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turns out for the 1.1A limit i forgot that i set the power supply limit to 1A LOL so yeah of course when I increased that, the output was enabled for higher currents
back to the enabling input problem, I notice that the valid1 pin is always low and the other valid pins are always high no matter the configuration of the input supplies → a low valid pin means the presence of a supply should be detected and allowed to turn on output in the case of priority
turns out there is a short to ground on the VALID1 pin, so im gonna check all the solder
after probing around the board and fixing a few solder joints, it seemed that the entire current sense resistor for DCDC input was not soldered down. One thing to note for next rev is that the pads for the resistor should be bigger so its easier to solder down, as the resistor pads almost perfectly fit the footprint pads.
finally the input from dcdc is going to the LTC4417, however the output is still not being enabled (there is only input on the dcdc connector)
I noticed in this case the VALID2 pin is low and the rest are high, meaning that DCDC is enabled, however there is still no ouput.
I then noticed when i connect DCDC and aux, the output is still 0, but when i connect only aux, the output is non zero, which means that the ltc is prioritizing correct and therefore the issue is turning on the fet. I noticed that with Aux input, TP1= 10.6V, TP2=0.4V, TP3=7.29V and with DCDC connected, TP1= 8.2V, TP2=0.0V, TP3=0V. will match them to their gates to see what is wrong next time.
Next day of troubleshooting and im resoldering all the fets to see if thats the problem, because aside from the power supply mux fets seemingly turning on for only aux input, there doesnt seem to be an LTC problem from the above numbers. I am finding that soldering down the fets is incredibly difficult because of how large the associated poly pours and copper is. For next rev, we might want to minimize the poly pours by recording how much they heat up from this testing and adjusting accordingly.
YES it finally works 😃 turns out it was a fet soldering problem, look at the above^
i tested priority between dcdc and aux, and dcdc always takes priority which is good. Something else that josh wanted to test was the switchover time from output turning on to input being supplied. I used the scope to plot both input and output and compare timing. See below for a difference of about 300ms
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