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I found out that firmware was expecting the start pin to be pulled low instead of high. I’m not sure if this is necessary because the datasheet seems to suggest that data can be read from the ADC in continuous conversion mode, but I still attempted to change it. I couldn’t cut the 5 V trace on the PCB because it continues to the LTC6820. Instead, I decided to try lifting the pin off the PCB, soldering a wire to it, and then soldering the wire to ground. After the wire was soldered to the pin, the pin twisted and snapped off while bending the wire. In hindsight, I should have just put Kapton tape on the pad. Now that the pin was gone, I just soldered the wire to the stub that was left and even though it’s delicate, it seems to work. The firmware smoke test required some changes to make it work. Here’s all the changes I can remember at the moment:
The read register command wasn’t sending the byte that indicated how many registers to read. This was an oversight from firmware and was never programmed.
The ADC’s internal reference bias was not enabled. This is required for the current sense amplifier to output the correct value.
The value of the reference in firmware was wrong. It was corrected to 2.5.
After fixing the above problems, the ADC readings were fairly accurate. Here are the inputs and outputs during testing:
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