exhibit very accurate voltage and current readings over the supplies full range, however only one has the correct current limit settings which are quite accurate, even at the lower ranges which was impressive performance IMO.
Both have the same firmware (1.01.01.02.05), same hardware (V3.0), same product type SPD3303X, so beginning to think this second unit has a hardware issue with the current limit circuit.
BTW I had no idea just how good this supply is regarding voltage, current and current limit accuracy (one at least), until we needed a precision voltage with low current limit and it save our butt
Would appreciate if a few others with these "enhanced" 3303X-E could check the current limits at lower levels like 40ma, 20ma and 10ma and report results.
Thanks in advance for any help.
Sorry for the long thread, but figured others might appreciate how this all transpired, and why a precision supply is very valuable for lab use.
Best,
Edit: Here's the setup for the project with only 4 channels, will grow to at least 64 and likely 100. Of course the multiple instances of these PCBs will be integrated into a custom PCB base, and all the Power Supplies (+-75V, +-7V, +5V, +5.5V, +6V) will be replaced with a custom PS running from a single 12V input also supporting custom computer interfaces with USB, SPI and RPi interfaces.