This page will outline my validation and results and troubleshooting for the power select board.
The first test is kinda a smoke test → I will have 5V initially on the Aux input from a power supply, and the eload connected to the output in CC mode currently drawing 500mA (to start off) → I will then increase the input voltage to see when the output is connected
I may have figured out a logical flaw → for the LTC4417 to be enabled, there must be a 3V3 output from the controller board. However a standalone controller board needs 12V input to have the 3V3 reference, except that 12V in the schematics seems to come from the output of power select, which only has a 12V reference when the LTC is enabled. Therefore, it should never enable standalone
I connected the controllerboard to my laptop for the 3V3 reference, and started the power supply at 5v, with the eload showing that it has around 70mV. I increased it in 1V increments until it reached 10V output, in which the eload suddenly changed to 9.998Voc, meaning the LTC was regulating the supply! Note that at this point, I took out programmer from my laptop, and I still see the 3V3 rail which further verifies my assumption is probably right. see the following table for some points
Voltage input (Aux) (V) | Current on Eload (A) | Voltage on output (V) | other notes |
|---|---|---|---|
9.7V | 0.5 | 9.63 | The turn on voltage, before this point (100mV increments) there is no output |
10.01 | 0.5 | 9.94 | before this point (1V increments) no output, and I had to connect the programmer again to enable the LTC4417 again |
11.01 | 0.5 | 10.89 | During this step, I increased the current until it turned off which was 1.1A (1A was fine) |
12.01 | 1 | 11.83 | I increased the current again to 1.1A, and the LTC turned off |
13.01 | 1 | 12.83 | |
13.98 | 1 | 13.81 | |
15.98 | 0 | 0 | I increased this in 1V increment to this point where the LTC4417 turned off again |
important note from the above table, no matter the valid input reference level, the output would only be enabled if the eload was set at less than 1.1A. not sure why → will ask josh
before i left for the day, I tried to see if the priority system would work → for some reason the supply on the DCDC input did not ever seem to allow output no matter the condition. I switched the supply as well and it still wouldnt allow output.
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.