The firmware needs to see the voltage at the 3.3V ADC line exceed 1.65V and that at the 5V ADC line exceed 2.5V. So it SHOULD work if you provided externally produced 3.3V and 5V rails, as long as the ADC inputs were sufficient for it to get past the SMPS initialization. Connecting both ADC inputs to?+3.3V Vdd would work.?
As for power dissipation if the 3.3V regulator is permanently used... I don't think there would be any problem with the 78M33 being able to cope with it. But I have not tested this scenario at say 12V supply.?
On Thu, Aug 17, 2023 at 7:26?PM Bojan Naglic <bojan.naglic@...> wrote:
Hi, a question to Hans: What if the PCB #2 SMPS card is not present (or is faulty)? So the ADC 3V3 signal line would be open. Does the FW algorithm let the 3V3 linear regulator work for VDD instead? And does the LDO in this case withstand the constant dissipation?
In other words, if one decides to operate the 3V3 rail from a linear regulator or to just troubleshoot using this option (without the PCB #2), would it be enough to ground the ADC 3V3 line on the connector?
