We are using a custom carrier board for the Nano and require it to boot when powered every time. We copied the startup circuit from the carrier board reference schematics (leaving out the power ON/OFF buttons), but for some reason the Nano does not boot about 5-10% of the time. We cannot find a repeatable way that it fails either. Here is the logic circuit:
The only thing left out is the diode between POWER_EN_Q and POWER_EN_Q_R. What is the purpose of that diode? And would that cause the latch circuit to fail sometimes?
Upon further investigation, the circuit on our custom board is working as intended. We increased C52 to ensure POWER_EN triggers after 400ms, and found that the startup circuit works as intended 100% of the time (using an o-scope on POWER_EN). We were able to verify that on some occasions (mostly when the module has been off for a few hours), the module fails to start-up, even when the startup circuit triggers POWER_EN every time.
I don’t want to hijack this thread with other potential solutions, but if there are any recommendations on where to investigate that could cause the Nano to fail to boot occasionally on a custom board, I can create a new topic.
