Signals ADC_5V and ADC_3V3 back to the host should be a bit high by maybe a tenth of a volt.
If the processor doesn't see a high enough voltage,? it waits until it does before running any further code.
It's ok if those signals are a bit high, but there is no margin on the low side.
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I'm amazed the 78M33 works at all, that's a lot of power to dissipate.
I'd recommend either going with a bigger regulator (and a heat sink), or feeding the 78M33 from your 5v linear..
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Jerry, KE7ER
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On Tue, Jan 7, 2025 at 06:32 PM, Adam wrote:
2. CPU needs two fake signals: ADC_5V (2.5 V) and ADC_3V3 (1.65 V). The
reason is that it still tries to drive nonexistent SMPSes, expecting
feedback on these two lines. It won't boot without them. Just provide
resistive dividers, like in the original design (resistor values are not
critical, I used 18k).
